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How to Learn Physics for Free - 2026 Edition - The Quantum Cat

2026-02-03T14:03:09.000Z

I made the first version of this guide back in 2023 with the intention of collecting a set of free resources sufficient to guide a reader through the field of physics. Since then it has become my most popular post with tens of thousands of views. Over time things get out of date, links break, and new resources become available - this update is an effort to tidy things up a bit, fix anything that has broken, and to add a few new links I have found since 2023.

On this page I have gathered a list of free resources for learning physics. My intention is to cover the main areas of modern physics for the interested reader, stretching from Newton’s laws to quantum field theory and beyond.

To really learn physics you should, of course, enrol in a university degree. But for those who are simply curious or who lack the time for full time studies, I hope this guide will be of benefit. For those who do decide to study physics more seriously, it may also act as a companion; a set of resources to aid you in your study.

How to Use This Guide

Please don’t let the perceived difficulty of physics and maths put you off. Like anything else, these are subjects that can be learned, and can be done so by pretty much anybody. It may take time, it may be frustrating at times, it may occasionally go slower than you would like. But it can be done.

Below I have divided modern physics into its more or less accepted subdivisions. The biggest of these, of course, is the split between the “classical” physics of Newton, and the modern physics of Einstein and Quantum Theory. Within each are further sections: mechanics, thermodynamics and electromagnetism for classical physics, and quantum theory and relativity for modern physics.

For each I’ve provided links to free online textbooks and other resources. Where possible I have linked to material prepared by well-respected physicists, and I have tried to offer a range of options for each subject. If one book is not working out for you, then feel free to abandon it and try a different one from another author.

The links also differ in difficulty and scope. Those marked in bold should be considered as “essential” material, that alone is sufficient to give you a general understanding of physics. The rest is optional, but studying it will give you deeper insights into the topic.

You should work through the material in roughly the order presented. Later textbooks will often assume knowledge taught before, and trying to leap into them too early will be more challenging than necessary. To get the best results you should also attempt to complete the problem sets included in many of the textbooks.

This list is (and always will be) incomplete. I have preferred online resources to off-line texts (though some “essential” texts are listed under General Resources). Over time I hope to expand it. Should you know of resources not listed here or find anything that does not work, please feel free to contact me. I will be grateful for your help.

General Resources

To begin, here are several good resources that provide a broad overview of physics. Many of these are also suitable for the more casual reader who is less ready or less interested in going deeper into sub-fields.

Similar Lists

How to Become a Good Theoretical Physicist: A list of resources compiled by Gerard ‘t Hooft, winner of the 1999 Nobel Prize. Broad, with a focus on theoretical physics. Unfortunately it is not yet complete and several links no longer work.

So You Want to Learn Physics…: A guide to learning physics from journalist and former physicist Susan Rigetti. A decent guide, but one more focused on purchasing physical textbooks than taking advantage of online resources.

How to Learn Math and Physics: Another list of resources, this time from Joan Baez, a mathematical physicist at the University of California. Again, heavily based on textbooks, although links are provided where these are freely available online. As you might expect, Baez provides many resources on learning maths as well as physics.

The Feynman Lectures

The Feynman Lectures: Collected in three volumes, Feynman’s lectures on physics make for an excellent starting point and later reference. Feynman, who was famously called “The Great Explainer”, covers his topics in an intuitive and easy-to-read manner.

Textbooks

As opposed to most other resources in this list, the three textbooks mentioned here are not freely available online. I have provided links to Amazon for each - note that these are affiliate links, and you can of course find these textbooks from other bookshops.

University Physics with Modern Physics: By Young and Freedman, this is the standard undergraduate textbook for many courses in physics. Because of that you can often pick up a second hand copy.
Mathematical Methods for Physics and Engineering: Again, a standard undergraduate textbook for university physics courses. This one focuses on the mathematics you’ll meet along the way.
Course of Theoretical Physics: A legendary ten volume series by two Soviet physicists, Lev Landau and Evgeny Lifshitz. More advanced than University Physics, these textbooks are better suited for those readers looking for a deeper understanding and who already have completed the basics.

Pre-Newtonian Physics

Pre-Newtonian physics (i.e., that of Ancient Greece, India and the Arab world) is rarely taught in universities today. Many of the ideas from this time are out of date, incomplete or just plain wrong. I include it here for those who are interested in understanding the path towards a more modern form of physics.

Galileo and Einstein: Despite the title, this course traces our understanding of space, time and forces from Ancient Babylonia and Greece to the modern day, giving a nice overview of how our view of the physical world has changed over the centuries.

Mathematics

Mathematics lies at the heart of physics, and thus forms an essential prerequisite to going further. Here I have gathered material covering much of the maths key to later study. However, the field of mathematics related to physics is vast in its own right. Should you wish for more, see the further resources section below.

Fundamentals of Mathematics

The fundamentals are essential to all later subject areas. Make sure you are familiar with basic algebra, geometry, trigonometry as well as imaginary and complex numbers.

Beginning Algebra: Tutorials on basic algebra provided by West Texas A&M University, covering the essentials from fractions to simple geometry.
Intermediate Algebra: Continue the tutorials from West Texas A&M by moving onto linear equations, more complex fractions and roots.
Dave’s Short Trig Course: Get a deeper look at trigonometry with this short course by David Joyce at Clark University.
Dave’s Short Course on Complex Numbers: David Joyce continues with this quick introduction to imaginary and complex numbers.
Linear Algebra: A free online textbook by Jim Hefferon, covering linear algebra as needed for a standard undergraduate course in physics.

Calculus

Calculus is the mathematics of continuously changing variables. It is what allows us to deal mathematically with velocities (changes in position), accelerations (changes in velocity) and other changing quantities. Historically it was developed by Leibniz and Newton, and is vital to understanding the problems addressed by Newtonian physics.

Calculus Made Easy: An old textbook, but a good one that will give you a friendly introduction to calculus.
Calculus: From MIT, this free book will take you from basics of calculus through to partial derivatives and vector calculus. Working through it should give you the tools to go further into Newtonian physics.
Notes on Differential Equations: After you grasp the essentials of calculus, this compilation of course notes will take you deeper into differential equations and their physical applications.
Multivariable Calculus: This course gives an introduction to multivariable calculus from vectors to Gauss’ theorem. Much of this will have been covered by other resources already, but it is a useful summary of the topic and will find applications from mechanics to electromagnetism.
Advanced Calculus: For a deeper view of calculus and its applications, this textbook provides an extensive overview of the subject.
Primer on Partial Differential Equations for Physicists: An introduction to mathematical techniques for physics. You should already be familiar with partial differential equations before starting this textbook.
Mathematical Tools for Physics: After going through the above, this free online textbook will give you a good grounding in the general mathematics needed for physics.

Statistics

Lies, damn lies and statistics. People are famously bad at understanding statistics; studying it will help you critically evaluate many studies and experiments. It is also crucial to many fields of physics, and especially so for thermodynamics.

Concepts & Applications of Inferential Statistics: Don’t be afraid of the title: this resource is a friendly introduction to the statistical tools needed to do physics, especially of the experimental kind.
Introduction to Probability: From Grinstead and Snell, this textbook takes you through the ideas and techniques of probability. To get the most of this book, you should already have some understanding of calculus, multiple integrals and matrices.

Further Resources On Mathematics

Mathematics is an entire subject by itself, and extends far, far beyond what I have covered here. Rather than devote this page to maths, I suggest checking out the following resources for pointers on how to proceed.

Mathematics for Theoretical Physics: An extensive online textbook covering the mathematics useful for pursuing and understanding theoretical physics. I recommend you to take a look, even if you just treat it as a reference.
Basic Concepts of Mathematics: Despite the title, this book actually provides an introduction to a more rigorous study of mathematics than so far presented. Useful for going deeper into theory.
How to Learn Math: Again from Baez, this list of resources provides a comprehensive path into the field of mathematics.
Online Maths Books: Georgia Institute of Technology professor George Cain has collected this list of freely available online maths books. Unfortunately many of the links are out of date and no longer work.

Classical Physics

Classical physics was developed between the work of Newton in the 17th Century and that of Einstein in the 20th. Though today it has been superseded by quantum theory and relativity, classical physics is still relevant in describing much of the world that occurs at our scale - when, in other words, things are not too small and not too fast.

Mechanics

Classical mechanics begins with Newton’s famous laws of motion and deals with the movements of matter through space. It is a world of forces and accelerations; momentums and energies. Einstein’s theories have superseded it, though mechanics still remains relevant and mostly accurate when working with our everyday world.

MIT OpenCourseware - Classical Mechanics: An online textbook and course provided through MIT OpenCourseware. It provides a solid introduction to classical mechanics.

Newtonian Dynamics: This textbook covers classical mechanics from Newton’s Laws onwards, placing a particular focus on using them to describe the motions of planets and other objects in the Solar System. Worth going through to go a bit deeper into the main areas of classical mechanics.
Classical Dynamics: From Cambridge University, David Tong provides these lecture notes on classical mechanics at an intermediate to advanced level.

Graduate Classical Mechanics: A short online course covering advanced classical mechanics at a graduate level, written by Michael Fowler. A good mathematical background is essential here.
Theoretical Mechanics: Another graduate level course on classical mechanics, this time from the Perimeter Institute.

Thermodynamics

The study of how heat moves. Its development helped us build and improve the steam engine; its consequences, spelt out in the fundamental laws of thermodynamics, predict the ultimate fate of life, the universe and everything. If you think you have built a perpetual motion machine, check here first.

“The law that entropy always increases holds, I think, the supreme position among the laws of Nature. If someone points out to you that your pet theory of the universe is in disagreement with Maxwell's equations - then so much the worse for Maxwell's equations. If it is found to be contradicted by observation - well, these experimentalists do bungle things sometimes. But if your theory is found to be against the Second Law of Thermodynamics I can give you no hope; there is nothing for it to collapse in deepest humiliation.”

~ Arthur Eddington

Thermal and Statistical Physics: By Harvey Gould and Jan Tabochnik, these book chapters, notes and problems cover the main concepts of thermodynamics.
Thermodynamics and Statistical Mechanics: This course by Richard Fitzpatrick introduces the ideas behind thermodynamics and statistical mechanics. Recommended reading to get a good overview of the subject.
Thermodynamics - Fundamentals and Application in Science: This online textbook introduces thermodynamics and then looks at its application to other areas of science, including biology and chemistry.
Statistical Physics: An advanced level course on statistical physics from the Perimeter Institute.
What is Entropy?: A short online book (by Joan Baez) explaining the concept of entropy for non experts.

Electromagnetism and Optics

The mathematical description of electromagnetism was one of the crowning achievements of 19th Century physics. Maxwell’s Equations, first written down in 1861, showed how electricity and magnetism were intimately related; thus opening the door to mastery over those two forces. This, in turn, gave rise to some of the most transformative technologies of the 20th Century: electrical power, radio, television and radar.

Optics: The field of optics was developed far earlier than other areas of electromagnetism and thus can be studied without much of the mathematics needed for the rest of the subject. These lecture notes offer a nice introduction to the topic.

Electromagnetism and Optics: Richard Fitzpatrick provides an introductory course into both electromagnetism and optics, covering the essential basics of the field.
Classical Electromagnetism: Fitzpatrick goes deeper into electromagnetism in this course, beginning with Maxwell’s equations and ending with relativistic electromagnetism.
Electromagnetism: A Cambridge University course on electromagnetism by David Tong. More intermediate level than beginner but worth following.
MIT Electromagnetism: Lecture notes from an MIT course on electromagnetism. You should already have familiarity with Maxwell’s Equations before tackling this course.
Electromagnetic Field Theory: An advanced textbook going deeper into the properties of electromagnetic fields and radiation phenomena.

The Rest of Classical Physics

Mechanics, thermodynamics and electromagnetism are the three primary branches of classical physics. Beyond that, however, classical physics includes many subfields that are either too specific or too advanced to cover above. Below I have collected some resources that fall into these categories:

Solid State Physics: Solid state physics is the physics of materials, and particularly how electrons move through solids and how atoms arrange themselves into crystals and lattices.
Lecture Notes in Fluid Mechanics: Fluid mechanics deals with the motion of liquids and gases, as opposed to solid objects. Technically a subfield of mechanics, but often taught as a separate course. These notes assume a knowledge of Newtonian mechanics.
Fluid Mechanics: A second introductory course on fluid mechanics, this one from the University of Cambridge.
Plasma Physics: Fitzpatrick provides an introduction to plasma physics and then to magnetohydrodynamics, the study of magnetic fluids. An essential topic to study if you are interested in nuclear fusion or the intricacies of stars though, truth be told, this subject is simply fascinating in its own right.
Applications of Classical Physics: A textbook written by Nobel Prize winner Kip Thorne and astrophysicist Roger Blandford. This book covers much of classical physics, with the exception of mechanics, electromagnetism and basic thermodynamics. Both Thorne and Blandford are known for their work on black holes, so it should come as no surprise that the final chapters take the reader into the realm of general relativity.
Richard Fitzpatrick’s Courses: I have linked to several of Fitzpatrick’s courses here. The rest, which do not easily fit into other sections, can be found here.

Relativity

Einstein’s revolutionary theories of relativity reshaped our view of the universe, forever changing the way we thought about time and space. His theory of special relativity arose from efforts to close contradictions in the laws of electromagnetism. General relativity, which came later, radically changed our conceptions of space and time.

Special Relativity

Einstein’s theory of special relativity tackles the motion of light throughout the cosmos. It was born out of an effort to resolve problems with Maxwell’s theory of electromagnetism, and ended with the abandonment of old ideas about time and space. Special relativity, discovered first, addresses the “special” case in which gravity can be ignored.

Notes on Special Relativity: Michael Fowler introduces the ideas of special relativity in these lecture notes, starting from the experiments and theories that motivated its discovery.
Special Relativity: Benjamin Crowell covers the theory of special relativity in this online textbook.
Relativity: The Special and General Theory: Written by Einstein, this book introduces the theories of relativity from the master himself.

General Relativity

The theory of general relativity is one of the most elegant and beautiful ever written down. It speaks of a cosmos in which space and time are intimately linked; in which the presence of matter warps the fabric of both; and from which arises the phenomenon we perceive as gravity. Einstein’s work predicted many strange things, from black holes to wormholes, and reshaped our view of the universe.

Lecture Notes on General Relativity: Sean M. Carroll provides this introductory course on general relativity. It makes for a decent starting point.
Introduction to General Relativity: From Nobel Prize winner Gerald ‘t Hooft, these lecture notes provide a readable introduction to the topic of general relativity.
General Relativity: An Introduction for Undergraduates: If neither of the other introductory courses worked for you, this brief introduction to general relativity may help.
Cambridge General Relativity: Another course on general relativity, this time from David Tong.
General Relativity: By Benjamin Crowell, this textbook covers the theory and geometry of general relativity. Problem sets with solutions are included.
Light Rays, Singularities, and All That: From Edward Witten, this book takes a more advanced look at the implications of general relativity.

Quantum Theory

The quantum world is famously bizarre. Particles can vanish and reappear without warning, cross seemingly impenetrable barriers and somehow exist in two states at once. Even physicists are not immune to this strangeness - few, indeed, would claim to really understand what is happening in the quantum realm. Yet the mathematics works, and the theory provides, so far at least, our deepest understanding of nature.

Quantum Mechanics

Quantum mechanics provides the tools to describe the quantum world. These tools are heavy on mathematics and limited on conceptual understanding, but delving into them will give you a grasp of how things work in the quantum realm.

The Physics of Quantum Mechanics: By James Binney and David Skinner, this book was born out of the second year undergraduate course on quantum mechanics at Oxford University.
Quantum Mechanics: An alternative introduction to the subject, this time from Richard Fitzpatrick.
Cambridge Quantum Mechanics: A first course on quantum mechanics, from David Tong at Cambridge University.
Advanced Quantum Mechanics: A more advanced level course from Freeman Dyson. An old course, but still relevant.

Classical and Quantum Mechanics via Lie Algebras: This book offers an alternative approach to both classical and quantum mechanics from an algebraic perspective. Certainly not useful as an introduction, though it may be of interest to those who wish to get a different mathematical view of quantum mechanics.

Quantum Theory, Groups and Representations: Again going far beyond the essentials, this book approaches quantum theory from a mathematical perspective. Useful if you wish to gain a deeper understanding of the maths and symmetries behind quantum physics.
Introduction to the Theory of Open Quantum Systems: A graduate level course on open quantum systems. Make sure you are comfortable with the basics of quantum mechanics before attempting this - though it is far from essential reading.

Particle Physics and the Standard Model

Our world is made from atoms; atoms are made of electrons, protons and neutrons; protons and neutrons are made from quarks. The standard model describes the subatomic world as we know it today, covering everything from quarks and electrons to neutrinos and the Higgs Boson, as well as the forces between them.

Particle Physics: Based on lectures given at CERN summer schools, this course on particle physics is designed to be accessible to students with high school mathematics.
Elementary Particle Physics: Lecture notes from the University of Rome introducing the subject of particle physics. A good starting point for the subject.
Introduction to High Energy Physics: A second introduction to particle physics, though one that is slightly harder to follow than the course from Rome.
Nuclear & Particle Physics: Another introduction to subatomic physics, beginning with the discovery of the electron, working through to the standard model and ending with an introduction to quantum field theory.
The Standard Model: A Primer: A more advanced textbook introducing quantum field theory through the standard model of particle physics.

Quantum Field Theory

The quantum field theory emerged in the 1920s and was largely developed by the 1960s and 70s. It describes particles in terms of underlying quantum fields, and combines classical field theory, special relativity and quantum mechanics.

Introduction to Quantum Field Theory: A solid introduction to quantum field theory, intended for final year undergraduates or early graduate students.
Quantum Field Theory: A textbook intended for newcomers to the field. The prerequisites are tough, so it may be advisable to revisit some of the material above if you run into difficulty.
Quantum Field Theory by Sidney Coleman: Lecture notes from Coleman’s 1986 course at Harvard. Videos of his course are also available, though the quality is often rather poor.
The Conceptual Basis of Quantum Field Theory: For those ready to take a deeper look at the Quantum Field Theory, Gerald ‘t Hooft reviews some of the conceptual issues with the theory.
Quantum Field Theory I: From the Perimeter Institute, this online course introduces quantum field theory.
Quantum Field Theory II: The Perimeter Institute goes deeper into quantum field theory in this follow-on course.

Beyond the Standard Model

Quantum theory, along with the Standard Model, is perhaps the most successful theory of physics ever conceived. Yet in one key area of physics - gravity - it is silent. We cannot, therefore, use it to tell us what happens inside a black hole, or in the earliest moments of the Big Bang. For that, physicists will need to move beyond the standard model, into the realm of quantum gravity, supersymmetry and strings. Be aware, much of what you will encounter here is highly speculative, theoretical and, above all, unproven.

Quantum Gravity in Everyday Life: A short look at reconciling general relativity and quantum physics into a theory of quantum gravity.
Supersymmetric Quantum Mechanics: A short course on supersymmetry by David Tong.
Superspace: On supersymmetry. Once highly fashionable, today much less so - especially since the Large Hadron Collider failed to find any evidence to support it.
Introduction to String Theory: String theory may be the future of physics, or it may be a load of unprovable nonsense. Gerald ‘t Hooft offers an introduction to the topic here.
String Field Theory - A Modern Introduction: A second text introducing the ideas behind string theory.
String Theory: From Cambridge University, David Tong provides this course for beginners in string theory.

Astronomy

So far I have focused on the key areas of physics. There are, of course, many branches and subfields of physics, each of which you can spend a lifetime studying in depth. Astronomy is perhaps the oldest of these, as the rhythms of the stars and planets were studied long before the Greeks dreamed up the foundations of what would later become physics.

Astronomy: A free textbook that covers much of our modern understanding of astronomy without a lot of mathematics. A good introduction for those looking for an overview of the subject.
A Practical Guide to Observational Astronomy: This book covers the way in which we actually observe the universe, from charting the positions of the stars to recording the photons coming from them. Good reading for those interested in how we do astronomy.

Introduction to Celestial Mechanics: Celestial mechanics concerns the movements of stars and planets, typically as seen from Earth. It is an ancient subject, once studied to divine messages from the Gods. Today it has found application in the orbits of satellites and spacecraft.

The Fundamentals of Stellar Astrophysics: A slightly old textbook, but one that addresses our understanding of how stars burn and how they are structured.

Principles of Heliophysics: Heliophysics covers the interaction between stars and planets. This textbook delves into how space weather affects planets, and how, in turn, that affects the potential for life on worlds across the galaxy.

High Energy Cosmic Rays: Lecture notes on the origins and types of cosmic rays that bombard our planet from deep space.
Extrasolar Planets: Compiled lecture notes from ETH Zurich covering exoplanets, how they form, and how we can detect them.

Cosmology

Astronomy and astrophysics study the objects that fill the universe: the planets, the stars and the galaxies. Cosmology, by contrast, is the study of the universe itself - how it began, how it evolved, how it is shaped and, indeed, how it will all end.

Introduction to Cosmology: Lecture notes providing an introductory course on cosmology. It is useful to have at least some knowledge of general relativity before starting.
TASI Lectures: Introduction to Cosmology: A somewhat more advanced “introduction” to cosmology. Requires a deeper understanding of general relativity to get the most from it.
Cosmology: From the Perimeter Institute, this online course includes 16 lectures on modern cosmology.

Refer a friend

The Bold Insanity of Artemis II: America Prepares to Return to the Moon - The Quantum Cat

2026-01-31T13:31:43.000Z

On the right the four astronauts of Artemis II. On the left stand their two backups, Andre Douglas and Jenni Gibbons. Credit: NASA/Joel Kowsky.

If NASA keeps the schedule, the moment of lift-off will come in early February. Six immense engines will roar to life, each belching out a tremendous cloud of fire and smoke. Eight point eight million pounds of thrust will be the result, and all of it will force a towering structure upwards, hurling two thousand tonnes of metal and fuel up, up into the sky.

What an acceleration the four people atop this tower will experience! In sixty seconds the engines will have forced them past the sound barrier. A minute later the solid boosters have gone, peeling away and falling back towards the ocean thirty miles below. The rocket burns on, the speedometer races higher, and then – eight minutes and three seconds on the clock – the whole thing falls silent.

That will be enough. By then the capsule will be in orbit, moving fast enough to reach an altitude greater than any astronaut has ventured in the past fifty years. The rocket – price tag two billion dollars – will be spent. It separates, falls back, and plummets towards the floor of the Pacific Ocean.

The capsule flies on, and within an hour it and its crew will reach their record-setting apex. At that point, if all has gone well, another set of engines will fire, this time raising its orbit to an altitude above that of the geostationary belt of satellites. From there the astronauts will be able to view the Earth as a solitary disk hanging in the sky, and they will become the first humans to do this since 1972.

From then on, things slow down. The burn towards the Moon takes place about twenty-four hours after launch. The journey towards it takes another four days. On the sixth day of the mission, the crew will travel beyond the record set by Apollo 13, and become the most distant travellers from Earth in all of history. A few hours later, the capsule will fly slowly over the lunar surface, offering its crew a view from the height of a few thousand kilometres.

Then, the irresistible laws of Newton will pull them home. After another four days of flight they will hit the atmosphere, briefly bounce off it, and then plunge, hurtling through its upper layers at a terrifying four hundred miles per minute. Fortunately, the capsule should be able to take it. The air will slow them, the heat shield will protect them, and within a few minutes they will be descending gently towards the ocean under a canopy of parachutes.

The whole thing is quite mad.

The Shadow of Apollo

The closest precedent to this mission is Apollo 8. Launched in December 1968, that flight took three astronauts – Frank Borman, Jim Lovell, and William Anders – around the Moon. They became the first men to fly into deep space, and the first to see the far side of the Moon with their own eyes.

Artemis II will not be an exact replica of that mission. Apollo 8 stayed and orbited the Moon ten times. The crew of Artemis II are following a simpler trajectory, and will merely loop around the Moon without trying to enter orbit. But the objectives are similar: like Apollo 8, Artemis II will test the ability of the Orion capsule to support life and to carry astronauts far beyond the Earth.

Of the four astronauts on board, three are American – Reid Wiseman, Victor Glover, and Christina Koch – and one is Canadian – Jeremy Hansen. The Americans are all experienced astronauts, having each flown to the International Space Station. But for Hansen it will be the debut of a lifetime: his prior experience is as a fighter pilot in the Royal Canadian Air Force, and he has never been to space before.

During the flight, these astronauts will conduct tests to prepare for future missions. While still in orbit around the Earth they will take the capsule through a series of manoeuvres called “proximity operations”. These will replicate actions the spacecraft would need to do to dock with another object – such as a lunar lander – and will allow engineers to gather data and experience for future missions.

Throughout the rest of the flight, the crew will evaluate the life support systems built into Orion, test its communications systems, and practice taking shelter from solar storms. All of this will be vital for the safety of future crews heading towards the Moon.

Heat Shields and Quarantines

One final test will come as the capsule falls back through the atmosphere. After the re-entry of Artemis I, engineers noticed alarming holes had formed in the capsule’s heat shield. Analysis showed that gases had built up within it, but then hadn’t been able to escape as models had predicted. Instead they had expanded under the heat of re-entry, and the resulting pressure had cracked and broken the shield.

To prevent this happening again, engineers have modified the re-entry trajectory. In Artemis I, Orion first “skipped” off the atmosphere, making a shallow plunge that slowed the capsule but wasn’t enough to bring it all the way down. It was during this period that gas built up. When the capsule then did make its final plunge, this gas heated and expanded.

In Artemis II, the capsule will still make this first shallow dive. But in an effort to reduce the gas build-up, engineers have made this portion of the flight shorter. That means Orion will have more speed to lose in its final fall, and that implies a faster and hotter re-entry. Briefly, indeed, the crew will reach the fastest speed ever attained by humans. But it should, engineers say, be safer this way.

If all goes well, Artemis II will pave the way for more ambitious flights in the future. The Artemis program, as it currently stands, envisions a moon landing before 2028, a space station in lunar orbit by 2030, and a series of missions to the lunar surface throughout the following decade. Much work remains to be done for any of this to happen, but Artemis II is an essential step towards these dreams of future exploration.

The launch window for lift-off opens on February 6. A handful of dates are available in early February, but if the rocket hasn’t gotten off the ground by February 11, the window closes until March 6.

Delays are likely1. Artemis I was delayed multiple times as engineers worked issues on the rocket. This time, with astronauts sitting on top, they are likely to be more cautious still. The crew themselves add constraints: they cannot wait in the capsule for more than a few hours, and they must take time to rest and prepare themselves for flight.

But whenever the lift-off comes, the march towards the Moon has already begun. In mid-January the rocket was rolled out to Launch Pad 39B at the Kennedy Space Center. On the 23rd, the crew entered a pre-flight quarantine. After years of training, their moment is almost upon them.

NASA has already announced a delay until February 8, due to cold temperatures at the launch site.

The Week in Space and Physics: Stars Beyond The Supermassive - The Quantum Cat

2026-01-27T13:31:46.000Z

Artemis II stands on the launchpad. Image credit: NASA/Keegan Barber

Just how massive can a star get?

The Sun makes for a logical starting point. It is big, weighing in at over three hundred thousand times the mass of the Earth. But by cosmic standards, that is merely average. Betelgeuse is about fifteen times more massive. Eta Carinae – a star so unstable it occasionally erupts in spectacular detonations – is five times more massive than even that.

But the most massive star known with reasonable certainty is RMC 136a1, a star of almost three hundred solar masses. Located in the nearby Large Magellanic Cloud, it burns with an astonishing luminosity. Were it located at the distance of Alpha Centauri, it would shine as bright as the full moon in our sky; fortunately, or sadly, it is more than a hundred thousand light-years away and visible only through telescopes.

RMC 136a1 is so big that we struggle to explain how it could possibly have formed. It is about twice the expected mass limit for stars, and so some astronomers think it might be the result of other giant stars colliding and merging. Whatever it was, the star is unlikely to be around for long. At such a mass it must be burning fuel at an incredible pace, and it will probably exhaust its reserves within the next two million years.

This seems to be about the limit of what is possible, at least for the current universe. But astronomers have long speculated that the first stars could have been far larger. Back then, the cosmos contained almost nothing but hydrogen, and the first generation of stars would have been very pure. That could have allowed them to swell to enormous sizes.

Little Red Dots in the early cosmos. Could these be the biggest stars ever made? Credit: Jorryt Matthee et al. 2024

But just how big is a matter of debate. Entering the debate recently, Harvard astronomer Avi Loeb – he of the alien interstellar comet theory – suggested they could have exceeded a million solar masses. That would make them by far the largest stars ever to have existed, and in essence would be like combining an entire dwarf galaxy into a single star.

Each would have begun with a core weighing about ten times the mass of the Sun. This would have pulled in gas and grown at an extreme rate. At some point, which Loeb fixes at about a million solar masses, this accumulation of matter would have come to an end. Why is unclear - Loeb merely says they would have run out of gas to feed on – but at this point the star would cease defying reality and simply collapse into a black hole.

Still, there is some evidence for these stars, he says. The James Webb telescope has spotted mysterious red dots scattered across the early cosmos. All seem to be bright and fairly compact. They might, he argues, be the first generation of stars, each so massive and burning so brightly that their photons have survived a thirteen-billion-year-long trip across the universe.

But there are plenty of other explanations too. They might be giant black holes surrounded by clouds of fast-moving gas and dust. Or they could be “black hole stars”, strange objects powered by a central black hole but still shining immensely brightly. For now, astronomers are still free to speculate. So why not let some imagine they are the biggest and brightest stars ever made?

Artemis II Prepares For Launch

In the past half century, no one has ventured deeper into space than Jared Isaacman. In September 2024, he reached an altitude of fourteen hundred kilometres (almost nine hundred miles) above the surface of the Earth. That, though it does not seem like much, is as far as anyone has gone since the days of Apollo.

Perhaps it is fitting, then, that as head of NASA, Isaacman is now overseeing an effort to break that record. If things go to plan, a rocket will soon launch from the Kennedy Space Center in Florida, blast a capsule towards the Moon, and send four astronauts on one of the most daring voyages of the past few decades.

The crew, which is made up of three Americans and one Canadian, will not set foot on the lunar surface. Instead they will loop around the Moon, passing about six thousand kilometres above its craters and mountains. They will then fly back towards the Earth, and re-enter our atmosphere at the astonishing speed of forty thousand kilometres per hour.

NASA’s Concept for the Artemis II mission.

All this should prove the ability of the Artemis rocket and capsule to send astronauts to the Moon. The next step, to be done sometime in the coming years, is to prove the viability of a lunar lander. For this NASA has chosen to use Starship, a spacecraft under development by SpaceX.

NASA says Starship should demonstrate this ability before 2027, in the form of an uncrewed touchdown on the Moon. If that works, then astronauts will once again set off to the Moon on Artemis III. Once there, they will dock with Starship, transfer to its cabin, and then descend to the surface. NASA, and America’s politicians, are hoping all that can be done by 2028.

A Failed Galaxy

Modern models of cosmology say the universe should be full of dark matter halos. In many cases these surround galaxies: the dark matter came first, astronomers say, and then through the force of gravity it attracted normal matter in the form of hydrogen and helium. Later, that matter collapsed into stars, and so the first galaxies were born.

But these same models also say small halos of dark matter should be scattered around the universe. These would still attract normal matter, but not in the volumes needed to form galaxies. In theory, these halos should look like clouds of hydrogen gas, perhaps illuminated by a few scattered stars.

In practice, detecting such things is hard. But in recent years the FAST radio telescope in China has found signals coming from a few isolated clouds of hydrogen. One, located about fourteen million light-years away and named Cloud-9, looks especially interesting.

When it was first spotted, in 2023, astronomers noted it as a possible dark matter halo. But their telescopes lacked the power to spot faint stars, and so they could not rule out the possibility that this was just a small galaxy full of stars we could not see.

Not much to see… Radio images (in purple) show the cloud, but there are few stars within it. Credit: Science: NASA, ESA, VLA, Gagandeep Anand (STScI), Alejandro Benitez-Llambay (University of Milano-Bicocca); Image Processing: Joseph DePasquale (STScI)

Now Hubble has taken a closer look. Its observations have made it clear that this is not a galaxy. There are few stars within it, and instead Cloud-9 looks rather like the long-imagined cloud of gas surrounded by a halo of dark matter.

Within it are about a million solar masses of gas – far too little to spontaneously collapse into stars. This is far outweighed by the mass of dark matter. Astronomers estimate there is about five billion solar masses of the dark stuff holding the cloud together.

The First Private Space Station

Last week Vast Space, an American startup, said it hopes to launch its prototype space station early in 2027. Though in effect a demonstration mission, the space station will be capable of hosting small crews of astronauts for two weeks at a time.

That is not much, especially when compared to the International Space Station. But as Max Haot, the CEO of Vast, said in an interview with Ars Technica, it offers an opportunity for the company to prove it can safely host astronauts in orbit.

That may help them win future contracts from NASA. As the ISS is scheduled to deorbit in the early 2030s, NASA wants commercial partners to manage future stations in orbit. If that works out, NASA would simply pay them to put their astronauts on board, much as they now pay SpaceX to launch them into space.

How well this will work in practice remains to be seen. Though several companies have talked about building private stations, actual progress has been slow. If Vast can launch next year, and if their station can host crews of astronauts, they will place themselves well ahead of the competition.

The World According to Aristotle - The Quantum Cat

2026-01-25T13:31:06.000Z

Charles Laplante, 1866

As nature therefore makes nothing either imperfect or in vain, it necessarily follows that she has made all these things for men
~ Politics, Aristotle

Aristotle was the student of Plato; Plato the student of Socrates.

For twenty years, Aristotle studied at Plato’s Academy. By all accounts, the two got along: Plato nicknamed him the “mind of the school”, and seems to have regarded him as the most promising of all his students.

In this academy, Plato taught of abstract realities, of ideal forms and of utopias. He believed our world was messy, but that underneath it lay a perfect reality hidden from casual view. One could probe this world to uncover Truth, but to do so one had to look inwards. Only through logic and reason, Plato argued, could we understand the nature of reality.

His greatest student came to disagree. Loyalty may have kept him at the academy, and perhaps kept his mouth shut too, but after Plato died, Aristotle began speaking of alternative ideas. He doubted the existence of Plato’s hidden world. Instead, he started to believe that the understanding of nature could only begin with observation.

Aristotle thus observed. His range was astonishing, and stretched far beyond what we would call physics or even science. He wrote about logic, explored the nature of reality, studied biology, and opined about happiness. He travelled greatly, roaming across Anatolia and Greece, and eventually was summoned to the court of Philip II in Macedonia.

There he was appointed tutor to Philip’s thirteen-year-old son Alexander. What he taught him remains unknown – the only book on the subject, Rhetoric to Alexander, was almost certainly written by someone else. But it was probably good: within the next two decades Alexander would become king, conquer the empires of Persia and Egypt, and march his armies into India.

While Alexander was off conquering the world, Aristotle returned to Athens. He founded his own school, the Lyceum, and gave the lectures for which he is best known today. Alexander sent back samples of plants and animals from across his empire, and Aristotle collected and sorted them. Yet, as the conqueror grew more powerful and convinced of his own divinity, Aristotle seems to have grown concerned about what his former student was doing.

The Debris of Creation: Hubble Watches Worlds Collide - The Quantum Cat

2026-01-22T13:30:34.000Z

Fomalhaut and its outer ring of dust. Images combined from the ALMA observatory and from Hubble. Credit: ALMA (ESO/NAOJ/NRAO). Visible light image: the NASA/ESA Hubble Space Telescope

As always, welcome and thank you for reading! For those who are new here, this is a newsletter on space and physics. This week, paid subscribers will get an additional post on the physics of Aristotle. For full access to this and to our full archive, you can become a paying subscriber here.

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The spectacular cloud of dust and debris around Fomalhaut has long been a favourite target of astronomers. After all, the star is one of the brightest and closest of the southern sky, and its debris cloud makes for good photos. Those taken by the James Webb Space Telescope capture glowing rings looping around the star; those from Hubble show a bright outer ring encircling inner debris fields as if to create a cosmic all-seeing Eye of Sauron.

Since the star is around half a billion years old – young, as these things go – this cloud is thought to be a disk of rock and dust slowly coalescing into planets. Its inner rings, imaged by the James Webb, might already be shaped by the passage of large planets sweeping around the star. The outer ones, seen by Hubble, are probably home to countless dwarf worlds known to astronomers as planetesimals.

In 2004, headlines were made when Hubble spotted something that looked like a planet in those outer rings. The discovery was hailed as a big success: indeed, it marked one of the first times we thought we had taken direct images of a world around another star. But things soon got weird. In optical wavelengths the object was far brighter than any planet should be, yet when telescopes examined it in infrared wavelengths they failed to spot anything at all.

How to explain this? Some astronomers clung to the idea it was a planet. But to salvage the big discovery, they had to wrap it in a thick cloud of dust. If this layer existed, they argued, it would reflect starlight and make the world look far brighter than it otherwise would. Others pointed out that the planet itself was unnecessary. Instead, they said, we may simply be seeing a cloud of debris formed by a violent collision between worlds.

In the decades since, the evidence has mostly favoured the second idea. When Hubble revisited Fomalhaut in the early 2010s, it found the object expanding and fading in size, just as a debris cloud might be expected to. Even more convincingly, it seemed to be moving radially away from the star. That would make sense if grains of dust were being blown outwards under the radiation pressure of the star, again as might be expected after a collision.

By 2014, the object had vanished altogether, and it has remained elusive ever since. In 2023 astronomers led by Paul Kalas of the University of California searched for it again. Once again they used Hubble, but, as they outlined in a recent paper, they still couldn’t find any clear sign of the dust cloud. Yet as they searched, they did find something else: a new point-like object had appeared around Fomalhaut.

Images of the two “planet” like objects seen around Fomalhaut. Both are probably the aftermath of violent collision between worlds, rather than planets themselves. Credit: Kalas et al. 2025.

When Worlds Collide

The idea that small planets might be smashing into each other is not particularly surprising. Fomalhaut is a young star surrounded by a large and chaotic cloud of debris left over from its formation. Within it, chunks of rock and ice are moving, accumulating mass, and trying to sweep their orbits clear. This is how star systems form, and eventually it may well settle down to become a calm and respectable system like our own.

But right now, things look far from ordered. Orbits are still in conflict, and sometimes big things crash into each other. On most occasions these are minor events, part of the natural gathering of matter. But at other times they are cataclysmic: two small worlds smash into each other at speed, the violence of the collision shatters them, and a great cloud of dust and rocky fragments takes their place.

This probably describes both events that we have now seen. Surprisingly, however, the objects are unlikely to be large. We are not watching planets like Venus crash into Mars, according to Kalas and his team, but instead seeing collisions between large asteroids or prototype worlds.

The logic behind this is simple: big planets must be few in number, and collisions between them must be rare. It is unlikely we would have witnessed two such events in the past few decades. Instead, it is more reasonable to say we are seeing collisions between dwarf planets or large asteroids. These objects should number in their millions, and a big impact could come roughly once every few dozen years.

But the authors also see hints that more is happening than we currently know. The new object appeared close to the site of the previous one, which seems like an odd coincidence. It is possible, Kalas says, that rings of debris happen to cross at this point, though the observations we have so far seem to contradict this idea. Another option, he writes, is for an unseen planet to be herding smaller worlds into this particular region.

These debris rings may also be shaped by the two small stars that orbit Fomalhaut. Both are quite distant, and will not normally disturb the system. Yet at times they do sweep inwards, and their gravitational pull is bound to have some effect. Indeed, the stars may sometimes direct small planets onto collision courses, and thus help instigate bouts of chaos.

On the left, Fomalhaut and its outer ring. On the right, a model of how the first dust cloud expanded and faded. The new cloud may be expected to show the same in the coming years. Credit: NASA, ESA, and A. Gáspár and G. Rieke (University of Arizona)

Under Heavy Bombardment

We do not have to look far to find evidence of similar events elsewhere. Craters on our own Moon tell of a cataclysmic period long ago when the Earth and its satellite were bombarded by asteroids and comets. Where these came from is still uncertain, but several theories pin the blame on the outer edges of the solar system.

In one model, the gas giants – Jupiter, Saturn, Uranus, and Neptune – fell into a gravitational resonance. Saturn may have been flung outwards; indeed, some simulations suggest it was born closer to the Sun than Jupiter was, and that the planets swapped place in a moment of violence. The outward swing of Saturn unsettled Uranus and Neptune, and might even have sent a fifth gas giant careening outwards.

If so, that extra planet has long been lost, and now floats alone in the galaxy. But its movements, or those of the other gas giants, pushed the cloud of ice and rock at the edge of the solar system into chaos. Collisions would have been frequent, and a rain of asteroids would have fallen on the inner planets.

Today, of course, things are much calmer. The planets follow regular, well-swept orbits. The asteroids have mostly been herded into groups, and collisions between things are now rare. But this might not last forever. Models show our solar system is still a chaotic system. A small disturbance – perhaps the approach of another star, perhaps the wandering of a stray comet – could throw things off balance.

If that happens, simulations cannot accurately predict the outcome. Models show different catastrophic possibilities: a planet could plunge into the Sun, Mercury could smash into Venus, or Mars could be hurled out into interstellar space. Fortunately, all these scenarios take tens of millions of years to play out, and so we’d get plenty of warning of the impending chaos. And with that, hopefully, we would have time to do something about it.

Project Mercury and the SOFAR Bomb - The Quantum Cat

2026-01-16T15:31:22.000Z

The flight of Alan Shepard. Credit: NASA

Project Mercury was supposed to be fast, and it was supposed to be simple. After all, Sputnik had made it starkly clear the Soviets were ahead, and America feared falling even further behind. The newly created NASA quickly struck back with Explorer 1, launched less than four months after Sputnik, but by then the Soviets had put a dog in space and everyone knew a human would be next. To have any hope of getting there first, Mercury had to be as fast and as simple as possible.

Except, of course, that putting a man into space for the first time was anything but simple. First you needed a rocket, and the ones America had in 1959 still had a nasty habit of blowing up. Then you needed a capsule – and this was supposed to be dumb, just something a person could sit in for a few hours and sail safely through the vacuum of space. And then you needed to bring him back to Earth.

For this last bit, America chose to use the oceans. To return to Earth, an orbiting capsule first needs to fire its thrusters, a burn that slows the capsule and drains it of the energy needed to remain in orbit. After that it will fall, and if you time the burn correctly, it will descend towards a chosen spot on the ground. Put that spot in the ocean, and things are simpler: water is more forgiving than solid rock, at least when it comes to things falling at high speed.

But afterwards things can be complicated. A capsule must float; it must be able to survive waves and whatever else the weather throws at it; and it must be able to be found. And none of that is especially easy. In Project Mercury one of the capsules sank, a disaster which almost took an astronaut with it, and two others came down hundreds of miles off course, each invoking a search over vast stretches of the ocean.

This was a time before the navigation systems we rely on today. There was no constellation of GPS satellites, and no network of relay satellites to transmit distress calls. The deep ocean was vast, mysterious, and largely out of reach. If a capsule came down five hundred miles short of its target, as one of the first test flights did, then finding it was akin to looking for the proverbial needle in a haystack.

What was needed was a way to locate capsules amidst the waves. At first, uncertain of what would work, NASA threw almost everything they could at the problem. An armada of ships and aircraft were scattered across the ocean before every flight, and the capsules themselves were fitted with an array of aids to assist in finding them. They scattered chaff as the parachutes opened, hoping it would appear on radar, triggered radio beacons on splashdown, and dropped bombs that would explode deep under the waves.

From Patent US3093346A: Space Capsule

This last idea, that of the SOFAR bomb, relies on an oddity of the deep oceans. There, roughly a kilometre below the surface, lies a sound channel. If a bomb can be detonated there, the sound of it can be picked up thousands of miles away, and that offers a way to hone in on the position of whatever has dropped it.

The reasons why this works are subtle. First, of course, is the simple fact that sound travels more easily through water than through air. That makes logical sense: sound moves through the vibrations of particles, and those particles are more closely packed in water than in air. This also means sound travels faster through water than it does through air: the speed of sound in fresh water at room temperature, for example, is four times that in air.

The speed of sound in water, however, also depends on both pressure and temperature. In colder water sound travels more slowly. The deeper under the surface of the ocean you go, the colder things normally get, and so if all else is equal, sound waves moving deep under the waves should travel more slowly than those near the surface.

But, as always, things are not equal. The deeper into the ocean you go, the more water you have pushing down on you, and the higher the pressure you experience. As pressure increases, sound travels faster. Initially, as you descend under the waves, the change in temperature dominates and sound slows down. But at some point, approximately a thousand meters deep, pressure begins to assert itself, and sound speeds up again.

This creates a minimum, a distinct depth at which sound waves reach their slowest speed. If a sound originates here, it will stay here. If it rises, it will be reflected down. If it falls, it will be pushed back up. The only way it can move is within the layer itself, horizontally under the waves.

This implies two things. First, that sound waves cannot enter this layer. Only what is made within it can be heard by someone else listening inside it. And second, that sound waves cannot leave: any noise originating within this layer can thus be heard at enormous distances. Whale song is a good example of this: it can travel across an ocean, and allow a creature off the coast of Ireland to communicate with another swimming near Virginia.

The SOFAR channel, illustrated by NOAA.

We have developed two easy ways to create sounds underwater. One is to drop a hollow metallic sphere. At the right depth and pressure it will be crushed and the sound of the implosion will echo through the underwater channel. The other – the method used on Mercury – is to drop a bomb, use a pressure sensor to trigger a detonation, and then wait for the sound wave to travel through the water.

Each of the early Mercury capsules carried two such SOFAR – SOund Fixing And Ranging – bombs on board. One was stowed with the parachutes, and would be thrown out as they deployed. It would fall in the ocean and give any waiting ships a bearing upon which to look for the spacecraft.

The other was stowed within the capsule itself, and would only detonate if the whole thing sank. This would send a second location pulse to ships. But the explosion was also intended to destroy vital components inside the capsule, and thus prevent the Soviets from ever retrieving American designs.

Both bombs had a range of about three thousand miles. Hydrophones installed as part of Cold War efforts to track submarines could listen for them, as could vessels equipped with listening equipment and special buoys dropped by aircraft. All that gave the Navy plenty of points with which to triangulate the signal.

A Mercury capsule afloat while the Navy practices recovery operations. Credit: NASA.

On September 9, 1959, all this was put into practice. Big Joe I, an uncrewed test capsule, was launched from Cape Canaveral. Things did not go to plan. A few minutes into the flight, the booster failed to jettison. That made everything heavier than it should have been, and to compensate the engines burned longer. Yet it wasn’t enough. When they ran out of fuel, the spacecraft was still coming in too steep. It landed five hundred miles short of its target.

But everything worked: the chaff deployed, an automatic radio beacon was picked up by a nearby aircraft, and the bomb exploded deep under the water. It took less than two hours to confirm the capsule’s location via the SOFAR channel, and the recovery operation itself was done within eight.

Overall, however, SOFAR proved less useful than hoped. The Navy often took hours to process the data from its microphones, and even then the results would reflect the point at which the parachutes had opened rather than the actual location of the capsule. When Mercury-Atlas 7 splashed down two hundred miles off-target, it was the radio beacons that first alerted search crews, not the bomb.

These difficulties, along with the effectiveness of radio beacons and water dyes, spelled the eventual end of the SOFAR bomb. After the fourth manned flight, NASA decided to drop both the bombs and the chaff. They were not used again on Mercury, nor on Gemini or Apollo. The Shuttle, of course, had no need for them, and by the time American capsules started splashing down in the oceans again, global positioning satellites had rendered all other techniques unnecessary.

Yet the bomb is a testament to a time when spaceflight was new and engineers were unafraid to think creatively. Project Mercury had to be fast, and there was no time to run years of analysis to prove what would work or what wouldn’t. Engineers were pragmatic, they tried new things, and if they proved unnecessary they weren’t afraid to move on.

True, not everything went right. There were near misses, close calls, and moments that could easily have ended in tragedy. But Mercury did succeed in putting a man into space, even if the Soviets were first by a month. And for a brief time, the sounds of those bold missions echoed through the depths of the oceans, accompanied by the songs of the whales and the mechanical whirr of the submarines.

The Week in Space and Physics: A Private Hubble - The Quantum Cat

2026-01-13T13:31:42.000Z

Engineers work to connect the inner and outer segments of the Nancy Grace Roman telescope. Credit: NASA/ Sydney Rohde

For the past decade, NASA has had a large mirror sitting in a warehouse. In principle, it could one day form the centrepiece of a new Hubble-class telescope. But in reality, money is short. NASA has the technology to build such an observatory, and plenty of ideas for what to do with one, yet sadly the political desire to fund such a project has long been missing.

Could America’s billionaires fill that gap? They have the cash, the rockets, and a few, it seems, also have the will. Last week two of them, Eric and Wendy Schmidt, announced they would fund a set of powerful astronomical observatories. The centrepiece of their investment is a space telescope they call Lazuli, an observatory of greater power than Hubble they hope to place in a high orbit over the Earth.

Eric Schmidt was an early CEO of Google. He is now fantastically wealthy, and he and his wife have set up a series of foundations intended to encourage scientific work. It is one of these, Schmidt Sciences, that has decided to fund the observatories, a project that seems likely to cost more than a billion dollars in total.

Four astronomical centres will be funded. The first, the Argus Array, will study the sky in optical frequencies – those visible to the human eye – and will be suited for spotting rare events like supernovae. Another, called the Deep Synoptic Array, will observe radio frequencies. A third, LFAST, will act as a scalable prototype that could, if expanded enough, gather as much light as some of the largest telescopes now under construction.

Credit: Roy et al, 2025.

It is the space telescope, however, that has captured the most attention. Schmidt Sciences propose to build and operate an observatory with a bigger mirror than Hubble’s. It will be equipped with more advanced instruments, and will orbit at a much higher altitude. It is, Schmidt Sciences said, a modern realisation of Hubble-like capabilities.

If this announcement were coming from NASA or ESA, it would not be surprising to hear that operations will not start until the late 2030s. But Schmidt Sciences reckon the telescope can be in orbit by 2029. That is fast. And if it can be done, it will be a major boost to the world’s astronomical abilities.

Although it is rare today, historically many observatories were funded by wealthy patrons. A few examples may still be found, but nothing of this scale has ever been attempted by private organisations. Yet in a world where government money can be scarce and in which budgets can be held hostage by politicians, new funding sources and alternative models for astronomy are to be welcomed.

Isaacman Takes Charge at NASA

After a tumultuous nomination process, Jared Isaacman is now in charge of NASA. The billionaire and private astronaut was first proposed for the job at the end of 2024. But he was brushed aside after Donald Trump and Elon Musk had a spectacular, if rather childish, falling out. After they repaired their relationship his name was raised again, and he was confirmed by the US Senate on 17 December.

His start at NASA has been eventful. Last week, as astronauts on the space station prepared for a space walk, one of them made an urgent call to ground controllers in Houston. Exactly what happened is not yet clear, but it appears some kind of medical situation developed. NASA has said it was not an injury and that the astronaut is stable, yet it was serious enough to postpone the planned excursion.

After conferring for a few days, NASA then decided to return the astronaut and crew to Earth early. Details of the medical situation, and the astronaut in question, have not been released – indeed, NASA typically goes to great lengths to protect the privacy of their astronauts, and it may not ever give the full details of what exactly has happened.

Though plans for medical evacuations have been in place since crews first set foot on the station, this is the first time they have been put into action. The early departure of the four astronauts, which should take place on Wednesday, will leave a minimal crew of three onboard the International Space Station.

SpaceX’s Dragon capsule seen out of the window of the ISS. Credit: NASA.

Alongside that, NASA is moving ahead with plans to launch Artemis II, the first crewed flight beyond low earth orbit since the days of Apollo. Four astronauts will travel in the Orion capsule over a ten day mission that will take them around the Moon. They will not set foot on the lunar surface, but they will become the closest visitors to our natural satellite since 1972.

There are, however, questions about the safety of Orion’s heat shield. Examination of the shield after Artemis I, an uncrewed test flight, found it had behaved in unexpected ways.

Engineers have modified the planned re-entry trajectory to minimise the risk, but some are still concerned about whether it – and the crew – will survive their fiery plunge back to Earth. After examining the data, however, Isaacman declared he was satisfied with the proposed approach. NASA is now working towards a launch window opening on 6 February.

Does Siwarha Really Exist?

Betelgeuse is one of the brightest stars in the sky. At first glance it seems to be alone, but for a long time we have suspected it has a hidden companion. Fluctuations in the star’s brightness show a regular pattern, as if something is tugging on it in a periodic way, just as another star in orbit around it might do.

Yet observations have so far failed to spot any companion. Some measurements have hinted at one – a study last year, for example, claimed to have seen it – but all have been inconclusive. Now, for the first time, astronomers looking at data from the Hubble Space Telescope claim to have found evidence of a wake left behind this companion star.

An artist’s conception of what the wake behind Siwarha may look like. Artwork: NASA, ESA, Elizabeth Wheatley (STScI); Science: Andrea Dupree (CfA)

Models suggest the star, which has been named Siwarha, orbits so close to Betelgeuse that it should lie within the giant star’s outer atmosphere. As it moves through this layer it ought, therefore, to leave a trail of disturbance behind it.

After examining Betelgeuse carefully over the past decade, the astronomers say they found multiple signs of such a trail rising and falling over a six year cycle. That matches well with other observations about the periodic nature of Betelgeuse, and should be taken as new evidence supporting the existence of this companion star.

As always, caution is needed. Light from this star has not yet been definitely spotted, and right now the models say it is behind Betelgeuse and cannot be seen. It should re-emerge in 2027. When it does, telescopes are bound to be watching for it. If the growing pile of evidence is correct, someone may be able to claim a discovery by the end of next year.

The Roman Telescope

NASA announced the successful completion of construction work on the Nancy Grace Roman Space Telescope. The final step came at the Goddard Space Centre in Maryland, where engineers connected the inner and outer segments of the new observatory.

Like the James Webb Space Telescope, Roman is designed to study the sky in infrared light. But unlike the James Webb – which often looks deep into small areas of the cosmos - Roman is equipped to study wide areas simultaneously. This will allow astronomers to study swathes of the sky, and so to look for things like supernova, exoplanets, and the effects of dark matter.

The telescope will now go through a period of final testing. By the summer it will be delivered to the launch site, and there the final preparations for lift-off will take place. The launch date itself is still to be determined, but NASA and SpaceX say it could come as soon as October.

Issue No. 350 - The Orbital Index

2026-01-07T00:00:00.000Z

The End of The Orbital Index

Issue No. 350 | Jan 7, 2026

🚀 🌎 ✌️

When we started The Orbital Index, Ben was working at an early-stage VC, and Andrew had just taken his first job in aerospace, building smallsat ground control software at a tiny startup called Kubos. The newsletter was a way for us to learn a new industry, a product design exercise, and a shared experiment in science communication and concise curation by two very long-time friends.

Since then, Orbital Index has developed its own voice and an avid following. Sarajane joined as our incredible assistant editor, and we somehow managed to publish nearly every week for almost seven years.

During those seven years, Andrew journeyed from industry outsider to a founding role at Vast and, later, to co-founding space solar energy startup Overview Energy. Ben used the newsletter as a vehicle to explore space deeply and develop the discipline of writing concisely and clearly—making mission concepts and rocket engine specs understandable without losing technical depth, all while writing significantly more than any of his English teachers ever thought he should.

The space industry has changed a lot during Orbital Index’s tenure. When we started, New Space was, well, new. The first privately funded lunar lander, SpaceIL’s Beresheet, had just launched; Opportunity’s mission had just ended, with Perseverance on the horizon; SpaceX’s Crew Dragon had yet to carry people into space; Starhopper hadn’t hopped and only two Starlink prototypes had flown; the Chinese Space Station hadn’t launched, nor had any of China’s ambitious sample return missions; and, not one commercial Chinese rocket had reached orbit.

Fast forward, and the landscape is dramatically different today. Commercial companies are exuberantly undertaking almost every aspect of space that used to be purely governmental. These ambitions will soon be bolstered by the arrival of significantly lower-cost launch on reusable launch vehicles from across the US, China, and, eventually, Europe.

The next decade of space is going to be incredible, and we’re excited to be involved in our own ways, but the amount of time and attention required to do it justice in a newsletter has grown beyond what we can muster alongside families, careers, and commitments. We both find ourselves at moments of transition, more burdened than energized by the weekly task of writing, and feeling ready for change, with our attention on new horizons and adventures. And so, as bittersweet as it is, this is our 350th and final issue of The Orbital Index.

In this last omnibus issue, we’ll share our incomplete view of where we see the space industry heading in the next decade.

✧✧✧

¶Private everything. It’s been clear for a while that, step by step, space is joining the domain of private enterprise. Corporations dominate launch, telecommunications, and much of Earth observation. Companies are now actively working on replacing governmental efforts with commercial offerings in space situational awareness, comms (including deep space), cislunar transport (more below), positioning and navigation, and some remaining niches of Earth observation (fire monitoring, CO2 monitoring, and more… but some EO may remain a poor fit for commercial ‘science-as-a-service’ business models). At least in the West, the next space stations will be commercial, as will transport to them. To be clear, this is only possible because of government support for the ISS over the last 30 years and additional funding through NASA’s CLD program. Similarly, NASA’s CLPS contracts have set the stage for increasingly commercial lunar missions. Beyond cislunar space and in the astrophysics and astronomy domains, most missions under development remain national, but that too is slowly changing. Rocket Lab and MIT's Venus Life Finder mission, and a new crop of asteroid mining startups, are slowly pushing the commercial sphere outward. Meanwhile, private non-profit efforts are quietly working on space telescopes, both big ones and somewhat smaller, cheap and mass-produced ones designed to revolutionize the questions that space science can ask. Enabled by the prospect of dramatically lower launch costs courtesy of Starship and New Glenn, private companies are also working on efforts that have no operational governmental analogues, including power beaming, orbital data centers, orbital refueling, in-space manufacturing, and orbital assembly. Like it or not, capitalism seems to be actively heading toward ~~new capital markets~~ the stars.

Rocket Lab and MIT’s Venus Life Finder mission, approaching Venus sometime in 2027 or later, to probably not find life.

¶We hope the Moon likes rovers… cause it’s getting a lot. As lunar exploration ramps up worldwide, our celestial companion is slated to be explored by increasingly advanced rovers over the next 10 years. ⚙️

Small but mighty: Building on its first successful CLPS Moon landing, Firefly’s next three CLPS landers this decade will all carry rovers: UAE’s Rashid 2 on the second lander, Honeybee Robotics’ first rover on the third—exploring a unique lunar volcano—and on the fourth mission, both Astrobotic’s versatile CubeRover and Canada’s first rover. NASA has also awarded future contracts for Astrobotic CubeRovers to demonstrate power transmission and lunar night survival. This year, Intuitive Machines’ third Moon landing attempt will carry NASA’s Lunar Vertex instruments on the lander along with a rover to study a magnetic swirl, helping us understand the Moon’s evolution. This lander will also deploy NASA’s three CADRE rovers, which collectively will autonomously map the surface and subsurface around Reiner Gamma. ispace US’s first CLPS mission through Draper in 2027 will carry a demonstration rover from the company’s European arm. China’s Chang’e 8 lander will deploy Pakistan’s first rover and two small mobile bots from private Chinese company STAR.VISION. Future Artemis IV astronauts will also deploy a rover, built by Lunar Outpost, which will study lunar dust and surface plasma. And finally, Australia’s first rover, called Roo-ver, will launch by 2030 on an as-yet-unidentified CLPS lander to explore water ice at the south pole.
Sophisticated: Launching this year, China’s Chang’e 7 rover and hopper, carrying a comprehensive instrument suite, will map and characterize water ice and other volatiles on the Moon’s south pole, crucial for planning sustained crewed and robotic missions. Later this decade, a Chang’e 8 rover and dextrous mobile robot will comprehensively study the south polar geology & environment while also building lunar soil-based structures. Astrobotic’s Griffin CLPS lander will deploy Astrolab’s semi-autonomous FLIP rover on the Moon’s south pole later this year; it got manifested last year after NASA decided not to fly the critical VIPER rover for studying water ice. NASA has now tentatively chosen Blue Origin’s second Mark I lander to hopefully fly VIPER in 2027. The joint ISRO-JAXA Chandrayaan 5/LUPEX rover mission later this decade will drill and analyze south polar water ice, and can provide NASA with critical data that is currently missing in Artemis planning.
Crew support: China is progressing with prototypes of a small crewed rover as part of its ambitious plan to land humans on the Moon by 2030. NASA, meanwhile, plans to have a cutting-edge Lunar Terrain Vehicle being used by Artemis astronauts across missions starting at the end of this decade. JAXA will provide NASA with an even more advanced rover next decade, which will be pressurized, enabling astronauts to spend weeks exploring in it. In return, NASA has agreed to land two Japanese astronauts on the Moon.

— Contributed by our friend Jatan Mehta. For an expanded rundown of these rovers, read Moon Monday #256.

An illustration of Japan’s upcoming pressurized crewed rover for NASA Artemis. A large solar panel covers the other side. Credit: JAXA/Toyota

¶Future of Cislunar Transport. Cislunar space—a 550,000 km-radius spherical region governed by the combined gravitational influence of the Earth and Moon, including the five Earth–Moon Lagrange points—is poised to see a sharp increase in activity as lunar ambitions shift from short-duration visits to sustained presence. Driven largely by U.S. and Chinese programs, more than 100 missions are already planned for the Earth–Moon system over the next decade, spanning science, infrastructure, communications, and national security. This growing cadence is pushing cislunar space to host a transportation network rather than merely being a destination, shaped by its relatively low energy cost to access and the operational demands of heavier Earth–Moon traffic. From a delta-v standpoint, injecting payloads onto cislunar transfer trajectories (~3.2–3.9 km/s from LEO) is comparable to reaching geosynchronous orbit (~4.1–4.3 km/s), but once there, spacecraft must operate reliably within the dynamics of the three-body system, contend with a weak and irregular lunar gravity field, and actively maintain unstable orbits such as near-rectilinear halo orbits (Gateway will be in an L2 NRHO if it actually launches). These conditions make cislunar space an ideal environment for maturing in-space transport capabilities, forcing a transition from single-use missions toward sustained mobility. Future architectures increasingly rely on reusable transfer vehicles, space tugs, and logistics platforms capable of repeated rendezvous, continuous station-keeping, and multi-year operations—capabilities already implicit in the logistics requirements of NASA’s Artemis program and Lunar Gateway, as well as China’s Chang’e-derived lunar infrastructure roadmap. NASA recently funded initial studies into low cost commercial platforms such as Blue Origin’s Blue Ring and Impulse’s Helios kickstage toward a model in which cislunar transport functions as a service, moving spacecraft between Earth orbit, lunar orbit, and interplanetary departure points. These systems demand reusable propulsion, long-duration operation, and flexible mission profiles. In contrast, DARPA’s (surprising) decision to cancel the DRACO program (c.f. Issue № 229) highlights the near-term prioritization of chemically- and electrically-propelled architectures over higher-risk nuclear thermal propulsion. In the emerging cislunar architecture, the central technical challenge is no longer reaching cislunar space, but operating reliable, repeatable transportation systems within it—establishing the logistical backbone required for sustained lunar operations and eventual missions to Mars and beyond.

— Contributed by Sarajane Crawford, our amazing assistant editor for the past 3 years.

A diagram showcasing the varying orbits and subsequent use cases available in cislunar space, highlighting the need for flexible transport options.

¶So many more rockets. In the seven years we’ve been writing Orbital Index, the commercial launch sector has seen the first few vehicles reach space from companies founded this century. But the NewLaunch world, imagined as a bustling marketplace featuring a plethora of launch providers vying for market share, driving costs lower, and consistently launching, has largely failed to materialize. Falcon 9 and Electron remain the only new, non-governmental vehicles with truly mature flight heritage, and they have only recently been joined by New Glenn, Firefly Alpha (with its recent mixed record), Vulcan, and Zhuque-3, all with single-digit successful launches. However, waiting in the wings is a growing cadre of will-definitely-launch-in-the-next-two-years rockets, which have almost become too numerous to track (ed. actually, it’d be great if someone built a web app to track all of them—but until then, there is a lovely list of all the small launchers). Here’s a partial list in rough order of our best guess of the likelihood of the next vehicles to successfully reach orbit sometime kinda-sorta-soonish: Starship (wenorbit?), Neutron (recent fairing test), Stoke Space Nova, Relativity Terran R (recent update video), Gilmour Eris Block 1, Hanbit-Nano, Isar Spectrum, Space One Kairos, RFA One, Orienspace Gravity-2, Northrop/Firefly Eclipse, Interstellar Zero, Skyrora XL, Space Pioneer Tianlong-3, Galactic Energy Pallas-1, Orbex Prime, PLD Space Miura 5, MaiaSpace Maia, i-Space Hyperbola-3, Skyroot Vikram-1, Deep Blue Nebula-1, and Astra Rocket 4. Several of these could be ranked higher, but don’t have publicly manifested non-governmental customers, meaning they’ll be slower to become truly ‘commercial.’ Our opinion is that reusability will, unsurprisingly, be the biggest determining factor in the business success of these rockets once they make it to orbit, mitigated in the near-term by vehicles with strong government contracting success.

¶ Space science. Over time, the availability of low-cost launch will rewrite the manual for space science, just like everything else in orbit. Lower costs enable iteration and scaled production, allowing mission designers to take more risk and adapt standardized interfaces to their own science questions (a la Cosmic Frontier Labs, linked above). These platforms will replace some of the exquisite, failure-is-not-an-option missions of today, along with their astronomical price tags. Blockbuster missions, though, will still have a place, and many are in the works, even despite the current US Administration’s dislike of science and active threat to ~41 space missions—some late-breaking good news here, though. NASA is still officially pursuing Dragonfly, the Roman Space Telescope, and several others, although much remains uncertain. Meanwhile, the rest of the world has been and will continue to be stepping up, especially ESA (we’re excited for Comet Interceptor, PLATO, ARIEL, EnVision, eventually LISA, and a load of important Earth science missions) and China (missions to the Moon, Mars, asteroids, and later Jupiter, and maybe Uranus and Neptune). There are also ambitious Korean, Japanese (MMX!), Indian, and Emirati missions. As mentioned above, we also expect more private deep-space and science missions over time. It’s clear that science isn’t going to wait around for NASA, and we’re also quietly optimistic that, under the new leadership of Jared Isaacman, NASA will be back in the game sooner than many of us feared. 🤞 🔭

ESA and JAXA’s Comet Interceptor approaching an unknown future comet (or interstellar object?) after having loitered in space waiting for its unsuspecting prey and a moment in the sun.

¶Space and Earth: the decade ahead. The next decade is vanishingly small on the timescale of planets, but it is likely to be a critical one for humanity, with space playing its own crucial role. And while the current US administration is pushing to cut Earth Science programs, personnel, and missions (both in development and operational; c.f. recent NCAR shutdown news), that doesn’t change the fact that modern climate science emerged in part from the truly global vantage point provided by our ability to put people, cameras, and sensors in orbit. While budgets are under fire at NASA/NOAA/USGS/etc, much of the rest of the world seems to understand that this work remains existential. ESA has more Earth Science missions in development and operation than ever before (we’re particularly excited for FORUM, Copernicus CO2M, and FLEX), JAXA is staying the course on its own small set of missions (ISS-hosted MOLI and PMM), China is beginning to add its version of Earth Science missions (TanSat-2 and DQ-2), and multiple smaller nations have missions in progress (Canada’s WildFireSat, Norway’s AOS-P, and South Korea’s recently launched KOMPSAT-7). These missions and the data they’ll produce are critical, as humanity is blowing past its +1.5 ºC warming limit after a decade of record average global temperatures and mounting climate-induced disasters. These realities firmly place us in uncharted territory; we don’t know how quickly or how drastically climate patterns will shift as a result, particularly given our limited understanding of climate tipping points that will likely accelerate warming (if you like board games, Daybreak is fun and our favorite that includes tipping points). Our ability to mitigate atmospheric methane and its sources (leaks, flaring, etc.); understand cloud behavior at particle, single-cloud, and weather system scale; measure carbon cycle components like biomass; and, monitor resilience metrics like surface temperature, moisture levels, and wildfires will only grow in importance as humanity comes face-to-face with its most daunting self-inflicted problem to date (AI may very well be next). As we’ve shared before (c.f. Issue № 48), here at Orbital Index we’re unabashedly in support of treating climate change as the massive problem and opportunity that it is and of focusing humanity’s substantial ability to produce, problem-solve, and build on securing a livable and pleasant future—one where we can turn our focus toward the stars without ignoring existential threats at home.

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We know many of you will miss The Orbital Index (and we’ll miss you too!). As we wind things down, we plan to move the current mailing list to a new list dubbed Orbital Index: Extended Mission. We might use it occasionally for space-related thought pieces or updates if the inspiration strikes, but we’re making no promises, and there definitely won’t be a regular cadence. In the meantime, don’t hesitate to send us a note.

Please also follow us individually: Ben (LinkedIn, Twitter/X, BlueSky), Andrew (LinkedIn, Twitter/X, BlueSky) & Sarajane (LinkedIn, BlueSky)

Fortunately, if you feel the need to plug an Orbital Index-sized hole in your inbox, there are other excellent space newsletters out there. Here are some we recommend:

Jatan.space, the source of Moon Monday and Indian Space Progress – Covering all space things Lunar & Indian
China Space Monitor – Doing the hard work to unwind the ever-developing Chinese space industry
TerraWatch Space – Earth Observation industry analysis
Europe in Space – Space tech paid for with Euros (the website as well as some issues are free)
Guide to Space, Starts With A Bang, and Bad Astronomy – Papers, space science & cosmology (OTOH, if you’d rather cosmetology, we recommend thi s)
Satellite Spotlight and Payload – Investments, events & space business news
Rocket Report – Rockets!

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Thank you to all of our supporting members who made this newsletter possible: Evan Maynard, Will Deaton, Marijan Smetko, Sam Anderson, Thomas Smyth, Thomas Paine, Manuel Imboden, Galen Stevens, Samuel Trask, Bill Allen, David Rolling, Eliot Gillum, Dave Gallagher, Jesse Coffey, Lindy Elkins-Tanton, William Aaron, Brian, Frederic Jacobs, Michael Barton, John Frank, Austin Link, Ben Frank, Mike Curtis-Rouse, Matt Harbaugh, and Dan Gluesenkamp. (To those of you who opted to keep your support anonymous, thank you too!)

We also couldn’t have done it without generous corporate sponsors, listed here in order of first appearance: Spaced Ventures, Xometry, Back to Space, Formlogic, Epsilon3 (our longest sponsor at 211 issues, right up to the end; thank you!), First Resonance, Spire, A.I. Solutions, Elodin, AllSpice.io, and CSC Leasing.

Thanks for sticking with us to the very end. And so, for now… so long and thanks for all the fish!

—Andrew & Ben

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Humanity’s last view of JWST, departing to stare deep into the cosmos.

“The sky calls to us. If we do not destroy ourselves, we will one day venture to the stars.” – Carl Sagan

Fin.
❤️ 🪐 ☄️

The Quantum Cat in 2026 - The Quantum Cat

2026-01-04T13:30:30.000Z

First, I want to take the opportunity to say thank you to all of you for reading, for subscribing, and for your kind feedback.

I set out at the start of last year to write more often, while still focusing on quality over quantity. In practice, that has meant devoting more time to both researching and writing. Luckily, this has been enjoyable. As I wrote last year, it is easier to write about things I find interesting, and this year I have been fortunate to cover everything from the rusting of our Moon to the lost sisters of the Pleiades.

In the coming year I hope to keep that up, and so I also want to take this opportunity to renew my commitment to writing about interesting things, and to taking the time to make that writing good.

The Year Ahead

Aside from that, I have a few other things to announce:

My aim remains to send out about one email per week. I don’t always meet this target, so in practice it will probably be a bit less.
For the past year, paid subscribers have been getting additional articles. This comes to about one extra article each month, though again, I will try to increase this rate. Most of these articles are “deep dives”, that is, they explore a topic in greater detail. Examples from the past year include the Gaia telescope, the evidence for recent supernovae close to Earth, and the ways in which we make progress in science.
For the next week, I will offer a discount on subscriptions: $30/€25 per year, or $3/€2.50 for a month. Please do consider taking one.
That said, I am not fully happy with the subscription model Substack employs. I am currently working on re-editing and updating articles I’ve written over the past year, including those that were for paid subscribers only. My aim is to collect these in an e-book or PDF format and make this available for a one-time purchase (i.e. with no subscription necessary). Paid subscribers will get early access to the articles and free access to the booklet. If this trial works well, I plan to offer more such booklets in future for those who want to support me without signing up for a subscription.
I’d like to thank all those who have written to me over the past year to ask questions or just to give some kind words! Please don’t hesitate to get in contact with any feedback or questions. I’d be especially happy to hear about any articles you liked (or hated!), any topics you’d like to hear more or less about, or any questions you have.

Highlights from 2025

The Year in Space and Physics - The Quantum Cat

2025-12-31T13:30:40.000Z

Easily my favourite image from the James Webb Telescope this year: it shows Pismis 24, a young cluster of stars more than five thousand light years distant. Credit: NASA, ESA, CSA, and STScI, A. Pagan (STScI)

I spent some time, this summer, in the valley of the Vézère in southwestern France. People have lived there for a long time. Caves, of which there are dozens in the rocks and cliffs of this valley, show the traces of inhabitants stretching back over four hundred thousand years. In many there are ancient works of art: paintings of mammoths, of constellations, and, in a few rare cases, of humans themselves.

As I stood there, looking up at the cliffs and caves, trying to imagine the long-gone world these people lived in, another story came to my mind. In his book Wind, Sand and Stars1, Antoine Saint-Exupéry wrote of plateaux he had flown over and landed on in the Sahara Desert. These, he says, were made of hard limestone, formed from the slow accumulation of sea shells over the ages.

That, amid the dry sands of the desert, was strange enough. But having landed on them, he noticed something else. Scattered across the brilliant white surface of these plateaux were hard black pebbles. Each was heavy and cast in the shape of a tear drop. They had, he realised, fallen from the heavens: a long slow rain of rock; each plateau a sheet stretched under the stars and slowly gathering their dust.

“We are living on a wandering planet”, he notes in that book. And so we are. Things are vaster than we imagine, tied together across spans of space and time that humble our self-importance. The discoveries of science and the work of engineers cannot protect us from this; our only defense, indeed, is to look up and wonder.

Life Beyond Earth

“Year after year”, H.G. Wells wrote in 1896, “...there recurs the question as to the existence of intelligent, sentient life on the planet Mars”. Things have not changed. More than a century later we still speculate about life on Mars, though admittedly few today think that sentient beings might one day be found there.

Back then, scientists thought Mars might be rather Earth-like, with changing seasons, vegetation, and regular rainfall. Today we know it is not – Mars is a dry, dead place, one that has seen little change in the past three billion years. Yet we also know this was not always the case. Once Mars really was Earth-like, and had flowing water, seas, and a thick warm atmosphere.

This means it could also have been alive. And this year, researchers announced the discovery of a tantalising hint of this long-gone world. A rock examined by the Perseverance rover shows plausible signs of ancient biology, they said, and contains a mix of minerals that on Earth would be a sure sign of life.

For now, though, this remains speculation. The researchers called the signs a “potential biosignature”, and cautioned that a closer look would be needed to confirm their origin. That means we either need to get the rock back to Earth – for which budgets are sadly tight – or send people to Mars to look at it directly. Neither seems likely to happen any time soon.

Other researchers have focused their attention on worlds far beyond the solar system. The James Webb telescope has been studying the Trappist system, a collection of seven rocky planets a few dozen light years away. In theory some of them could have the right conditions for life.

So far, however, Webb’s data has been discouraging. Its studies of the innermost planets of the system have found them to barren worlds more akin to Mercury than Earth. Yet data from the outer planets – including those thought to be most habitable – is still to be released. Next year might, then, bring an exciting discovery of a world with a thick atmosphere and warm temperatures.

Studies are also ongoing of K2-18b , a world that shows hints of life. Its atmosphere, according to studies released last year, contains traces of dimethyl sulphide. On Earth, this gas is made by life – and so its presence on an alien world is intriguing. But other researchers again urge caution: the evidence is still weak, and even if the gas is there, we have no clear proof it is being made by living creatures.

Vera Rubin and Interstellar Comets

The second half of the year brought a rare visitor to the solar system. Comet 3I/Atlas was spotted by telescopes on July 1st, heading rapidly towards the inner planets. Astronomers soon realised it had come from interstellar space, and so this comet was distinguished as only the third object known to have visited from the stars.

Analysis showed 3I/Atlas was probably billions of years old, and likely older than the solar system itself. Although its origins remain unknown, we believe it ultimately came from a far distant and very ancient star system. At some point it was hurled out towards the stars, and it has since spent several billion years wandering the galaxy alone.

Its encounter with the solar system was a rare event for both the comet – at least a million years have passed since it last came so close to a star – and for us. Astronomers wasted no time in studying 3I/Atlas. Telescopes watched as it flew through the solar system, swung past Mars, and then passed on the other side of the Sun. It is now heading back out into interstellar space, and should once again cross the orbit of Jupiter next year.

After that, however, interstellar comets may become a more regular sight. Dozens of them are probably transiting through the solar system right now, but since most are faint and hard to see, we simply don’t spot them. The new Vera Rubin observatory in Chile will change that: it is designed to survey the whole southern sky in unprecedented detail, and will allow astronomers to find millions of objects that have so far been missed.

This bonanza of discovery may open the possibility of getting a close-up view of an interstellar comet. Europe is working on the Comet Interceptor, a spacecraft that will launch by the end of the decade and that will then wait for a suitable target to come along. An interstellar comet, ESA has said, would be a tempting object for it to examine. And with Vera Rubin, we should have plenty of options to choose from.

A New Race to the Moon?

Once again, NASA failed to land humans on the Moon.

No surprise, you might think – after all, were they really trying? But as recently as 2023, NASA’s stated goal was to return to the lunar surface by the end of 2025. Deadlines have, of course, slipped. NASA’s new goal is to reach the surface by 2027, though even this relaxed target seems hard to meet.

This much delayed schedule has raised concerns that China will get there first. Indeed, they might. In recent years China has made rapid strides in its space program. It has built a space station, tested reusable rockets, and mastered the art of landing and taking off from the surface of the Moon. It still needs a Moon rocket and a lander capable of carrying astronauts, but work on both seems to be well underway.

With all this, China hopes to put an astronaut on the lunar surface by 2030. That gives NASA some room to delay further – but fears are rising in Washington that America simply won’t make it in time. There is, acting NASA administrator Sean Duffy said this year, a new race afoot, and America needs to move faster if it wants to win.

The coming year should make the state of things clearer. NASA wants to launch Artemis II in February. That mission, if it succeeds, will carry astronauts around the Moon for the first time since the 1970s. Alongside that, SpaceX hopes to make progress with Starship, the spacecraft that the crew of Artemis III will use to descend to the surface.

If both projects go well, America has a good chance of reaching the Moon this decade. But if not, then China will look like the favourite, and the wisdom of declaring a new space race will surely be questioned.

The Shifting Balance of Science

It is not only in space that the balance of power seems to be shifting. In recent years China has invested in scientific facilities. The world’s largest single-dish radio telescope is nestled in the hills of Guizhou, one of its most advanced X-ray lasers is in Shanghai, and there is now also a powerful neutrino observatory buried under a mountain in Guangdong.

Although metrics of scientific output are hard to compare, the investment in new world-class facilities shows that China is serious about its scientific research. And it comes as a stark contrast to the current policies in the United States, which have led to sharp reductions in research funding.

This is not, to be clear, a new trend. The collapse of the famed Arecibo telescope in 2020 was preceded by cuts in its budget for maintenance. Lack of funds also ruled out the construction of any replacement observatory. American scientists have been trying to find money for two large new telescopes for years – and now, with cash still short, it seems likely that one of them will move to Europe instead.

The result of all this will not be a sudden halt to American science. Indeed, in many ways America is still the world’s scientific superpower: there is nothing else like the James Webb Space Telescope, and much of the research behind the AI revolution took place in the United States. But the balance of where scientific progress is made is shifting.

This is a matter of consequence. Physics is not just a subject of academic curiosity. It is the field from which much of the modern world has emerged: without the work of Carnot and Kelvin we would not have perfected the steam engine; without the discoveries of Maxwell we would not have mastered electricity; without the theories of Einstein we would not have built the atomic bomb.

This, very deliberately, is not a political newsletter. But whether we like it or not, science does rely on politics, and in its turn dictates the future shape of the world. The breakthroughs awaiting in the next few decades – from quantum computing to nuclear fusion – will in all probability be just as significant as those of centuries past. Basic research may not always have an obvious payoff, but history shows that civilizations which abandon it will inevitably fall behind.

The Most Popular Articles of 2025

Saint-Exupéry struggled to find the right title for this book. In the original French it is named Terre des Hommes, or Land of Men. I recommend you read it.

Issue No. 349 - The Orbital Index

2025-12-24T00:00:00.000Z

Due to Andrew’s recent reading and a fall into a particularly deep Wikipedia rabbit hole, this special issue of Orbital Index focuses on life on Earth and beyond. No issue next week. Happy New Year!

The Orbital Index

Issue No. 349 | Dec 24, 2025

🚀 🌍 🛰

¶Life shaped the Earth. Biology and geology seem to operate on dramatically different time scales, but on Earth, they are intimately linked. For example, limestone, and thus its metamorphic form, marble, is made of calcium carbonate, often from deposits accumulated by corals, mollusks, and single-celled organisms (for example, the pyramids of Egypt are made almost entirely of fossilized foraminifera). The cherts of the Bay Area are accumulations of microscopic radiolarian and diatom skeletons, sometimes with traces of the oil they once used for buoyancy. Meanwhile, life also shapes our climate and landforms, with vegetation changing erosional patterns, turning badlands into jungles, and over eons, shaping mountain ranges themselves. Cycles of global glaciation, both ancient and more recent, may be caused by the biosphere’s uptake of CO2. It’s even possible that, without life, a runaway greenhouse effect could have dried up the oceans and left Earth looking something like Venus—and without oceans enabling flux melting of subducting oceanic crust, arc volcanism may also have stopped. Biology terraformed our planet. Life may also enable planets outside of their stars’ nominal habitable zones to become habitable (paper).

Chert on Skyline Boulevard in the East Bay hills above Oakland, CA. Image credit: Andrew Alden of the excellent Oakland Geology blog (and book).

The Orbital Index is made possible through generous sponsorship by:

¶‹Sponsored› Scaling a space business often means investing heavily in equipment and technology long before revenue arrives. For nearly 40 years, CSC Leasing has helped deep-tech and space-tech teams acquire the labs, test gear, and manufacturing tools they need without burning equity on depreciating assets. Our flexible, non-dilutive financing preserves cash while adapting to the rapid, iterative cycles of frontier engineering. With a self-funded model and lease lines ranging from $100K to $50M, CSC equips innovators to build, test, and launch what’s next. Thank you, Orbital Index, for providing reliable news and updates for the last 7 years!

¶Life shapes our atmosphere. For most of Earth’s history, the sky would have been hostile to us. The Great Oxidation Event marks the moment biology (starting with microbes) pushed oxygen levels high enough to permanently alter the planet’s chemistry, creating an oxygenated atmosphere and an ozone layer that allowed aerobic life to flourish. The modern biosphere maintains this breathable atmosphere, and also releases other consequential (if sometimes strange) emissions: forests produce isoprene, a biogenic volatile organic compound, whose oxidation products can drive new particle formation in the upper troposphere (recently reproduced in CERN’s CLOUD chamber – paper), creating condensation nuclei that seed cloud formations. Carbonyl sulfide (COS/OCS) is even more interesting: sea animal colonies can shift Antarctic tundra soils from being an OCS absorber to an emitter by altering soil chemistry and microbial communities (e.g., penguins pooping and walking around on the tundra). Plants are typically a one-way absorber of OCS, making it a marker for photosynthetic carbon dioxide uptake and useful for estimating gross primary production that is more in line with other estimates than existing photosynthesis estimation methods (~120 PgC annually traditionally vs 157 ± 8.5 PgC via OCS – paper). These and other fluxes build into a non-mystical, feedback-only version of the Gaia hypothesis developed by Lynn Margulis and James Lovelock: life and environment co-evolved into coupled feedback loops that can stabilize (or destabilize) our planet’s atmospheric states (without any need to claim purpose, a point of common criticism). And, the Gaia hypothesis can be turned outward: Lovelock’s intuition is that a planet-scale biosignature is atmospheric disequilibrium: look for combinations of gases that shouldn’t persist together without a large, continuous source—in our case, life. Which brings us to the sobering present: Ben recently read Gwynne Dyer’s excellent Intervention Earth, which makes it hard to avoid the conclusion that humanity—having attained a geologic-scale atmospheric impact—may end up having to intervene more heavily in atmospheric chemistry and radiative balance than any of us would like, not because it’s appealing or elegant, but because our timeline doesn’t allow for anything less.

In this diagram, penguins jumping on land scare a sea lion and squeeze OCS out into the atmosphere… or something.

¶Life shaped our minerals. Life’s machinations also resulted in many of our minerals. It’s well known that coal, oil, and natural gas, the fuels of humanity’s rise (and maybe demise), are carbonized organic compounds built from CO₂ that was reduced by plants and algae. Less well known are the banded iron deposits from the Great Oxidation Event, which are a key source of iron for industry. These were formed when life added oxygen to our air, creating our protective ozone layer and rusting the planet (more above). This life-derived oxygen is one of the reasons Earth has 6,188 officially known minerals, while Mars has 161—a majority of our minerals may exist only due to the free oxygen made available by life. (Mars surely has more, but we won’t find them until we can stumble around and hammer on rocks.) Also likely due to life: a large amount of our native sulfur (although we’ve seen some on Mars); bog iron ore (one of the first sources of iron for tool making) which is often concentrated by iron-oxidizing bacteria; abelsonite, a chlorophyll-like mineral likely derived from the breakdown of ancient vegetation; and, even the bioaccumulation and formation of uranium, phosphate, vanadium and gold deposits—“bacteria and archaea are involved in every step of the biogeochemical cycle of gold, from the formation of primary mineralization in hydrothermal and deep subsurface systems to its solubilization, dispersion and re-concentration as secondary gold under surface conditions.” Related: About 4% of minerals are now the direct result of human activity—known as anthropocene minerals, these occur in places like mine walls, shipwrecks, and ancient slag (paper). Andrew recently thoroughly enjoyed reading The Story of Earth by Robert M. Hazen, the author of that anthropocene minerals paper and an explorer of mineral evolution. Recommended!

Bluebell tunicates contain vanadium as vanabin. Concentrations of vanadium in some sea squirts can be 10,000,000x higher than in the surrounding seawater. It is possible that similar biological processes may have formed some vanadium ores.

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¶News in brief. Jared Isaacman was finally confirmed as NASA’s 15th administrator—here’s to hoping there’s a reasonable chunk of NASA left for him to administer ● Trump signed the ‘Ensuring American Space Superiority’ executive order which effectively ends the National Space Council (consolidating under the White House Office of Science and Technology Policy) and puts ambitious dates on numerous goals: an American Moon landing (2028), the starts of a lunar base including a nuclear surface reactor (2030), a “Golden Dome” test (2028), a pathway for commercial ISS replacement by 2030, and more ● HawkEye 360 raised a $150M Series C ● Starfighters Space went public, raising $40M to accelerate development of their supersonic aircraft capable of sub-orbital launches ● Innospace (c.f. Issue 342) attempted the first orbital launch from Brazil this week (and the first private South Korean orbital launch attempt), but their Hanbit rocket failed roughly one minute into flight ● Indian startup Digantara closed $50M Series B to use their situational awareness satellites for missile defense ● EraDrive raised a $5.3M Seed to scale the production of its self-driving modules that allow satellites to maneuver autonomously ● Tony Bruno, the president and CEO of ULA, stepped down from his role after 12 years—we’ll miss his fun, positive, and candid play-by-play of the industry and ULA’s part in it ● Despite Roscosmos anticipating fixes by the end of February 2026, NASA has bumped up Dragon ISS resupply missions due to the recent Soyuz launch pad incident in Baikonur ● Rocket Lab executed its first dedicated launch for JAXA aboard Electron, which is now at a record 19 launches on the year for the mature vehicle ● Startup Max Space unveiled plans for a commercial space station, with a single module that can launch on a Falcon 9 and expand to 350 cubic meters once in orbit ● Japan’s new-ish H3 rocket suffered an anomaly in the upper stage, failing to place a navigation satellite in a high enough orbit ● SpaceX confirmed IPO prep for 2026 ● One of NASA’s ESCAPADE spacecraft experienced lower-than-expected thrust during a burn, delaying its trajectory correction maneuver ● As NASA’s MAVEN spacecraft remains unresponsive and likely unstable, another Mars circling spacecraft (the Mars Reconnaissance Orbiter) continues to operate nominally, recently capturing its 100,000th surface image using the HiRISE camera.

A view of the region called Syrtis Major, created by a massive shield volcano, is shown in MRO’s 100,000th image from its HiRISE camera. Credit: NASA

¶Etc.

A recent study shows that even the Earth’s lower mantle has been affected by life, finding that diamond-bearing volcanic kimberlites from deep within the mantle exhibit a different carbon signature if they formed after the rapid development of fauna in the Cambrian Explosion. This is because seafloor sediments containing biological matter were subducted at plate boundaries and ended up deep in the mantle in kimberlites.
There's a 'Subterranean Galapagos' deep inside the Earth, and studying 1.6 billion-year-old water from a Canadian mine.
CERN provides free instructions on how to build a cloud chamber at home.
Blue Origin’s latest New Shepard flight included ESA aerospace and mechatronics engineer Michaela Benthaus, who is likely the first wheelchair user to cross the Kármán line.
Interstellar comet 3I/ATLAS made its closest approach to Earth on Dec 19th, roughly 270 million kilometers away.
Jatan Mehta shared a year-end “Achievements and shortfalls in global lunar exploration in 2025.”
Katalyst Space selected Northrop Grumman’s Pegasus XL air-launched rocket (last flown in 2021) to deliver its robotic spacecraft to orbit for its NASA mission to boost Swift’s orbit, which is currently at too low of an inclination for most small rockets to reach from their designated launch sites.
The stuff of nightmares: a 10 million solar mass black hole moving at 1,000 km/s (paper). This is the first confirmed runaway supermassive black hole, and it is pushing a massive bow shock in front of it while dragging a 200,000 light-year-long tail behind. Supermassive black holes moving at 0.003 c might be hazardous to your health.
Plate tectonics, meanwhile, may increase the probability of life by “forming geological structures such as mountains, volcanoes and oceans, which also allow moderate weather and climate patterns to develop. Through weathering, nutrients are released into oceans. By creating and destroying habitats, plate tectonics puts moderate but incessant environmental stress on species to evolve and adapt.” The probable rarity of plate tectonics in the galaxy is even proposed as an addition to the Drake equation (paper). Our own planet’s plate tectonics may have been jump-started by impacts, with chemical traces in zircon crystals aligning with the period when “our Solar System passed through the galaxy’s spiral arms, which are densely packed with stars and gas. In these crowded regions, extra gravitational forces may have disturbed icy comets at the edge of our Solar System, knocking some onto paths that sent them crashing into Earth.” Time for the field of paleoastrobiogeology!

Plumes of water spewing from Saturn’s icy moon Enceladus show signs of even more molecules useful for life: aromatics like benzene, oxygen compounds, and esters and alkenes, including molecules which play a role in amino acid chemistry, all consistent with the presence of hydrothermal activity. This new data comes from the re-analysis of an old Cassini flyby in 2008, when the spacecraft, moving at ~18 km/s, collided with and ionized water vapor from the plumes, revealing signatures of its component molecules (paper). XKCD #2359, below, seems apropos.

The Week in Space and Physics: Shades of Dark Matter - The Quantum Cat

2025-12-17T13:30:47.000Z

The Red Spider Nebula, imaged by the James Webb Space Telescope. Credit: ESA/Webb, NASA & CSA, J. H. Kastner (Rochester Institute of Technology)

Two short notes this week:

I have recommended Dr Larry Krumenaker’s excellent newsletter on astronomy to many of you before. He is now (re-)launching The Classroom Astronomer, a newsletter focused on astronomy education and resources for all levels. If you are interested in learning more about the practical art of astronomy, it is well worth checking out.
In the past few weeks I have been working on collecting and re-editing several of my best articles from the past two years. As a trial of an alternative to paid subscriptions, I plan to soon offer this collection in a digital magazine/booklet format. Current paid subscribers will get it for free, for everyone else it will be available at a reasonable price. More information to follow in the coming weeks!

For almost a century, we have known galaxies do not move as they should. Something else seems to be out there. Something invisible to our eyes, yet something that exerts an irresistible pull on the matter we can see, and that therefore accounts for this mysterious motion.

We call this dark matter, and calculations show that there must be a lot of it. Indeed, if we are to account for the way galaxies spin and move, we must add about ten times more matter than we can see – and that implies the visible universe is only a small fraction of the total. The problem, of course, is that we have no idea about the true nature of this dark substance.

Most researchers reckon it must be made of some unknown class of particles, ones that can exert a gravitational pull but emit little in the way of light or any other kind of radiation. Yet, under some models of dark matter, its presence might be betrayed by a faint signal of gamma-rays. Though the particles themselves do not give out this radiation, they are expected to interact through the weak nuclear force. If they do this, the particles can occasionally collide, convert into other particles, and release gamma-rays in the process.

This signal is expected to be very weak. But if it is there, it will show up around the edges of galaxies, where dark matter is thought to cluster in large halos. Efforts to find it have thus focused on surveying nearby galaxies with gamma-ray telescopes. Until now, however, little solid evidence has emerged to suggest it really exists.

In November, however, Tomonori Totani, an astronomer at the University of Tokyo, claimed to have found it. He examined fifteen years of observations of our galaxy taken by the Fermi Telescope, an orbiting gamma-ray observatory. After accounting for every possible source of gamma rays – from cosmic rays to vast bubbles of gas – he found a slight signature remained.

The signal looks similar in shape to the expected dark matter halo around the galaxy. It also matches some predictions of how this dark matter particle might act. According to Totani, this is a huge breakthrough: it is, he said, “a major development in astronomy and physics”.

Yet, there is reason to be sceptical. For one thing, there are other unexplained gamma-ray signals out there, including one shining in the heart of our galaxy. These might be coming from dark matter, but they might also be coming from some other unexpected source. Just because we see a signal, sadly, does not mean we know what is causing it.

The End of the Sterile Neutrino?

There is, of course, no shortage of other ideas about what dark matter might be. Some physicists think it could instead be made of a particle called the “sterile neutrino”, a fleeting and almost invisible particle that would interact only through gravity.

In theory, the idea is attractive. Neutrinos are already mysterious and hard to detect. They emit no light, and interact with other kinds of matter only through the weak nuclear force. In practice, that means they barely interact at all: a neutrino can pass through an entire planet without ever actually colliding with or being deflected by another particle.

The sterile neutrino, however, would escape the pull of the weak force as well. That would make it essentially impossible to detect. As neutrinos have almost no mass, even their gravitational pull would only be significant in large numbers – as if, for example, they clustered in enormous halos around the edges of galaxies. Naturally, then, we have no current proof that they exist at all.

But there are known gaps in our understanding of neutrinos. For one thing, even though standard theories suggest they should be massless, like the photon, experiments suggest they do in fact have a very small, but non-zero, mass. The sterile neutrino might, therefore, emerge from the cracks in our current theory, and thus turn out to exist after all.

Fortunately, there are experiments we can do to try spotting their subtle influence. Two of these have been running for the past few years in Germany and the United States. KATRIN, running in Germany, has made careful measurements of the electron neutrino, one of the three known varieties of the neutrino. If the sterile neutrino exists, it should create a slight change in the properties of this particle – something that KATRIN can spot.

The other, MicroBooNE at Fermilab, is looking at how muon neutrinos transform into electron neutrinos. Again, the sterile neutrino should influence the details of this transformation, and so this experiment could also hint at their presence.

Sadly, however, new results from both experiments have shown no signs of the particle. That doesn’t mean the particle can’t exist, but it does undermine many of the theoretical reasons for believing it might.

But then again, neutrinos are nothing if not surprising. More neutrino experiments and observatories are being built across the world. One of them, given enough time, may still end up revealing the closely guarded secrets of dark matter.

Lightning on Mars

When Mariner 9 approached Mars in 1971, researchers were dismayed to find the entire planet shrouded in dust. Winds blowing down a long valley had swept up clouds of dust from the slopes of Hellas, and this had spiralled into a storm of global proportions. By the time Mariner arrived, the surface of Mars – from deepest valleys to highest peaks – was obscured by a cloud of dust forty miles deep.

Such things are a constant danger on Mars. Global storms erupt once every few years, and then take months to abate. Smaller ones happen all the time, and have been observed on many occasions by probes and orbiters. But now, for the first time, researchers have found signs they produce thunder and lightning.

The discovery came from the Perseverance Rover. Microphones on board picked up clapping sounds as dust storms passed near the rover. At first, researchers thought this was explained by grains of dust hitting the microphones. But a follow-up found they were linked to small bursts of electromagnetic energy – and this could only be explained if small sparks of electricity were crackling in the Martian atmosphere.

This is probably caused by electrical charge building up as dust particles dance and collide in storms. This happens on Earth too – most visibly in the ash clouds thrown out by volcanoes – but since our atmosphere is thicker, far more charge needs to be present to cause lightning. On Mars, with its thinner air, even small dust devils can spark thunder and lightning.

Farewell to MAVEN

NASA lost contact with MAVEN, a spacecraft that has been in orbit around Mars for more than a decade. According to operators, MAVEN was functioning normally on its final contact. However, the spacecraft then passed behind Mars, and did not re-establish communication upon its return.

MAVEN’s scientific instruments have helped researchers study the atmosphere of Mars and how it interacts with the solar wind. But the probe also acted as a radio relay, transmitting signals between the rovers on the surface of the planet and operators back on Earth.

There are a handful of other relays operating around Mars, but the loss of MAVEN will cut overall communications capacity. Few new relay satellites are planned – and with the Trump administration seeking to cut the budget available for such missions, the prospects for a new one any time soon are poor. Barring a miraculous revival of MAVEN, this looks like a sad loss to our efforts to explore the red planet.

Issue No. 348 - The Orbital Index

2025-12-17T00:00:00.000Z

The Orbital Index

Issue No. 348 | Dec 17, 2025

🚀 🌍 🛰

¶Papers

ESO’s VLT observed a rogue planet—a free-floating planet unbound to any star—rapidly accreting material (paper). This observation suggests that some rogue planets may form through accretion, like stars, rather than forming in a stellar system and then escaping.
Observations in 2023 show rings of debris forming around the small, 200 km solar system body Chiron, which orbits between Saturn and Uranus. If accurate, this would be the first time we’ve watched rings form (paper).
Pulsars typically stop pulsing under a certain rate of rotation. However, some pulsars have been observed to be active even below this expected limit. The culprit might be tiny mountains, just centimeters tall, which would amplify local electric fields and enable lower-energy emissions (paper). The researchers also propose that for this to be true, neutron stars might be made of "strangeon matter," an “exotic form of matter bound together by the strong nuclear force rather than electromagnetic forces. This material would be tough enough to maintain surface features against the neutron star's extreme environment, with binding energies millions of times stronger than ordinary matter.”
A pair of white dwarfs, 150 light-years away, are slowly spiraling toward each other (with energy radiated as gravitational waves). The duo has a combined mass of 1.56 Suns, making them the heaviest Type Ia supernova progenitor system identified, well over the 1.4 solar-mass Chandrasekhar limit (paper). When they eventually make contact and go supernova, they’ll be ten times brighter than the full Moon when viewed from Earth. On the other hand, it’s unlikely Earth will exist in ~23 billion years when this happens.
A black hole 10 billion light-years away probably consumed a massive star in a tidal disruption event and emitted a flare 30x brighter than any previously observed from a black hole (paper). At its peak, it shone with the light of 10 trillion suns. Sounds a bit poetic, don’t it?

“We haven't actually seen a star fall in since we invented telescopes, but I have a list of ones I'm really hoping are next.” XKCD #3072

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¶High-flying filling stations, off-planet petrol, & the future of fuel. Since the beginning of the Space Age, orbital refueling has remained an unfulfilled dream that promises to revolutionize the space industry—primarily by extending the life and range of spacecraft. Refueling would enable greater mass dedicated to payload at launch, more complex in-space assembly, access to new and more plentiful target destinations, and more reusable space tugs. Liquid methane (LCH4) boils at -162 °C, oxygen (LOx) at -183 °C, and hydrogen (LH) at -253 °C, while other common liquids freeze in space, including RP-1 (-51 °C), hydrogen peroxide (−0.89 °C), water (0 °C), and hydrazine (2 °C). Storing these propellants in space, therefore, requires advanced thermal management to prevent boil-off or freezing using tank geometry, materials and insulation, active cryocoolers/heaters, sun shades, and other thermal control systems. Challenges also include microgravity effects on propellant (difficult liquid mass gauging and unpredictable liquid/gas distribution), increased operational complexity due to rendezvous, proximity operations, and docking (RPOD) for transfers, propellant depot orbital accessibility, hydrogen embrittlement of storage tanks, and the need to periodically refill depots. But technology is slowly inching toward refueling. Starting in March 2007, DARPA’s Orbital Express mission performed multiple hydrazine fuel transfers between the prototype servicing satellite (ASTRO) and a surrogate satellite (NextSat), and NASA’s Robotic Refueling Mission (RRM) included three phases of cryogenic fuel transfer work on the ISS in the 2010s. Orbit Fab’s Tanker-001 Tenzing launched to a sun-synchronous orbit (SSO) in 2021, carrying high-test hydrogen peroxide (HTP) to test the Rapidly Attachable Fluid Transfer Interface (RAFTI) fueling port. SpaceX’s Starship Flight 3 in March 2024 tested refueling technologies by transferring 5+ metric tons of cryogenic LOx from one internal tank to another. Earlier this year, the Chinese Shijian-25 demonstration refueling satellite docked with Shijian-21 and potentially transferred propellant. Upcoming missions include NASA’s LOXSAT (NET early 2026), which will demo a cryogenic fluid management system. Orbit Fab plans to deliver up to 1,000 kg of xenon gas to power the ion thrusters of Astroscale’s Life-Extension In-Orbit (LEXI) geostationary servicing satellite (NET 2026), and up to 50 kg of hydrazine to one of the two Tetra-5 satellites operated by the U.S. Space Force (both via an integrated RAFTI port). Astroscale’s Prototype Servicer for Refueling (APS-R) will attempt to refuel the other Tetra-5 satellite in mid-2026, while Northrop Grumman’s Passive Refueling Module (PRM) will refuel Tetra-6 in 2027. Of course, the ultimate goal—one that would drastically reduce launch cost on Earth—would be to have all stages of propellant production (mining, processing, and storage) performed in space to avoid hauling liquids out of Earth’s deep gravity well

A 1971 concept of an orbital propellant depot. Credit: NASA’s Marshall Space Flight Center.

¶CINEMA and CMEx move forward. Cross-scale Investigation of Earth’s Magnetotail and Aurora (CINEMA) is a small-class explorer mission focused on improving our understanding of magnetic convection in Earth’s magnetotail, which drives energetic, sometimes explosive, plasma flows associated with aurorae and fast plasma jets. The mission will now move into Phase B development, planning the flight system and mission operations. If selected for full development, with a total mission cost not to exceed $182.8M (excluding launch), CINEMA would launch nine formation-flying small satellites into three planes in polar orbit, each carrying an identical instrument set including an energetic particle detector, an auroral imager, and a magnetometer. Meanwhile, CMEx (Chromospheric Magnetism Explorer) was selected for an extended Phase A study (12 months; $2M). CMEx is a proposed single-spacecraft concept that builds on proven UV spectropolarimetric instrumentation demonstrated on NASA’s CLASP sounding rocket flights, and would observe the Sun’s inner chromosphere to understand the origins of solar eruptions and identify the magnetic sources of the solar wind, supporting improved space-weather prediction relevant to satellite and astronaut safety.

If fully developed, Cinema’s nine cubesats will fly on three orbital planes, creating a grid of identical sensors to measure Earth’s magnetotail.

‹Support Us› Orbital Index is made possible by readers like you. If you appreciate our writing, please support us with a monthly membership!

¶News in brief. All eight docking ports on the ISS were occupied simultaneously for the very first time—spacecraft included both cargo and crew variants of Dragon, two Soyuz and two Progress vehicles, Japan’s HTV-X1, and a Cygnus XL ● NASA lost contact with MAVEN, a spacecraft that's been circling Mars since 2014 ● Two Chinese taikonauts conducted a spacewalk to inspect the damaged window on the Shenzhou-20 and install additional debris protection on Tiangong ● China and Brazil began building a joint space astronomical laboratory, despite US pressure in Latin America to minimize ties to China ● AnySignal raised a $24M Series A to ramp up their radio manufacturing operations ● K2 Space raised a massive $250M Series C to continue building high-power satellite buses ● SpaceX reused a Falcon 9 booster for the 32nd time, a new record—Falcon 9 has now more than 3x’d its original reuse goal of 10 flights ● British startup Odin Space raised a $3M seed round to develop sensors that allow spacecraft to detect sub-centimeter orbital debris ● California-based Fortastra raised $8M in seed investment to develop orbital defense satellites ● NASA astronaut Jonny Kim and two Russian cosmonauts returned to Earth aboard a Soyuz M-27 after an eight-month stint on the ISS.

Russia’s Soyuz MS-27 capsule landing in a remote area near Zhezkazgan, Kazakhstan, bringing one NASA astronaut and two Russian cosmonauts back to Earth after an eight-month stint at the ISS

¶Etc.

This Proton M rocket explosion from 2013 (slow motion HD video) is WAY too much like the rockets Andrew used to build in KSP. Related: things KSP teaches you that are wrong.
Do datacenters in space make economic sense? A long-form, delightfully interactive, deep dive from Andrew McCalip.
If you made a beach out of sand grains proportionate in size and quantity to the stars in the Milky Way, what would that beach look like?
A look at Skylab’s final orbit and reentry in 1979, including a pieced-together audio track of the final telemetry and NASA commentary during tracking.
The Space Freighter and Star-Raker single-stage-to-orbit space plane, envisioned in the 1970s for delivering massive components to space for space solar energy and other missions.
Impulse and Starfish quietly conducted an RPO(D) experiment over the past several months (minus the D), using Starfish’s software and Impulse’s Mira spacecraft to bring it within 1,250 km of an older Mira vehicle. The Impulse vehicle, using high-thrust chemical propellants, was not heavily modified to enable this mission, other than the addition of a single camera and Starfish’s flight computer. The mission was named Remora after the fish that attaches to a host.

Mira as seen from (a newer) Mira. Starfish took pictures during the approach of the unsuspecting older sibling to Impulse’s latest space tug.

Issue No. 347 - The Orbital Index

2025-12-10T00:00:00.000Z

The Orbital Index

Issue No. 347 | Dec 10, 2025

🚀 🌍 🛰

¶Overview Energy launches. A huge disclaimer upfront: this is the space solar energy company that Andrew co-founded and spent the last four years working on, so we cannot in any way be impartial. We do think it is very cool, though. Overview Energy came out of stealth today and announced successful power transmission from a moving aircraft to a ground receiver 5 km below, what we believe is a world first (video). Overview’s mission is to allow existing solar projects to produce power at dawn, dusk, and night, times when clean baseload power is needed but the Sun is weak or unavailable. The company’s vision is to build many geosynchronous satellites, illuminated by the Sun almost 24/7, that transmit power to large existing solar farms on the ground via a wide (~2-5 km across), invisible (near-infrared), and safe (eye safe and less than solar intensity) beam of light. This optical power delivery approach means that no specialized ground receivers need to be built, and the satellites can be a size that is manufacturable and deployable (albeit still very large) with no robotics or in-space assembly. This compares favorably to microwave space solar energy proposals, which require apertures in space that are on the order of a kilometer or more across and which may struggle with safety on the ground. Overview Energy’s next major milestone is a LEO test mission scheduled for early 2028. Overview is hiring!

In this sped-up footage, Overview Energy’s near-infrared laser successfully tracks a solar test installation from a plane circling 5 km above, delivering power to the ground. The spot is invisible to the naked eye, but shows up on a night vision camera. A very tired team rejoices. 🥂

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¶IM-3. After two almost-landings on the Moon, Intuitive Machine is steadily working on IM-3 (with fixes to its laser altimeter and crater recognition systems). IM-3 is scheduled to launch in the second half of 2026 and is contracted to deliver payloads for NASA, ESA, KASI, and others. It will land in the Reiner Gamma region of the Moon, which contains a lunar swirl, probably caused by unusual local magnetic fields. One interesting payload is JPL’s trio of four-wheeled, solar-powered, carry-on-bag-size CADRE rovers, which will work together autonomously to map an area of the lunar surface and subsurface in 3D with cameras and ground-penetrating radar. They are designed to function for one lunar day (14 Earth days)—presumably, they lack radioisotope heaters to survive the lunar night. CADRE (Cooperative Autonomous Distributed Robotic Exploration) is a step toward autonomous operation (something we discussed in Issue № 229) and multi-robot mission design—the robots form a mesh network and collaborate to map and act as distributed receivers for each other’s radar signals. At the same time, IM-3 relays their comms to Earth. Also onboard IM-3 are ESA’s MoonLIGHT Pointing Actuator retroreflector (paper) for ranging and KASI’s Lunar Space Environment Monitor, which will measure the energy distributions of charged particles on the Reiner Gamma to help understand the formation of lunar swirls and space weathering (paper).

IM-2, on its side on the Moon in March 2025, suffering a fate that hopefully doesn’t befall IM-3.

¶Astrophysics, but cold. There are nearly 70 research stations across the 14.2 million km² continent of Antarctica. Antarctica’s high altitude and dry, stable atmosphere provide exceptional conditions for astronomy by helping to minimize atmospheric distortion and reduce infrared sky emissions. Antarctica also experiences very little light pollution, low seismic activity, a six-month polar night, and the presence of circumpolar stars and constellations, which never dip below the horizon, allowing for continuous observation of those targets. A site named Ridge A, ~1,000 km from the South Pole, has been declared the best place on Earth for astronomy. One instrument on Ridge A is the remote-controlled High Elevation Antarctic Terahertz far-infrared telescope, which has been operating since 2012 for submillimeter- and terahertz-wavelength observations. Antarctica’s Amundsen-Scott South Pole Station experiences average temperatures of -49 °C, and is home to four astronomical projects: the South Pole Telescope, the IceCube Neutrino Observatory (the clear Antarctic ice enables the detection of high-energy neutrino interactions), and the BICEP3/BICEP Array. The Long Duration Balloon Facility at Antarctica’s McMurdo Station conducts scientific balloon experiments, launching payloads into the stratosphere for periods of 10-20 days to study the Earth's atmosphere and space. The Chinese Kunlun Station, located just 7.3 km from Dome A (Argus)—the highest point of the Antarctic plateau—hosts three astronomical instruments: the China Star Small Telescope Array with four 14.5-cm telescopes, the Antarctic Survey Telescope (AST3-1 and AST3-2) consisting of three 50-cm instruments, and the near-infrared telescope, which is part of the Kunlun Dark Universe Survey Telescope project. China’s Three Gorges Antarctic Eye, a 3.2-metre radio/millimeter-wave telescope, recently began observations at China’s Zhongshan Station, located near Russia’s Progress II Station and Romania’s Law-Racoviță-Negoiță Station. Some future Antarctic astronomy missions include the Dome A Terahertz Explorer-5, planned for installation at Kunlun; the Polar Large Telescope, to be built at the French-Italian station on the Dome C (Concordia) site; and the Antarctic TianMu Time-domain Astronomical Observation Array at Zhongshan. (Related: lest we forget, Antarctica is also the richest source of meteorites on our planet. Rocks seem to have trouble hiding on ice sheets.) 🔭🐧

The South Pole Telescope underneath aurora australis during the six-month Antarctic night.

‹Support Us› Orbital Index is made possible by readers like you. If you appreciate our writing, please support us with a monthly membership!

¶News in brief. NASA completed assembly of the Nancy Grace Roman Space Telescope, which may launch as early as summer 2026 ● SpaceX received environmental approval to begin building a launch site in Cape Canaveral Space Force Base for Starship Super Heavy launch and landing operations (in addition to their Starship launch tower at Kennedy Space Center) ● Reditus Space, an Atlanta-based startup, raised a $7.1M seed round to develop a reusable reentry vehicle for microgravity research ● Apparently, OpenAI CEO Sam Altman almost invested in Stoke Space amidst exploration into building a SpaceX competitor ● European countries (primarily UK, Spain, France, and Germany) committed over €900B (~$1.05T) to the European Launcher Challenge that funds commercial rocket development ● ICEYE raised a $174.6M Series E to continue scaling their SAR satellites and intelligence services ● NASA delayed an Artemis II dress rehearsal due to a ‘blemish’ on the crew module’s thermal barrier that prevented hatch closure ● SpaceX is privately offering shares at an $800B valuation, and could IPO next year ● Israeli startup Moonshot Space emerged with $12M to develop an electromagnetic ground-based launch system ● Roscosmos replaced the cosmonaut assigned to the next ISS crew mission due to alleged ITAR violations: taking images of SpaceX hardware and documentation during Crew Dragon training ● Chinese commercial rocket builder LandSpace successfully launched its first Zhuque-3 rocket to orbit (capable of 8 tons to LEO when recovered), and the booster came relatively close to sticking the landing, suffering an anomaly late in the flight during the landing burn—this is still an impressive first booster landing attempt, and illustrates how close China’s space industry is to reuse (re-entry video).

LandSpace’s Zhuque-3 rocket lifting off from the Jiuquan Satellite Launch Center in northwestern China. Credit: LandSpace

¶Etc.

A big list of cool astronomy simulations and visualizations.
That time the CIA stole a Soviet lunar probe for a night so that they could photograph it and figure out which factories had made the parts. (They actually did it twice.)
Galactic Algorithms are ones with “world-beating theoretical (asymptotic) performance,” but which are never used in practice due to complexity or incredibly high constant terms, which means that they’re only useful for data sets larger than we’ll ever encounter on Earth. For example, there is a known method of multiplying two numbers in O(n log n) bit operations, but it has a huge constant in front and requires something like a 1,729-dimensional Fourier transform. This is compared to the widely used Karatsuba algorithm for multiplying numbers in O(n^1.58) time.
The Tragic Tale Of How NASA's X-34 Space Planes Ended Up Rotting In Someone's Backyard.

This iconic photo is of Bruce McCandless, the first astronaut to fly untethered in space. His work as part of the team developing the now-retired MMU (Manned Maneuvering Unit) gave humanity its first, and only, access to solo free flight in space (MMU’s descendant, SAFER, is an emergency system and designed for emergency astronaut retrieval, not free flight). If you’d like, you can read the MMU user guide here.

Issue No. 346 - The Orbital Index

2025-12-03T00:00:00.000Z

The Orbital Index

Issue No. 346 | Dec 3, 2025

🚀 🌍 🛰

¶The ‘world’s only commercial spaceplane’ is finally sort of nearing launch. Sierra Space’s perennially delayed Dream Chaser Cargo System (DCCS) is now scheduled to launch in Q4 of next year on a Vulcan rocket, no longer planning to visit the ISS, but still attempting a runway landing at Vandenberg Space Force Base (animated launch video). The vehicle recently completed pre-flight tests at Kennedy Space Center, where it will launch. If successful, it’s not entirely clear what would be next for the reusable, autonomous spaceplane. The cargo variant of the vehicle was originally planned to start a multi-mission NASA Commercial Resupply Services-2 (CRS-2) contract for ISS cargo delivery, but that contract now seems to be in flux. Much like Cargo Dragon with its expendable trunk, DCCS includes the Shooting Star cargo module with docking hardware and solar panels for power, which will burn up on re-entry. DCCS would be capable of delivering 5 tons of cargo to the ISS, and carrying about a ton back to Earth for landing on a commercial runway while subjecting it to no more than 1.5 g. The vehicle maneuvers in orbit with ‘green’ hydrogen peroxide propellant and has folding wings that allow it to fit in standard 5-meter fairings. A crewed version (originally funded through phases of NASA’s Commercial Crew Program but ultimately passed over in favor of Starliner and Crew Dragon) could carry up to seven people to LEO, should the vehicle ever be developed (its most likely use may be commercial station deliveries in either configuration, given its partnership in the Orbital Reef, should that station ever progress).

Dream Chaser at Edwards Air Force Base, California. Credit: NASA

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¶Papers

A new paper calls into question the accelerating expansion of the Universe, potentially resolving the Hubble tension. The team produced evidence that type Ia supernovae, a key standard candle used to estimate distances in the Universe, are strongly affected by the age of their progenitor stars, with supernovae from younger stars appearing fainter than those from older stars. This fits recent data from DESI, derived from baryonic acoustic oscillations and the CMB. “Our study shows that the universe has already entered a phase of decelerated expansion at the present epoch and that dark energy evolves with time much more rapidly than previously thought.” Further updates and confirmations will be needed over the next few years (with some likely coming from Rubin LSST data), but this may be an exciting development in cosmology!
Astronomers found a Jupiter-sized planet, tidally locked to a millisecond pulsar, with an atmosphere made up of almost exclusively carbon (paper). The planet may once have been a star, but so much material has either been stolen by the pulsar or blasted away by gamma rays that what is left is Jupiter-sized. The source of the planet’s carbon-rich atmosphere isn’t yet understood. This type of system, where a pulsar consumes or ablates a planet, is sometimes called a black widow pulsar.
One long-standing, though generally poorly accepted, theory for the cause of a period of abrupt cooling of the climate 12,000 years ago—which saw the disappearance of megafauna and the Clovis culture—is known as the Younger Dryas Impact Hypothesis (YDIH). The theory posits that a comet airburst caused massive fires and subsequent global cooling, wiping out woolly mammoths and causing the collapse of the Clovis culture. No craters have been found, but a layer of black strata, which might be burnt material, as well as microspherules and platinum, has been cited as evidence. Now, a recent paper reports the discovery of shocked quartz at three well-known Clovis sites, strengthening evidence for an extraterrestrial cause. Shocked quartz—quartz sand grains with molten silica solidified in fractures—is known to occur after nuclear weapons tests and inside impact craters (the latter seeming more likely here).

“The bottom ones are also potentially bad news for any other planets in our solar system that have been counting on Earth having a stable orbit.” XKCD #3049

¶A Bigger, Newer Glenn. Following its very successful second launch, including a successful booster return, Blue Origin released an update on what’s next for its heavy lift rocket. First up are engine upgrades, with both the BE-4 and BE-3U getting thrust increases that will yield better performance for the current rocket configuration. These upgrades include subcooling for the rocket’s propellant (which SpaceX also introduced in the Falcon 9 block 5 upgrade) and will deliver ~15% more thrust to the first stage and 25% more to the upper stage (interestingly, BE-3U has only delivered up to ~70% of its current thrust capability on the test stand to date). In addition to engine upgrades, Blue will introduce a recoverable/reusable fairing on the current rocket, which should help increase launch cadence. Looking further into the future, the company intends to introduce an even larger version of New Glenn; this variant would feature 9 BE-4s and 4 BE-3Us (Blue refers to this as a 9x4 configuration, compared to the current 7x2 version). This new variant should be capable of delivering 70 tons to LEO and will require stretched tanks and a new aft thrust section. 9x4 will feature an even larger 8.7-meter fairing—altogether, this version will be taller than the Saturn V and squarely move the rocket into the Super Heavy camp (Starship will still be taller and produce significantly more thrust, however). No word on when it is planned for launch (we’d be a bit surprised to see it before 2028).

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¶News in brief. China’s uncrewed Shenzhou-22 spacecraft docked at Tiangong to reestablish a lifeboat for the Shenzhou-21 astronauts after the debris incident on Shenzhou-20 ● NASA confirmed that Starliner’s next mission in April will be cargo-only (to demonstrate the safety of the propulsion system) and reduced its number of operational missions from six to three before the ISS is retired ● Redwire won a $44M DARPA contract for a VLEO demo ● Canada is ramping its ESA contribution to $528.5M—10x its prior investment—likely a sign of strengthening ties after U.S. tariffs, helping ESA reach a budget close to its requested amount and a 17% inflation-adjusted increase over their previous ministerial in 2022 ● SpaceX’s newest Starship booster (the first for V3) burst open during pressure testing, potentially delaying the launch of Flight 12, although the company states that it still intends to launch in Q1 ● IonQ will acquire optical communications company Skyloom Global ● LeanSpace raised an $11.6M Series A to expand their software-defined satellite operations platforms ● Amazon Leo debuted a new gigabit-speed antenna for their broadband service ● German startup Dcubed unveiled three upcoming demo missions for in-space solar array manufacturing ● Quindar raised an $18M Series A to scale their mission control systems ● York Space wants to IPO ● French rocket builder HyPrSpace secured a $24.35M Series A to continue developing their hybrid rocket engines ● Agnikul Cosmos raised $16.8M to develop single-piece 3D-printed rocket engines ● Ursa Major closed a $100M Series E to scale manufacturing capabilities for their hypersonic, in-space propulsion ● South Korea successfully launched its fourth Nuri rocket, placing 13 satellites into LEO ● SpaceX launched 140 payloads (including EO satellites, OTVs, & reentry vehicles) to SSO on Transporter 15 ● A Russian Soyuz delivered two Russian cosmonauts and one American astronaut to the ISS, but unfortunately the launch pad in Baikonur suffered damage during launch (that some sources are estimating could take two years to fix), meaning Russia has lost the ability to launch humans into space, something that has not happened since 1961.

¶Etc.

NASA shared more images of interstellar comet 3I/ATLAS taken from spacecraft all over the solar system.
Moss spores survived for 9 months outside the International Space Station.
Airbus update on A320 Family precautionary fleet action (SEUs in aircraft!)
ESCAPADE, recently launched on New Glenn’s second flight, has seen first light.
All about Apollo 11’s feared biological back contamination risk and the isolation procedures applied to returning astronauts. “This is how a completely abstract argument about alien germs was taken seriously and mitigated at great effort and expense during the 1969 Apollo landing.”
ESA announced a project to study food production in space using hydrogen-oxidizing bacteria to make protein from microbes that need only air, hydrogen (via electrolysis), and a bit of astronaut urine (for urea). Think Soylent for astronauts. (An interesting effort to find the most efficient possible path to generate food in space, or for an emergency on Earth, is ALLFED. Here’s a review paper of non-agricultural food production, including wood/biomass to sugars, single-cell proteins from various gas/liquid feedstocks, including hydrogen, chemical synthesis from hydrocarbons or CO₂, and precision fermentation. And here is another on direct chemical synthesis of food.)

140 payloads vertically stacked in the payload fairing of the Falcon 9 for SpaceX’s Transporter-15.

Notes On Learning Hard Things - The Quantum Cat

2025-12-01T13:32:25.000Z

The number one most read page on my site is a guide to learning physics.

This is a curious thing. Physics has a reputation as something hard to learn. I think – and in truth, this is only speculation – that people see the equations and numbers and weird diagrams of multidimensional space and conclude that a great deal of effort must be invested to make any kind of sense from them.

They may be right. But clearly there is at least some appetite amongst my readers to undertake this difficult task anyway. I thought, therefore, that I’d try to give some advice to those who are thinking about doing so. And though what follows is mostly about physics, I believe it generalises to many hard topics.

Foundations

You don’t run a marathon by getting up one day and running twenty-six miles. No one can do that. And you can’t learn quantum theory by sitting down one day with a copy of Advanced Quantum Mechanics and working through it page by page, either.
The order in which you do things matters. Get up and run a mile before you start thinking about twenty-six. Build a base, so that you are running twenty to thirty miles a week. Start going for longer runs – five miles, eight, ten, and so on, until you are running fifteen or twenty at a time. If you do this, you’ll find your sense of distance subtly shifts. In the beginning a ten mile run seems like a lot – and, in fairness, it is – but once you are able to run six or seven miles, ten seems much more possible. And once you get beyond it, and start running fifteen or twenty, suddenly ten miles feels rather easy after all.
The order in which you do things matters. Build a foundation of mathematics before you leap into the deeper theories of physics. You’ll need to understand calculus before you can grasp electromagnetism; you’ll need to know algebra before you can do calculus.
Part of the challenge is figuring out the right order. As a beginner, how do you know what you need to study quantum mechanics? How much algebra do you need before you can move on to calculus? Fortunately, you are not the first person to tackle this problem. There are guides out there. Universities structure learning to progressively lay down the knowledge you need to go further, and many make this structure publicly available. Textbooks will often tell you the level of knowledge you need to take them on – they might not always be right in this assessment, but if a book says you should have taken a course in classical mechanics before reading it, then find a textbook that covers classical mechanics. And if all else fails, and you run into material you simply don’t understand, then admit this, step back, and seek out the foundation you are missing. Conversely, if things are too easy, then move on to something harder.
Breadth is often better than depth. Mathematics is the foundation of physics, but you don’t need to be an expert mathematician to study physics. Instead you need to know enough to know where the tools are, and where to look up more when you need it. You need to be aware that (e.g.) matrices are a thing, even if you don’t remember every detail about how they work. And you need to know where to go to find that detail if you need it.
Don’t waste time memorising things. Physics is not a subject where you need a great memory or need to recall facts and equations in an instant. Most things can be looked up. You need to build something like a map in your head – you need to know how one thing relates to another, even if you don’t recall the precise relationship. Again, you need to know enough to know where to find more.

Study

Textbooks are the best and quickest way to build theory. Yes, you can (and probably should) watch lectures on YouTube or read blog posts and articles, but these are a complement to good textbooks. When done well, a book takes the reader through a subject in a logical way, presents information clearly, and is more complete than even the most thorough lecture course. Good textbooks, of course, can be hard to find. But there are resources out there that aim to solve that problem too. Never fear abandoning a textbook that simply isn’t good or doesn’t work for you. There are plenty more.
Read, read, then read again. The first time you read a chapter of a textbook you will not understand everything. That is okay. Read until you reach the end or you reach a point at which you don’t understand anything any more. Then read it again. This time pay attention to the places you get stuck. Make an effort to understand what is happening. Look things up; go back to your foundations if necessary. The first pass through gives you an outline. The second gives you understanding. The third puts that understanding in context.

Theory by itself is not enough. It is one thing to read and understand, it is another to put that understanding into practice. So you need to solve problems. You need to use your knowledge in the real world, and put it to work without the guidelines of a textbook. This can be hard. It can feel uncomfortable. If it does, that is a good sign – learning means pushing beyond the boundary of what you already know into the region you don’t. And most of us feel a natural resistance to stepping away from safety and comfort.
Where to find problems? A good textbook will contain problem sets related to the subject you are reading about. If it doesn’t, try related textbooks or university courses. Try re-deriving the proofs shown in the book without looking at them – that is, by working them out on your own.
Work alone at first. When I first started studying I used to do the opposite: the physics students would gather and work together as one big group on a problem set. An answer would emerge, and everyone would present more or less the same solution to the professors. But this was not a serious way to learn. Later, I started working alone. Instead of drawing on the wisdom of the group, I would lock my door and force myself to think about the problem and the solution. This was hard – it took me much longer to find the answers – and it was sometimes frustrating. But I learned more this way. It forced me to go back and really understand the root of the problem. And sometimes I would find a solution that no one else had.
Don’t be tempted to ask ChatGPT for help, or to Google your way around a tough problem. Stick with it. And don’t look at the answer key for “hints”.

Feedback and Shortcuts

It is often tempting to think a list of textbooks and access to the Internet is enough to learn something. But it isn’t. Think about a language. You study the book and do the exercises. But how do you speak in practice? If you go to a bakery in France and start speaking textbook French, then two things will happen. One, your pronunciation will certainly be wrong, or at least mark you out as someone who learned from a book or a tape. And two, you won’t speak like a native, and you’ll get confused when the baker throws back some perfectly common but technically incorrect expression at you. So the book alone is not enough. You have to take your skill into the real world and use it among other people.
After study, you need feedback. People who purely work alone tend to drift into building elaborate theories and models that fall apart as soon as they are exposed to an outside view. To avoid this, you need to expose your work to others, and you need to do this often.
In practice, this means finding others to study with you. Universities offer many ways to do this. Students attend lectures as a group and move through the material at the same pace. Seminars offer a way to talk and discuss ideas. Tutorials give feedback in small groups. If you are studying by yourself this will be harder to do. The best way is to find a committed friend to study with you. But there are also many online communities. Tools like ChatGPT may be able to help, but they are often sycophantic and unwilling to give you the hard feedback you will sometimes need.
You need feedback to catch errors. But you also need it to gather tacit knowledge, the things that everyone knows, but no one writes down. The purpose of a degree in physics is not merely to teach you a set of equations and laws that give you the power to predict the future, but also to teach you how to think like a physicist. And this is not something obvious – there is no course on this. It is instead something you pick up by osmosis, a kind of tacit understanding that spreads by human interaction.
Studies of chess grandmasters have found they rely on intuition more than deliberate reasoning. How do you build intuition? In chess you do it by playing a lot of games and studying a lot of past games. Essentially, you need experience, but you need the kind of experience in which you are repeatedly exposed to similar problems and learn the common patterns that link them. Same in physics. You need to do enough exercises that you start to learn the landscape and build intuition. In time you’ll realise that many problems are similar to one another or can be tackled with a similar framework, even when they initially look completely different. The only way to build this is by solving a lot of problems.
Look for shortcuts. Physics is full of them. Some are mathematical tricks; others are about framing problems in the right way. Indeed, a lot of problems that at first look almost impossible can be rendered simple by switching to a different frame of reference. For some reason, though, I have found few good lists of all the shortcuts and tricks out there. So keep track of the shortcuts you encounter along the way, and never underestimate how useful they can prove.

The Week in Space and Physics: The Lost Sisters of the Pleiades - The Quantum Cat

2025-11-25T16:30:54.000Z

The Pleiades, captured by Starhopper and shared under CC BY-SA 4.0.

Of all the clusters of stars in the night sky, the Pleiades are perhaps the most famous. Humans have watched them for thousands of years. Ancient paintings of them on cave walls might represent our first forays into astronomy and science, or at least into the art of tracking the seasons and the flows of time.

Naturally, then, there are a great number of stories about them. Cultures across the world have told how the stars of the Pleiades were once sisters fleeing from peril, and that to save them the gods lofted them into the sky and affixed them there for all eternity. But in many of these tales one of the sisters is lost, and so today we see only six stars where once there were seven.

So widespread is this story, even across groups of people separated by vast distances, that some think it may be one of the oldest myths of our species. And indeed, over the past hundred thousand years one of the stars really has disappeared. It has drifted behind another, and to human eyes these two now appear as one.

In time, the sisters of the Pleiades will lose each other entirely. The cluster from which they were born, roughly one hundred million years ago, is dissolving. Like all such clusters, it is expelling its gas under the gentle pressure of stellar winds and the violent shocks of massive supernovae. Its stars are being swept by immense galactic tides that are slowly stretching the cluster out into a long stream.

Recently, as telescopes like Gaia and TESS have mapped out the millions of stars that lie around us, astronomers have started to look at how this process is playing out. Several clusters close to Earth, they have found, seem to have formed around a similar time and in a similar place, and are therefore probably linked to the Pleiades.

In blue are the original stars of the Pleiades, shown against the plane of the Milky Way. In yellow are the stars now thought to have formed together with it. NASA’s Goddard Space Flight Center; background, ESA/Gaia/DPAC; Boyle et. al. 2025

A new study has strengthened this idea. By looking at the properties, orbits, and probable ages of nearby stars, its authors have identified thousands that seem to have been born with the Pleiades. These sisters – and they number over three thousand – are now scattered across the night sky, and cover a region more than a thousand light-years across.

Many of these stars also show the chemical characteristics of the Pleiades. They are distinct in how much magnesium and silicon they contain, a fingerprint that comes from their parent cloud of gas and dust. Put together – orbits, ages, and chemicals – this all strongly suggests these stars emerged from the same place.

Astronomers have named this loose collection the Greater Pleiades Complex. It is slowly dissolving, and will continue to do so for tens of millions of years to come. Eventually it will be lost entirely, and the sisters of the Pleiades will be scattered forever across the hundreds of billions of stars in our galaxy.

A Black Hole Superflare

Astronomers call them transients. Every now and then an object in the night sky suddenly brightens, shines strongly for a few days or weeks, and then fades away. Sometimes these are supernovae, giant stars exploding and releasing powerful bursts of energy in their final moments. At other times they are smaller novae, jets from unstable stars, or the result of violent collisions between stellar beings.

Back in 2018, one of these transients was picked up by an automated survey. Initial studies had found nothing particularly interesting about it. But in 2023, after noticing that the object had faded less slowly than expected, astronomers decided to take another look.

That revealed something surprising. The event had taken place at an enormous distance, and the responsible object lay at least ten billion light-years from Earth. For it to be visible from such a distance it must have been incredibly bright and that means it must have been something spectacular and violent.

Studies after 2023 showed the object was probably a black hole, and that the burst of light came from a star in its vicinity. The intense warping of a black hole can sometimes magnify light and make things seem brighter than they really are. But according to the authors of a recent study into the event, that doesn’t seem to be the case here.

Instead, they think the burst came from a star ripping apart as it approached the black hole. It was probably a massive star, one with at least thirty times the mass of the Sun. As it ventured towards the black hole powerful tides would have swept across it. Eventually they become too much for it to survive, and the star was torn apart in a “tidal disruption event”.

We have seen such events before, but this one was the most energetic ever spotted. That means it was probably the largest star we’ve ever witnessed falling into a black hole. Astronomers, of course, plan to keep watching it: as the event has not yet faded away, remnants of the giant star are probably still spinning around the black hole. Over the coming years they should slowly be consumed, and the transient – barring a few more outbursts – should finally fade away.

Blue Origin Dreams Big

On November 13, Blue Origin sent a pair of spacecraft towards Mars. The duo, which together form a single mission known as Escapade, will study how the solar wind interacts with the weak magnetic field around the Red Planet.

For Blue Origin the launch was a triumph. It was only the second flight of the New Glenn rocket, and for the first time the company managed to steer the rocket’s booster back to a safe landing on a waiting barge. This now paves the way for Blue Origin to start reusing rockets, and thus provide a real competitor to SpaceX’s Falcon rocket.

The New Glenn booster stands on the recovery barge as it returns to shore. Credit: Blue Origin.

But Blue Origin is not stopping there. The next flight of New Glenn will target the Moon, and will carry the company’s first lunar lander. Blue Moon is designed to carry cargo to the lunar surface – that might be, for example, rovers, supplies for future missions, or other scientific experiments. If the company succeeds in putting it down safely, they will move on to testing a crewed version.

In this, too, Blue Origin is hoping to rival SpaceX. At the moment, NASA’s plans for the Moon rely on SpaceX’s Starship. But development of this enormous rocket is proceeding more slowly than hoped, and America’s politicians are starting to talk about finding an alternative.

Blue Origin is targeting a lunar landing for January 2026, and plan to follow that with a demonstration of the crewed version by 2027. If they succeed, SpaceX might well start to feel some pressure.

A Stunning Solar Show

A series of solar flares erupted in mid-November. Each was powerful, and one of them – on November 12 – was among the strongest of the decade. Alongside these flares came coronal mass ejections, each a cloud of solar material sent hurtling out into space. As they hit the Earth, they created vivid auroras, some of which were visible as far south as Mexico.

The flares had some minor consequences on our technology. The European Space Agency warned of disruption to satellite navigation services. Radio communications were badly affected across Europe and Africa. The launch of Escapade to Mars was postponed by a day: NASA feared the spacecraft might be damaged by the passing storm.

The Sun is still near the peak of its eleven-year-long cycle of activity. The number of visible sunspots is often used to track this cycle, and that reached a peak only in August last year. Numbers are now falling, but remain high. Nevertheless, the Sun should calm down over the next few years.

From NOAA, the number of sunspots seen over the past decade. Numbers peaked in mid-2024, they are now falling. In pink are the projected numbers for the years ahead.

Issue No. 345 - The Orbital Index

2025-11-19T00:00:00.000Z

Orbital Index is taking next week off for American Thanksgiving. Happy turkey / turducken / tofurky day, everyone! 🦃

The Orbital Index

Issue No. 345 | Nov 19, 2025

🚀 🌍 🛰

¶Data centers, in space, in the news.

While not particularly new or groundbreaking, the concept of moving energy-intensive AI (and other) compute to space is having a moment. On one hand, SSO and high orbits provide far more hours of sunlight than are available on Earth, and having the infrastructure there reduces terrestrial energy and water use issues. On the other hand, GPUs are high CAPEX with short useful lives (possibly necessitating upgrades in orbit), and dissipating all of the waste heat generated during computation will be challenging in the vacuum thermos of space. Nonetheless, numerous orgs are piling on.
NVIDIA-backed startup Starcloud has a first test launch, in collaboration with infrastructure provider Crusoe, NET late 2026.
Jeff Bezos, Eric Schmidt (who now owns Relativity Space), and now Elon Musk have all expressed interest. Elon recently replied to an Ars article about space-based data centers with, “Simply scaling up Starlink V3 satellites, which have high speed laser links would work. SpaceX will be doing this.”
Not to be left out, Google took the wraps off its Project Suncatcher, a study into a constellation of solar-powered satellites hosting AI compute infrastructure with laser crosslinks to scale machine learning. A preprint paper describes models of high-bandwidth intersatellite links, dynamics of sun-synchronous orbits for near-constant sunlight, and studies into the radiation hardness of Google’s AI-focused Tensor Processing Units (TPUs). To achieve the required inter-satellite bandwidth, they propose flying satellites in very close proximity (potentially sub-kilometer, their study looked at just 100-200m separation). Google also tested their TPUs in a 67MeV proton beam, finding irregularities after a cumulative dose of 2 krad, which they say is 3x the expected shielded five-year mission dose (although we wonder about the required level of shielding might be). Google projects launch costs below $200/kg by the mid-2030s, which we also anticipate. “At that price point, the cost of launching and operating a space-based data center could become roughly comparable to the reported energy costs of an equivalent terrestrial data center on a per-kilowatt/year basis.” We’d love to see more about their thermal analysis. Google is partnering with Planet for a test mission of two prototype satellites NET early 2027.
Alternatively, we could transmit solar energy collected in space down to Earth, where upgrading GPUs is easy, no radiation shielding is required, and energy can be used where it’s most needed. This vision of space solar energy for Earth is being pushed forward by companies like Aetherflux, Virtus Solis, Space Solar, and Overview Energy, a startup which Andrew co-founded—more on Overview soon!

Starcloud’s vision of data centers, delivered by Starship, as shipping containers in space.

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¶New Glenn mission NG-02 sticks the landing. After terrestrial and space weather delays, the usual wayward downrange boat, along with a hold or two, Blue Origin’s second New Glenn mission launched. The heavy-lift rocket climbed into the Florida skies, successfully set its high-efficiency second stage on course for an escape trajectory, and returned its booster to the autonomous drone ship Jacklyn (landing video). New Glenn, weighing ~1,650 tons when fueled, has a stated payload to LEO of 45 tons, roughly double that of Falcon 9 (which weighs in at 550 tons) and similar to Falcon Heavy (1,420 tons). New Glenn’s first stage is 16+ meters taller than a Falcon first stage, making this landing the largest booster ever to land at sea (Starship’s 52 m upper stage has splashed down, but will eventually be caught by a land-based tower when mature). Despite the size difference, Jacklyn/LPV1, New Glenn’s landing pad droneship, is only slightly bigger than Falcon 9’s due to NG’s ability to deep throttle, hover, and translate into position, unlike F9’s hoverslam. Jacklyn is equipped with a robot that performs safing and 6 robotic transport stands that secure the booster to the ship. Additionally, immediately after landing, the booster explosively welds (patent) itself to the deck (rather than doing this). Blue is hoping to reuse this booster (named Never Tell Me the Odds) on its very next flight, which the company is currently aiming to have happen early next year. The mission’s payload was ESCAPADE, two spacecraft that will study the Martian magnetosphere and how its atmosphere has been stripped by the solar wind over time (also useful to understand if we’re ever to try terraforming the red planet). ESCAPADE was managed (under budget!) by UC Berkeley Space Science Lab and built by Rocket Lab. Due to New Glenn not being ready, the mission missed its original launch window last year. So, while we’re not currently in a Mars transfer window, New Glenn was available now (and maybe so was the NASA budget…), so ESCAPADE will loiter around Earth-Sun L2 (not Cleveland) for about a year before flying back near Earth for an efficient burn deep in our gravity well before heading on to Mars. (Related: New Glenn’s comparatively quick success with recovering boosters isn’t likely to trouble SpaceX in the near term, which has been landing rockets for 9 years and just completed its 500th mission with reused rocket boosters, but may spell trouble for ULA, to whom Blue just delivered another set of new BE-4 engines.)

Never Tell Me the Odds’ GS-1, landed and welded to Jacklyn’s deck, with banana-colored humans for scale.

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¶News in brief. Yet more in-space manufacturing news: Atmos Space Cargo and Space Cargo Unlimited will launch the first of their planned seven orbital manufacturing research and reentry missions next year ● Rocket Lab (unsurprisingly) delayed Neutron’s debut to 2026 to continue qualification testing ● In a move that definitely won’t lead to any future confusion, Project Kuiper has been rebranded to Amazon Leo ● French satellite manufacturer U Space raised a $27.8M Series A to ramp up production ● ISRO completed a parachute air drop test for the crew module for their upcoming first crewed Gaganyaan mission, currently NET 2027 ● One of the DSN antennas in California has been offline for months after it was damaged by over-rotating, which stressed cabling ● North Carolina-based Extellis raised an $6.8M seed round to fund their first demo imaging satellite ● Infinite Orbits secured a $46M round of investment from multiple partners across the EU to accelerate the deployment of a fleet of inspection and life-extension satellites for European GEO assets ● Shenzhou-20 astronauts safely returned to Earth on the recently launched Shenzhou-21 vehicle after orbital debris cracked a window on their original return vehicle (c.f. Issue 344), leaving the Shenzhou-21 crew without an escape/return vehicle until Shenzhou-22 launches in the near future.

Recovery efforts to extract Shenzhou-20 astronauts from the Shenzhou-21 return module after touching down in Inner Mongolia.

¶Jobs.

Pioneer Labs is hiring an Operations Associate in Emeryville, CA. Pioneer is “building the first microbes that can turn Martian dirt, water, and air into the building materials needed to sustain life in the low-resource environment of the red planet,” so that’s pretty darn cool.

¶Etc.

TerraWatch’s Aravind Ravichandran shared his opinion on ‘Why "Science-as-a-Service" doesn't work for Earth Science.’
In case we haven’t linked it before, the Armagh Observatory has a fun series on the largest rocket concepts that never made it to the pad (parts 1, 2, and 3).
Ars reported recently on Russia's 15-year project to finish construction of the Vostochny spaceport, a development project deeply marred by hunger strikes, unpaid workers, purges of top officials for corruption, theft of $126M, and “a man driving a diamond-encrusted Mercedes [who] was arrested after embezzling $75,000.” Now, the contractor building the spaceport has failed to pay its energy bills (~$600k), and power has been shut off to under-construction areas of the spaceport, with the contractor possibly heading into bankruptcy. Russia hopes to launch its newest launch vehicle, Angara, from this facility in the future, allowing it to phase out the aging Proton.

The Sun is at or near solar maximum. Multiple CMEs arrived at the Earth last Tuesday, causing a large geomagnetic storm with aurorae visible as far south as Florida in the US. While originally predicted to be a G5 storm, it turned out to be a G4 event. Relatedly, a CME was recently observed for the first time around another star. Below is a GOES-19 capture of the X5.1 flare that caused the aurorae.

The Biggest Solar Flare of 2025 - The Quantum Cat

2025-11-14T14:31:02.000Z

The aurora over Missouri. Smuckola, shared under CC-BY-SA-4.0.

In some ways it is surprising this doesn’t happen more often. Every now and then, a piece of the boiling, bubbling, nuclear furnace we call the Sun escapes out into space. Most of the time this is harmless enough: the solar system is a big place and Earth makes up very little of it. But sometimes it isn’t. Sometimes the Earth lies in the path of whatever the Sun has decided to hurl at us.

This kind of thing usually starts with the appearance of a sunspot. These dark blemishes sporadically mar the surface of our star, and tend to cluster in groups known as active regions. They look dark because they are cold, or at least cold compared to the rest of the Sun, and so they shine a little less brightly than their surroundings.

Why they appear is not yet fully known. But we do know they are linked to the Sun’s magnetic field, and that this field can sometimes tie itself up in complicated knots. Where these fields emerge from or enter into the Sun they exert a pressure pushing down and so prevent heat from welling up as fast as it normally would. This results in a cooling spot on the Sun, and since these magnetic knots form complex structures which can enter and emerge from the surface in many places, these spots often appear in clusters.

All of this, of course, involves a great deal of energy. Most of this is stored in the magnetic field, and it must eventually be released. Often this happens calmly: the knots gently relax, the flow of heat increases, and the sunspots fade away. But it can also happen violently as magnetic field lines snap and reconnect.

Sudden releases of energy like this create flares. First, the energy accelerates subatomic particles and sends them crashing through the solar atmosphere. That creates a flash of radio waves, X-rays and high-energy gamma rays. These burst away from the Sun at the speed of light, and wash over the Earth within minutes of the eruption.

Alongside these intense flashes of energy, flares can sometimes release clouds of solar material known as coronal mass ejections. Again, we don’t know exactly why this happens or why these are so often linked to flares, but it is this material that is sometimes aimed at Earth. And though these travel fast, they are slow compared to the flare itself. While a flare can reach the Earth in minutes, a coronal mass ejection takes days.

Over the past week, an active region on the Sun labelled AR 4274 has flared up at least four times. Each of these flares was big enough to reach the top “X-class” on the scale used by astronomers. Wednesday’s was the biggest of the year so far, and one of the strongest to erupt this decade.

The first three flares sent coronal mass ejections heading towards Earth, and so treated people across the world to glowing displays of the aurora lighting up the skies. As with other strong magnetic storms, these aurora were seen much further south than normal, and most notably over the Americas and Europe, where they reached as far south as Mexico and Italy.

Fortunately, such things are not directly harmful to us. The Earth is protected by a magnetic shield, and the lights we see in the sky come from particles moving through this invisible barrier. But they can and do impact our technology.

Satellites are vulnerable to the radiation and swings in magnetic fields. The European Space Agency warned of disruption to satellite navigation services. Radio communications were badly affected across Europe and Africa. A planned launch to Mars was postponed: NASA feared the spacecraft might be damaged by the passing storm.

The inevitable comparison, of course, is with the events of September 1859, when a truly colossal flare and coronal mass ejection swept over the Earth. That storm was probably ten times the strength of the one that hit us this week. But it is not the only major solar event of the past two centuries.

Notably, one in 2003 was powerful enough to overwhelm monitoring satellites and damage electrical grids on the ground. Another, probably comparable in size to that of 1859, was seen in 2012. It fortunately missed the Earth – had it struck, the damage might have been catastrophic.

There is no reason to think of the flare of 1859 as an upper size limit. They can probably get bigger, maybe much bigger. How much so is uncertain. The mechanisms behind flares and solar storms are still not well understood, and so this is mostly a question of looking at the historical record. But people haven’t always kept good observations of the aurora, and even if they knew what to look for, cloudy nights can mean even the best observers miss them.

Trees, however, have kept decent records. A particular isotope of carbon is created in the atmosphere during flares, and this is taken up by trees and laid down in their rings. Careful study of old trees, it turns out, can reveal the history of our star.

This work hints at big flares in the past. One seems to have hit around 770 AD, another in 993. Yet the records are patchy, and tree rings aren’t always easy to decipher. Astronomers struggle to say how big these flares were, or even if they were caused by the Sun or were actually some other rare cosmic event.

An alternative is to look at other nearby Sunlike stars. Instead of studying ten thousand years of history, we can monitor ten thousand stars over a single year. These studies have revealed something frightening: flares can indeed get big, far bigger than anything we’ve ever observed. Some stars emit superflares, each a hundred or a thousand times the size of the 1859 event.

Fortunately, they seem to be rare. Sunlike stars emit a superflare once every few hundred years. It could be one of these that struck in 770 and 993. Back then, it would only have sparked dramatic auroral displays in the skies. Today it would wreak havoc on our satellites and connected planet. Still, at least we’d have some pretty lights to admire before the power went out.

Issue No. 344 - The Orbital Index

2025-11-12T00:00:00.000Z

The Orbital Index

Issue No. 344 | Nov 12, 2025

🚀 🌍 🛰

¶More orbital manufacturing news. Following our recent coverage of Besxar Space Industries and their use of returning Falcon 9 boosters for in-space manufacturing development, it’s worth mentioning a bunch of other recent in-space manufacturing updates. While the market doesn’t exist today, many companies hope to create it.

Beleaguered Momentus received a $5.1M contract from NASA’s Flight Opportunities program for their Vigoride OTV to host the Commercial Orbital System for Microgravity In-Space Crystallization (COSMIC) experiment. COSMIC, from SpaceWorks and Astral Materials, will explore growing higher-quality and more consistent semiconductor crystals than can be grown terrestrially.
Varda signed an agreement for 20 more manufacturing spacecraft landings at Australia’s Koonibba Test Range and a joint development agreement with United Semiconductor to produce semiconductors in orbit. Varda will also now operate two spacecraft simultaneously for the first time, with the launch of their fifth capsule on Transporter-15, joining their fourth mission still in orbit.
UK-based SpaceForge, which raised a $30M Series A in May and launched its ForgeStar-1 in July, has formed its own partnership with United Semiconductors for in-space semiconductor manufacturing.
In China, ground tests were completed on a 2-meter-diameter cylindrical inflatable module for in-space manufacturing of “biopharmaceuticals, 3D printing, and the production of novel materials.”
LambdaVision raised a $7M seed round to scale up manufacturing of artificial retina implants by using the LEO microgravity environment to control surface tension, sedimentation, and convection-driven buoyancy. This allows for precise material deposition during the manufacturing of their precision nanomolecular devices. LambdaVision has previously flown nine times to the ISS and produced a 200-layer protein thin film artificial retina precursor.

LambdaVision’s artificial retinas use carefully deposited alternating layers of bacteriorhodopsin and an ion-permeable membrane. Bacteriorhodopsin is a light-activated protein that acts as a proton pump. “The layers are repeated multiple times with the aim of absorbing enough light to generate an ion gradient that can stimulate the neural circuitry of the bipolar and retinal ganglion cells within the retina.” Bacteriorhodopsin derives from Halobacterium salinarum, a microorganism belonging to the Archaea domain found in hypersaline lakes—an ancient form of life. As always, basic science, especially in ecosystem biology and non-model organisms, pays unexpected dividends many years later. See also: CRISPR (weird repetitive DNA sequences in E. coli that turned out to contain snippets of viral DNA), PCR (uses a heat-stable enzyme isolated from a hot spring extremophile bacterium), and GLP-1 (in part based on a peptide from Gila monster saliva). Credit: LambdaVision

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¶Shenzhou takes a hit. Just as the new three-person Shenzhou-21 crew arrived at Tiangong station for their six-month stay, the return of the Shenzhou-20 crew, which they were meant to relieve, was delayed to assess the safety of their return craft after a suspected space debris impact. The Shenzhou-20 crew has already spent six months on the station, which is only designed to support more than three taikonauts for short periods. China does have the Shenzhou-22 capsule on standby and could launch it in short order (possible as soon as eight days), allowing the S-20 crew to return on S-21’s craft and a replacement to arrive shortly after for S-21’s eventual return. Once again, Musk has been called on to ‘rescue’ the delayed (not stranded) crew, much like the theatrical retrieval of the Starliner demo crew from the ISS—however, there’s an exceptionally low likelihood that such an operation could even begin to be feasible due to the Chinese station’s orbit, docking differences, and spacesuit incompatibility, let alone the political implications and impact on future Dragon missions (SpaceX does not have an unassigned fleet of Dragons on standby, so would have to reallocate another customer’s spacecraft for retrieval). This is the second debris hit on a crew vehicle in recent years (Soyuz MS-22’s radiator was struck in 2022, necessitating the launch of a replacement vehicle to the ISS), underscoring the growing problem of space debris as discussed last week. It also highlights the need for international standardization of items like docking adapters and suit interoperability. (ESA may require them to all charge via USB-C?) While unlikely to be needed for this mission, as private stations proliferate, the need for a rescue mission, conducted using whatever crew vehicle is available, seems eventually inevitable.

The crews of Shenzhou-20 and Shenzhou-21 during a handover ceremony prior to the delay of S-20’s return. It’s going to get a bit cozy up there.

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¶News in brief. Jared Isaacman is so back—after much consternation and some leaked memos, Trump re-nominated Isaacman to the Senate for confirmation as NASA Administrator, to a mostly enthusiastic industry response ● Due to the government shutdown, the FAA restricted commercial space launches to evening hours (which delayed Transporter-15 among other missions), citing air-traffic control staffing limitations ● Blue Origin scrubbed their New Glenn launch of ESCAPADE to Mars due to weather—they are scheduled to try again today ● Intuitive Machines made a bid to buy the recently renamed Lanteris Space Systems (fka Maxar Technologies’s satellite manufacturing arm, taken private by PE in 2023) for $800M ● An Ariane 6 launched the Sentinel-1D EO radar imaging satellite, which will replace Sentinel-1A to complete the Sentinel-1 mission (continuing the vehicle’s quick ramp up in launch cadence) ● China launched a Long March 11 and a commercial Kinetica-1 from CAS Space, surpassing its annual record with 70 launches ● In-space power beaming startup Star Catcher demonstrated ground-based delivery of 1.1kW to commercial off-the-shelf solar panels using multi-wavelength lasers, breaking DARPA’s previous record of 800W ● Senegal started construction of an optical astronomical observatory, the first of its kind in West Africa ● EchoStar is selling more spectrum to SpaceX for $2.6B in stock to support the company’s US direct-to-cell services ● A Galactic Energy Ceres-1 failed to reach orbit after its fourth stage shut down prematurely, marking the second failure out of 22 launches for the Chinese commercial launch company ● Bloomberg Philanthropies announced the investment of $100M to accelerate efforts to reduce methane emissions with some funding allocated to expanding existing monitoring satellite constellations such as Carbon Mapper ● Rick Hauck, NASA astronaut who commanded the first post-Challenger Shuttle mission, passed away at 84

STS-26 commander Rick Hauck, floating on the middeck of Discovery, beside a portrait and mission patch honoring the fallen Challenger crew. RIP.

¶Etc.

NASA may be quietly gutting an iconic campus with what it calls strategic closures, workers fear: ‘Furloughed employees were given just days to temporarily return to work and help empty entire buildings of highly specialized equipment, according to sources and internal emails obtained by CNN. In the communications, NASA managers wrote that equipment not moved in time — including one-of-a-kind hardware — could be thrown away or donated.’
Blue Sky Space, a UK-based startup, will soon launch Mauve, a 16U cubesat with a 13 cm UV telescope, and plans to sell its astronomical data via a subscription priced roughly equivalent to 1 PhD salary/year.
NY Times: How Lunar Photography Brought the Heavens Down to Earth.
Joining ESA’s ExoMars and Mars Express, CNSA’s Tianwen-1, orbiting Mars, imaged interstellar object 3I/ATLAS at a distance of ~29 million km.
A reader shared their free-to-use API (docs) with 1.18M pre-analyzed landing sites at the lunar south pole, built on NASA LOLA and LROC data. The sites scored on metrics including slope, illumination, elevation, comms line of sight, and proximity to resources.
As Canada and Europe push for domestic launch markets, the limitation may be experience, not capital. With ~$600M in funding, German company Isar has “attracted more investment than Rocket Lab, Firefly Aerospace, and Astra collectively raised on the private market before each of them successfully launched a rocket into orbit.”
Space Elevator. Wee!

The ISS celebrated 25 years of continuous habitation last week—a quarter century highlighting the immense ability of our species to accomplish great things when we work together instead of picking fights. Here’s what it looked like in September 2000, just before the first of a long line of crew members occupied it beginning November 2nd, 2000. Credit: NASA

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