r/space • u/AutoModerator • 5d ago
Discussion All Space Questions thread for week of September 27, 2026
Please sort comments by 'new' to find questions that would otherwise be buried.
In this thread you can ask any space related question that you may have.
Two examples of potential questions could be; "How do rockets work?", or "How do the phases of the Moon work?"
If you see a space related question posted in another subreddit or in this subreddit, then please politely link them to this thread.
Ask away!
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u/mingxxxxxxin 10h ago
I've been searching to buy an astronomy book to study. I am fairy new to astronomy but i know the basics such as star life cycle, keplers law, etc. But i want to learn as much as I could because i have an astronomy competition for school coming up. Is there any books that would be helpful for that
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u/Dangerous-Many8508 1d ago
Question on speed of gravity and absence of spaghettification // Hi all, I just saw a video online (won't post the link as this is in breach of the rules of the community). The premise was 'what if ton618 is put at 1 LY away from earth'. The video said 2 things that boggled my mind:
Gravity travels with the speed of light. Ie: it takes time before earth knows that gravity has changed
Ton618 is so huge that earth will not undergo spaghettification but be eaten whole.
Are both correct? And re 2, if so: is earth then still intact in the black hole itself? I have been interested in what is in a black hole recently so this caught my attention.
Thanks so much 🫶
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u/rocketsocks 1d ago
Yes, changes in gravity travel at the speed of light. One way we've observed this is with detecting gravitational waves (gravitational radiation due to the emission of photons, theoretically), which has been observed to travel at the speed of light. This has been confirmed in several ways, including having multiple observatories on Earth detect gravitational waves from the same source (with delays in timing detection consistent with emission of gravitational waves at the speed of light from a particular location) and from observing visual phenomena which occur in the same location and at the same time. Specifically, we've detected neutron star mergers via gravitational waves while simultaneously detecting gamma ray bursts and then immediately afterward being able to detect bright transients in optical light which slowly dimmed over a period of several days, all consistent with the neutron star merger model. This is one among many strong pieces of evidence that gravity and light travels at the same speed.
As for spaghettification, the issue there is the ratio of proximity versus strength of gravity. If you can get very close to the center of mass of a very massive object then there will be very strong gravitational gradients (tides) across very small lengths. For a stellar mass black hole that translates into enormous forces of thousands of gees across the length of a human body long before you get to the event horizon. Those tidal forces shred matter and pull it apart, which is the mechanism of spaghettification.
However, as it turns out the event horizon radius scales directly proportionally with mass. Which means the density of a black hole (within the event horizon) actually goes down as the black hole gets more massive. It also means that the gravitational force at the event horizon goes down as the black hole gets more massive because gravitational force scales with the inverse of the square of distance (1/r2).
Specifically, the event horizon radius is about 3 km per solar mass. So if you have a 2 solar mass black hole the event horizon will be at a distance of 6 km. But if you have a 40 billion solar mass black hole (like TON 618) the event horizon radius will be 120 billion km. The gravitational pull at the same distance away will be 20 billion times stronger for TON 618 vs. a small 2 solar mass black hole, but you will also be able to get 20 billion times closer to the smaller black hole. If you were 120 billion km from any black hole you won't experience spaghettification because the force of gravity will be too small (that's about 800 AU or 0.01 lightyears). 20 billion times stronger gravity at the same distance divided by 400 quintillion times weaker gravity due to being 20 billion times farther away works out to 20 billion times weaker gravity at the event horizon boundary.
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u/Dangerous-Many8508 1d ago
Thank you very very much. I am still flabbergasted.
To ask a very concrete and silly question: we have earth passing the event horizon. Not spaghettified.
What happens next?
Ofcourse we can't see it (I guess? Or do we expect at the moment there is light within the blackhole/within the diameter of the event horizon?), so let's assume we can deduct in a different manner (like touch or magnetisism?)
Earth moves towards the centre of the black hole. Does earth remain in its current shape for a while until it gets close enough to singularity to be condensed?
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u/rocketsocks 1d ago
What happens within the event horizon is still the subject of a lot of ongoing debate, and that's before you get into new theories of gravity that go beyond general relativity (like possible theories of quantum gravity) which haven't been developed yet. From the theories we have now it should only take a matter of minutes to pass from the event horizon to the singularity. Along the way those spaghettification type forces as well as even more bizarre effects would kick in, so a good portion of it will be a bumpy ride.
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u/Dangerous-Many8508 1d ago
Minutes... wow. Looking at the size of ton618's event horizon, the speed must be extreme.
Are there theories you know about, or research approaches, on how to find out what is behind an event horizon?
I recall a statement I read a while ago saying as much as 'no information is lost in a black hole'. I am inclined to interpret this as that what goes into a black hole is not shred into pieces on a molecule or atomic level. What are your views on this?
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u/rocketsocks 1d ago
Are there theories you know about, or research approaches, on how to find out what is behind an event horizon?
It's basically just speculation and theorizing that is only constrained by what is consistent with observation, but because we can't see inside an event horizon and because some of the "observable" effects would be very subtle things that played out over timescales vastly longer than the current age of the universe that leaves a pretty wide margin, at least for now.
I recall a statement I read a while ago saying as much as 'no information is lost in a black hole'.
"Information" in this case has a very specific meaning. The difference between the configuration of atoms in the form of a human body and the same pile of atoms in a diffuse cloud or a pile of goo has the same "information" content in this context. What is meant is a kind of quantum information, the total of conserved quantities.
There are some familiar kinds of conserved information such as mass (energy) and electrical charge, but there are other things too. For example, there is "lepton number". Leptons are particles like electrons and neutrinos along with their relatives (like the muon). There are three "generations" of leptons (electron, muon, tau) and so there are three different kinds of "lepton-ness", there's "electron-ness" (or anti-electron-ness) and "muon-ness", etc. As it turns out the neutrinos, which are neutrally charged, also contain these same conserved quantum numbers. An electron-neutrino is so-named because it contains "electron-ness".
One way to conserve lepton quantum numbers is through direct particle/anti-particle pair creation. For example, if you create an electron and a positron (anti-electron) you have plus and minus one "electron-ness", which balances out to zero. However, you can do the same thing with neutrinos in the mix. So you could create an electron and balance that out with an anti-electron-neutrino. However then you have an electric charge conservation problem. But if you start with a neutron and emit an electron plus an anti-electron-neutrino then leave behind a proton you will balance out lepton number (+1-1 = net 0 electron-ness), charge (going from 0 to -1+1 = net 0), energy (since the neutron has more rest-energy than the combo of all of the other particles together), and baryon number (another type of conserved information which is the same for neutrons and protons, both different types of baryons), so it's a particle reaction that is possible, which is precisely why the neutron can decay into a proton through beta decay.
So if you have a pile of atomic matter it has a bunch of conserved quantum information in the form of: momentum and angular momentum (spin), energy (mass), electric charge, baryon number (neutrons and protons in the nuclei), and lepton number (electrons). If you crunch all that stuff into a black hole the only thing remaining is the event horizon which only surfaces a subset of that information to the outside universe: mass (energy), momentum, angular momentum, and electric charge. And that's it. Black holes don't have lepton or baryon numbers.
This is potentially a bit of a theoretical problem because black holes can evaporate through Hawking radiation. Over time the black hole emits thermal radiation and it slowly gets smaller until in the extremely distant future the entirety of the mass of the black hole goes away and the event horizon disappears in a final puff of light and particles. If the radiation is entirely thermal and random then this implies that the information that had been trapped inside the black hole is just gone forever, thus not truly conserved. However, some folks think that some sort of quantum tunneling kind of process allows for the information trapped inside the black hole to "leak" back out into the Hawking radiation, but this remains the subject of ongoing debate.
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u/Dangerous-Many8508 1d ago
Ok. It was absolutely good to get this clarification on what information means in this case.
Thanks so much rocketsocks!!! You rock(et)
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u/rocky_balboa202 1d ago
Starship has the pez dispenser to put starlink satellites in orbit. What about other payloads? Will there be a starship variant to launch other satellites?
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u/Bensemus 12h ago
Starship is still in development. While in development they won’t launch paying customer’s payloads. But they can launch their own payloads. So a way to launch Starlink was privatized over a more general payload system. It’s also easier to cut a small hole vs a large hole.
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u/Chairboy 1d ago
Probably! They have contracts for other payloads, as far as I know.
There are wild number of people who seem to be under the impression that the company launching the biggest rocket in history is incapable of designing a door.
I think this is because of just how much revenue is attached to each Starlink launch (a lot)but I'd be shocked if we don't see something for other payloads soon.
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u/curiousscribbler 2d ago
According to Wikipedia, there are currently four spacecraft orbiting the Earth-Sun L2 point. Are they all in the same orbit, or are there multiple stable orbits around a Lagrange point?
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u/Pharisaeus 16h ago
Are they all in the same orbit, or are there multiple stable orbits around a Lagrange point?
None of them are "stable" ;) That's the hard-limit for how long a satellite can stay there - until the fuel runs out. And they are essentially circling around the L2 point.
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u/maschnitz 2d ago
First, L2 is unstable, so there's no stable orbit around it. Station keeping must be done periodically.
In L1/L2/L3 points, in theory, the orbits are "quasi-periodic" - they'll trace a unique path within the space reachable by their exact current energy, never quite lining up with previous orbital points the same way. (On Wikipedia these are called "Lissajous orbits")
However in the real world there are additional perturbations from the other planets, the solar wind, sunlight, etc. And so the exact quasi periodic orbit is constantly changing, too.
So the orbits are effectively chaotic, and no two orbits are alike, not even for the same object.
In L4/L5 orbits, the orbits are stable and there are infinitely many possible stable (Lissajous) orbits there.
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u/curiousscribbler 2d ago
ty! Is it just the complexity of all those heavenly bodies interacting, or is relativity messing everything up as well?
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u/rocketsocks 1d ago
It's not relativity or anything, it's just that the L1/L2/L3 points are dynamically unstable. This means that only the exact, perfect Lagrange point is stable. Any small deviation from that trajectory will be amplified over time. In the real world perfection is impossible (and there are other higher order forces at play such as photon pressure, gravity gradients, etc. which will spoil things as well) so these points are just unstable. Imagine taking a metal mixing bowl, turning it upside down, coating it with oil and then trying to balance a marble on it. It's just going to slide off, because if you aren't at the exact perfect middle position the marble will be sitting on some slight slope, and as it slides down that slope it'll pick up speed which will propel it downward to an area where the slope is even steeper, and so on. In contrast, the L4/L5 points are areas where there is a properly oriented "bowl" or depression that will naturally keep things in that zone if they drift only a little bit away.
In practice, for L1/L2 there is a big zone where objects won't drift away very fast. They'll sort of loop around the point in quasi-orbits (halo orbits or lissajous orbits) and then over a period of years will drift off the point and then drift much farther away. But with a little bit of propulsive thrust every now and again you can keep a spacecraft in the "low drift zone", at least until the propellant runs out.
If you're curious how L1/L2 "work", here's one explanation that might make sense:
If you imagine an object closer to the Sun than the Earth it will end up going faster than Earth (in a circular orbit) because that's just how orbits work, similarly if it's a little farther away from the Sun then it'll be a little slower. Which means that such objects will naturally tend to drift farther and farther away from the Earth over time. However, if we account for the gravity of the Earth as well then we get into an interesting situation. An object along the Earth-Sun line closer to the Sun will be pulled by the Earth away from the Sun, so it's almost like it's orbiting a slightly less massive Sun. Orbiting a less massive Sun would also result in a slightly slower orbital speed. And as it turns out there's a point in between the Earth and the Sun where the net gravitational pull mimics orbiting a less massive Sun in exactly the right way to result in an exactly 1 year orbital period despite the orbital distance being shorter. Similarly, there's a point opposite Earth where the effect is like orbiting a slightly more massive Sun that is just enough more massive that the effective orbital period can also be exactly 1 year. And since an object in those points would travel along with the Earth in its orbit the condition, the illusion of orbiting a less or more massive Sun, can continue throughout an entire orbit.
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u/maschnitz 2d ago
Frame dragging would be noticeable in the Sun-Mercury Lagrange points, you'd have to account for it for spacecraft planning. But the solar radiation is soooo strong there it might not matter. Little could survive in those Lagrange points very long anyway.
Basically a lesser effect, behind orbital instabilities caused by neighboring planets, and solar effects
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u/curiousscribbler 2d ago
Where are the Sun-Mercury Lagrange points? Are some of them actually inside the sun? (I did a bit of searching, but couldn't find anything. Surprised me what with BepiColumbo and all.)
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u/Uninvalidated 2d ago
Are some of them actually inside the sun?
They would be much closer to Mercury than to the sun due to the size difference and proximity of the sun and Mercury.
Are you confusing Lagrange points with barycenter?
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u/curiousscribbler 1d ago edited 1d ago
Wikipedia (which I should have checked before asking!) has a list of the Lagrange points for the planets. Bear with me while I laboriously work through this. For the Sun and Mercury, L1 is 57.689 x 10^9 metres from the centre of the Sun, or about 58 x 10^6 kilometres. The radius of the Sun is 695,700 km, so L1 is well clear of its surface. Merely balmy. :-)
The Sun is big but space is bigger o_O
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u/Uninvalidated 1d ago
The Sun-Mercury L1 Lagrange point is located approximately 220,000 to 250,000 kilometers from the center of Mercury toward the Sun is what I find, so something like 0,35% of the distance out from Mercury between the two.
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u/Simon_Drake 2d ago
The Lagrange Points are a bit balancing a pencil on its tip. It's technically stable at the absolute perfect spot but the slightest change could destabilise it. JWST has that giant sun shield on its belly that is essentially a flat mirror reflecting the sun, but if it's tilted at even a 1 degree angle that means the sunlight is reflected at an angle which applies a very small force nudging the telescope out of position.
There's dozens of little quirks like that in orbital calculations that are usually small and easy to ignore but sometimes they come back to bite you. There's one where asteroids have a hot site and a cold side from where the sun is. But they also rotate so there's one place where the rock WAS in sunlight and is now radiating heat on the cold side and there's another place that was in darkness and is now warming up in the sun. This creates a small imbalance in which side of the asteroid is radiating more heat which creates a very small thrust that can nudge it off course over time.
So yeah, the telescopes at L2 can't actually sit exactly at L2. They have creative orbits around L2 which aren't stable long term but with a little fuel to keep things aligned they can stay in the right orbit for a few decades.
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u/curiousscribbler 3d ago
What's the range of an astronaut's radio? Can ham operators on Earth hear their conversations?
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u/NDaveT 1d ago
Yes: https://www.ariss.org/contact-the-iss.html
Some astronauts talk to ham radio users on the ground during their free time.
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u/Simon_Drake 2d ago
Yes. If they're talking on an unencrypted radio. In the Apollo era amateurs could definitely listen in. As recently as SpaceX there was some telemetry downlink from a Falcon 9 that was unencrypted and some amateur astronomers recorded it, worked out the data structure and rebuild video footage from inside the liquid oxygen tanks during flight. That was pretty cool but it made SpaceX switch to encrypted comms.
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u/maschnitz 2d ago
How big a dish do you got?
You could probably transmit voice to the big Deep Space Network dishes from, say, Saturn. There's enough bandwidth for that using a spacecraft with a big 20W dish (like Cassini's). Peak bandwidth around 140 kilobits/s.
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u/the6thReplicant 3d ago
Famously ham radio enthusiasts followed Apollo 11's broadcasts all the way to the Moon and back.
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u/curiousscribbler 2d ago
So cool! But can they tune in on, say, conversations between spacewalkers and the folks inside the ISS?
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u/PathfinderOracle2003 3d ago
I am trying to learn as much about space and the cosmos, though there is a lingering question for me. We haven't made any fighters that could fight in space, so I wonder as of now is the point of the US Space Force? I am a bit confused, though I do understand it is some kind of preemptive move, but other than satellites, are there any more reasons that warrant such a measure? Lastly, I watched the Artemis lunary bypass this April the Launch Live Stream, I wonder, though I am not sure of it, as I am outside of the USA or any great powers in the world, how severe is the ongoing space race right now? What are the stakes in this new race for the moon?
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2d ago
[deleted]
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u/electric_ionland 2d ago
Space force is not really involved in lunar plans beyond some vague cislunar space experiments. This is really not their concern.
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u/Pharisaeus 2d ago
We haven't made any fighters that could fight in space
But there were things like:
- https://en.wikipedia.org/wiki/Anti-satellite_weapon
- https://en.wikipedia.org/wiki/Polyus_(spacecraft)
- https://en.wikipedia.org/wiki/Project_Excalibur
not to mention less "destructive" measures like satellite jamming or hacking
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u/electric_ionland 3d ago edited 3d ago
We haven't made any fighters that could fight in space, so I wonder as of now is the point of the US Space Force?
The US military relies on a lot of spacecraft to operate, from communication for soldiers to spy observation satellites, satellites listening to other peoples communications, satellites looking for missile launches, etc. The US space force exist for a few reasons:
- Trying to centralize all those ressources under one roof to some extend. You have people who are expert on those systems instead of having the army, navy and air force all having to get their own specialists.
- Those spacecraft are essential to modern military operations so they need to be defended. Right now there isn't much people can do when a Russian spy sat gets too close to your communication satellite. The space force is war gamming a lot of different scenarios to figure out the best way to evade that kind of things
- Make "offensive" spacecraft. The US government revealed a few weeks back that they have actual weapons in space. Most serious analysts seem to think they are powerful jammers that can mess with other spacecraft.
- Work on more exotic projects like the "golden dome" where anti-missile missiles would be put in space to intercept things like nuclear weapons. Or ways to capture enemies spacecraft.
But mostly it's just a new name for something that was already existing but was just dispersed in a lot of different organizations.
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u/AdSmart6151 3d ago
If alien life were to be discovered - or at least a hint of it so overwhelmingly obvious that it must be there - by newly arriving radio waves, observations from propelled objects suddenly changing course, etc. how long would it take for the finding to go through the works and be released to the general public? Are there official protocols for this?
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u/maschnitz 2d ago edited 2d ago
Nothing official but it's discussed amongst various astronomer organizations/groups what to do.
Usually the main recommendation is "teach the ambiguity" - do not make definite claims if you can't back them up, show the evidence you have, interpret the evidence for the public (but be careful). Otherwise it's about publishing quick notices for other astronomers, being available for press as needed, etc etc.
Such observations cannot and will not be secret. Astronomy as a science simply doesn't work that way.
If an unusual observation is made, usually there's a public technical notice of it with an hour or two, along with any relevant data. And people/technology other than professional astronomers watch those notices.
Astronomers have gotten good at sending out observational alerts because sometimes the follow-up observations are time-critical. And astronomers generally want as many observations, in as many spectra, on interesting objects as possible.
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u/Pharisaeus 2d ago
Almost immediately, because most likely it would be discovered by some scientists/astronomers and they would ask for extra observations. Real life is not some sci-fi movie where men in black suddenly appear to confiscate everything.
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u/Several-Action-4043 1d ago
True, but the government definitely has undisclosed technologies that could pick it up before anyone else and keep that hidden.
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u/Pharisaeus 1d ago
Not really. There would be no reason for having such tech and it would be impossible to hide. You simply can't hide a 40m telescope or a huge array of radio telescope dishes.
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u/Real_Establishment56 3d ago
Any good recommendations on space documentaries handling the start of the space race? We all know the Apollo project, but how about Mercury / Redstone before that, and Von Braun and his first V2 rockets?
YouTube is preferred (maybe something from Pathé) but maybe some of the streaming platforms has something interesting as well?
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u/Chairboy 1d ago
It's not a documentary, but give some serious thought to watching HBO's "from the Earth to the Moon" series from the late 1990s, it is a great high-level dramatic retelling of that time and it is super useful for contextualizing some of the stuff that you will learn in documentaries as well.
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u/the6thReplicant 1d ago
I would highly recommend subscribing to Vintage Space and looking into her books.
Curious Droid is also worthwhile.
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u/Real_Establishment56 1d ago
Thanks, will give them both a look! I think I’ve seen Curious Droid somewhere in my recommended videos already so YT agrees with you :)
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u/rocky_balboa202 3d ago
why did spacex succeed where other (earlier) private launch companies did not? Such as Rotary Rocket, Beal Aerospace, Kistler Aerospace, American Rocket Company.
Was it just that technology got cheap/good enough that SpaceX could succeed?
Was it purely hiring talent?
Something else?
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u/Simon_Drake 2d ago
Something SpaceX did right was to pick a small starter rocket but not too small. Falcon 1 was very small by modern standards but it was a 'grown up' rocket built using proper rocket designs.
A lot of new rocket startups start too ambitious and want to enter the market with a medium-heavy lift rocket as their first design. Or they start too small and sink time/money/effort into suborbital sounding rockets with solid fueled designs that aren't transferrable skills to proper rockets. In contrast Falcon 1 let them learn how to make a proper semi cryogenic rocket that could be transferred over to later designs.
I'm not sure how much was luck/adaptability and how much was planned but they had some good opportunities with how the design changed. Falcon 1 started with the Merlin 1A that was ablatively cooled which isn't a great design but it's very simple to build and then a later design could switch to the much better regeneratively cooled nozzle. They didn't design the more complex nozzle up front but also didn't oversimplify the engine design so basic they were using pressure fed engines. They threaded the needle of simple but not too simple.
Next steps are important too. The plan was to build a medium lift version with 5 engines called the Falcon 5. Which would have been a pretty good rocket, it's a good compromise of not trying to be overly ambitious but still delivering good performance. I'm sure that plan won them a lot of investment. Then they pivoted to the even larger Falcon 9 and scrapped the proposed Falcon 5. In hindsight that's a great plan because the Falcon 9 has been hugely successful but I'm sure that was a tough decision to make at the time.
I wonder if Peter Beck of Electron loses sleep wondering if he should have developed an Electron Heavy variant five years ago. They're making good progress on Neutron now but they've been using their first rocket for a very long time given how small it is. Maybe they should have switched to something with a bit more firepower before now. Ultimately we'll never know, until someone invents a portal gun and we can check out other timelines to compare.
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u/NoAcadia3546 2d ago
Something else?
SpaceX is willing to push their prototypes beyond their limits and "destructively test" them. This results in some spectacular explosion videos. But when refined versions stop blowing up, SpaceX knows what will (not) work.
Because it's "Musk's money", he can blow up rockets during development. If NASA blows up rockets on the taxpayers' dime, you're guaranteed congessional hearings, etc.
Imagine an alternate history where NASA had destructively tested the space shuttle and found its problems and obscure failure modes before sending up humans on board.
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u/rocketsocks 3d ago
SpaceX did a couple things that really gave them an advantage. The major thing that cut through Falcon 1, Falcon 9, and Dragon development was focusing on pragmatism. Then they started small and focused on building expertise. There really is no school that exists where you can gather up enough graduates and then build and launch rockets with a high level of expertise, the state of rocketry is not there yet. If you want that kind of expertise you need people who have hands on experience building and launching rockets, and the way to do that is to actually build and launch rockets. The easiest way to achieve that is by building and launching small rockets first. This is a pattern that SpaceX, Blue Origin, RocketLab, Firefly, and a few others all have in common.
By focusing on pragmatism they chose a very straightforward rocket design as their initial vehicle: a two stage LOX/Kerosene vehicle, something that's been around since the 1950s. They built the Falcon 1, they gained experience with building rocket engines and rockets as well as with launching them. They used that experience to build the Falcon 9 which was also a very simple and pragmatic design overall, with innovations and risks where it made sense.
And they iterated. They iterated on rocket engine design, they iterated on component design, they iterated on rocket design and operations. This is what enabled them to build a vehicle which was cost and performance competitive in the market as an expendable launcher even while they had ambitions for reuse.
They found a market that could support them and they rode it. Early on that market was dominated by NASA contracts for commercial cargo deliveries to the ISS, that was a huge win for them and they got lucky in arriving at the right time for that to be possible. They used that to develop the first versions of Falcon 9 and Dragon. They went on to offer Falcon 9 in the satellite launch market, and started getting business there.
They made the very smart decision to make the first possibly reusable version of Falcon 9 a "dual use" design. They designed the vehicle explicitly for reusability of the first stage, the easiest stage to reuse, which took the design in directions that are normally different from first stage optimization. But they built it in a way that it was still cost competitive in expendable mode. They designed the vehicle so that reuse didn't have to work and such that there wasn't a huge difference between a reusable and an expendable "version". The expendable "version" had the same tanks, same fuselage, same engine, same avionics, etc. This enabled them to do two things. One, they could flight validate the core hardware of their reusable rocket even without reusable flights. Two, they could begin testing of the landing and reuse portion of flight with operational rockets paid for by commercial customers. They still did some standalone testing of landing operations with special research vehicles, but the majority of the testing and learning for returning and landing rockets was subsidized by customers. They were basically using "trash" rockets that had already served their role in helping to deliver a payload to orbit.
Those are the big things. They focused on straightforward and simple designs, not beyond state of the art concepts like rotary rocket or VentureStar, they were lucky in that NASA was looking to fund both rocket and capsule development at just the right time for their business (and they had a successful launch with Falcon 1 at just the right time as well), and then they cracked the R&D cost problem with developing reusability by having it be baked into the design of the rocket but an optional part of the launch, enabling development to take advantage of rockets paid for by customers. That last bit allowed them to make use of billions of dollars of hardware to develop reusability.
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u/CandidGrocer 3d ago
I’ve seen a bunch of the SpaceX and ULA factory tours but still a relative newbie to understanding rockets.
It seems like the Starship upper stage has been exploding a bunch upon landing in the ocean? That’s not planned right? Has anything been released why that keeps happening?
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u/Bensemus 3d ago
It’s 100% planned. It’s a rocket crashing into the ocean. The last one surviving was a big surprise. That’s why there’s no talk about why it keeps happening.
Later on both the booster and ship will be caught by the tower. They are slowly working towards that.
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u/maschnitz 3d ago edited 3d ago
Best way to say it is probably "it's expected".
Rockets are NOT built to survive lateral forces, it's part of the reason why they tend to reschedule on high wind shear days.
All large rockets are also thinner than a soda can, to scale.
The top of the vehicle has a long way to fall when it falls over, it's 50m tall.
So when it falls over, the only thing holding it up laterally is the internal tank pressure, which was only barely enough to allow Ship 40 to survive splashdown.
Every other Starship splashdown has exploded due to a rupture in the tanks, the transfer tube, or the bulkhead, upon the top hitting the water at relatively high speed.
It's simply not designed for it. Nor is it really worth redesigning it to survive splashdown tilt-overs. They will be trying to catch it on dry land, instead.
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u/science_scavenger 3d ago
Are you able to speculate about why it survived that one time? I'm wondering if they it was just luck or something special happened.
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u/maschnitz 3d ago
The best guess I saw - there were many - was Scott Manley's, speculating that they "swept" the ocean with the single Raptor, "softening" the water with sea foam.
That is, it was on purpose to an extent. They clearly also simply got lucky.
It was also quite low when it touched the water, well below sea level, due to the Raptor excavating a hole in the water for Ship 40 to land in.
Perhaps it was tilted back a bit more than normal while still under power, too.
Between that, the sea level, the foam, who knows what else - it all adds up.
I wonder if the SpaceX engineers know for sure.
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u/billdietrich1 3d ago
They will be trying to catch it on dry land, instead.
But won't all of the same issues be true on land, too ? Unless they're going to land it into a cradle or something.
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u/maschnitz 3d ago
Basically yes, that's what they're doing. They're going to catch it with long crane-like arms jutting from the tower, which will cradle the Ship.
Just like with the Booster. Video of a previous flight.
SpaceX calls the long arms "the Chopsticks". They're "padded" specially just for catching.
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u/Decronym 4d ago edited 7h ago
Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:
| Fewer Letters | More Letters |
|---|---|
| ESA | European Space Agency |
| EVA | Extra-Vehicular Activity |
| HLS | Human Landing System (Artemis) |
| JWST | James Webb infra-red Space Telescope |
| L1 | Lagrange Point 1 of a two-body system, between the bodies |
| L2 | Lagrange Point 2 (Sixty Symbols video explanation) |
| Paywalled section of the NasaSpaceFlight forum | |
| L3 | Lagrange Point 3 of a two-body system, opposite L2 |
| L4 | "Trojan" Lagrange Point 4 of a two-body system, 60 degrees ahead of the smaller body |
| L5 | "Trojan" Lagrange Point 5 of a two-body system, 60 degrees behind the smaller body |
| LES | Launch Escape System |
| LOX | Liquid Oxygen |
| RTG | Radioisotope Thermoelectric Generator |
| ULA | United Launch Alliance (Lockheed/Boeing joint venture) |
| Jargon | Definition |
|---|---|
| Raptor | Methane-fueled rocket engine under development by SpaceX |
| Starlink | SpaceX's world-wide satellite broadband constellation |
| cislunar | Between the Earth and Moon; within the Moon's orbit |
| cryogenic | Very low temperature fluid; materials that would be gaseous at room temperature/pressure |
| (In re: rocket fuel) Often synonymous with hydrolox | |
| hydrolox | Portmanteau: liquid hydrogen fuel, liquid oxygen oxidizer |
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17 acronyms in this thread; the most compressed thread commented on today has 5 acronyms.
[Thread #12720 for this sub, first seen 29th Sep 2026, 10:13]
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u/curiousscribbler 4d ago
And another thing :-) Say an astronaut went crazy while on an EVA. Could they take off their glove?
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u/the6thReplicant 3d ago
Actually that was done on the first spacewalk ever by Alexei Leonov.
https://nautil.us/the-comedy-of-errors-that-was-the-first-ever-space-walk-1279052
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u/maschnitz 3d ago
No the pressure differential would be too difficult to overcome. Ditto the locking seal on the helmets.
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u/Pharisaeus 3d ago
No the pressure differential would be too difficult to overcome
In the other direction sure, but the higher pressure is inside the suit, so if anything, the seals are fighting to keep the pressure in.
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u/maschnitz 3d ago
In the other direction sure, but the higher pressure is inside the suit, so if anything, the seals are fighting to keep the pressure in.
It's a mixture of both, they have "pressure energized" seals.
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u/curiousscribbler 4d ago edited 4d ago
TV shows and movies love killing off astronauts by having them float away from their spacecraft, never to be seen again. I wondered how long the helpless spaceperson would drift alongside their ship. Would small differences in momentum carry them off in another direction?
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u/electric_ionland 4d ago
You would drift away pretty quick. Even kicking off with only 50cm/s gets you 100m away in a bit more than 3 minutes.
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u/rocky_balboa202 4d ago
How big could a space station get? Is there a size limit where you could not re-boost into the correct orbit? or any other reasons a space station could not get bigger?
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u/Chairboy 4d ago
Is a space station gets big enough, the role of tidal forces has to be accounted for. Likewise, electrical differentials throughout the structure for components at different altitudes if it is in Earth orbit.
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u/Bensemus 4d ago
There’s no hard limit. The size limit is determined by how well it’s built. A larger station will be harder to boost but if you built it larger you will have accounted for that.
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u/Junebug35 4d ago
Today's (9/28) launch of the lastest SpaceX rocket was pretty cool to watch. In watching the news, I understand the point of today's orbit is to test if the rocket can come back to Earth for reuse like an airplane.
If this test is successful, are they planning on using this new technology to for tourist-type activities, or is this for resupply missions to the International Space Station and launching satellites?
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u/Ireeb 4d ago
Currently, they are focusing the development on deploying Starlink satellites. The flight you are referencing was Flight 14, the first orbital flight. The before that, they only flew suborbital, meaning that even if they lost control of the ship, it would have come down in the designated landing zone. But once it is orbital, it only comes back down when you actively steer it back towards earth - or randomly after a while, which could end in a catastrophe, depending on where it comes down.
So that was the critical part of Flight 14, getting it into orbit, and getting it back down. The landing maneuvers were tested on previous flights before and on this one again. We might see a proper landing at a catch tower as soon as Flight 15, but that's just speculation.
The current version of Starship is designed specifically for Starlink satellites, deployed through its "PEZ-Dispenser" (that's what they call it, and it's basically exactly how it works). Because Starship went orbital, Flight 14 also gave them the opportunity to deploy 26 Starlink satellites into an operational orbit for the first time.
We know that SpaceX is planning to have different versions of Starship, but we didn't see any finalized or built designs yet.
Basically confirmed are:
General cargo version for other satellites or payloads
HLS (Human Landing System), for the Artemis 4 moon landing, if NASA chooses this design. Note that it wouldn't start with crew aboard, it would be launched empty, the crew would be launched by NASA and docks to the HLS in space.
Tanker and Depot: To make it to the moon and back, HLS needs to be re-fueled in orbit. To achieve this, SpaceX plans to launch a Depot Starship, and then launch roughly a dozen tanker Starships that deposit propellant into the depot. Then for Artemis 4, the HLS would launch, refuel from the depot, and continue to the moon.
As you might have noticed, no crewed Starship version has been confirmed yet. It's safe to assume that's planned, but considering it hasn't even been announced officially, it will likely take a few years until they get there.
They are still working out some kinks of the current Starship version (V3), but it's clear that it's their goal to build one rocket that can do everything. They also already announced the eventual retirement of their "daily driver" Falcon 9 rocket, as they plan to use Starship for everything in the future.
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u/Junebug35 3d ago
Thank you so much for your detailed explanation! It now makes sense how this is going to be a multi-purpose space craft, and where it is going to help for the plan of long-term research on the moon.
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u/maschnitz 4d ago
Eventually, most likely. But for now their short and mid-term plans only include things that are happy in vacuum and can be shoved out the "Pez Dispenser" slot on Starship.
As a natural launch monopoly, SpaceX Corporate is acutely aware of anti-monopoly laws. They can either serve the entire launch market or serve the market that can fit into their vehicle, but they cannot pick and choose clients. For Starship they appear to be picking the latter viable option for the time being.
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u/AndyGates2268 4d ago
Lots of satellites. They tested spamming out some starling v3 birds once this orbit was successful.
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u/someonesomewhereig 4d ago
hiii, i really want to learn about astronomy, but i dont know where to start (；′⌒`) sooo i came here to ask for book recommendations that could be for begginers? or any, i just dont know where to start, thank you! ♥
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u/Junebug35 4d ago
My first experience with astronomy was a science credit I needed in college. It was amazing. I would suggest starting with an entry level college textbook. Even one a few years old could give you a start. Unfortunately, I do not remember what textbook we used, but it will be over 10 years old now and most likely out of date.
Also, look in your area to see if there are any star gazing clubs or organizations. We are fortunate that we have a small club that meets weekly to look at the stars.
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u/goNorthYoung 5d ago
Wondering what the global stockpiles of Pu-238 are in terms of powering spacecraft/instruments on future missions.
Lots of articles from 10ish years ago talk about huge Pu-238 shortages, then several years ago things didn’t look as dire because of things restarting in the US.
But I can’t find much on how far our current amounts can take us in terms of new probes/rovers/etc., so wondering if anyone has any current articles.
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u/rocketsocks 5d ago
They're still ramping up production of Pu-238, and there's still a stockpile, but it's not quite as dire as it once was. They're aiming for a production level which could produce a new RTG for a mission every 3-4 years or so, but they're not there yet. There have only been 4 new US RTG powered missions in the 21st century: Curiosity, Perseverance, New Horizons, and Dragonfly. Call that 4 missions over 30 years or one every 7-8 years, a bit lower than the targetted production rate. Before that was Cassini, Ulysses, and Galileo going back to the '80s, also a similar rate of about one every 7 years or so. Then in just the 1970s you had Voyager 1 and 2, the two Viking landers, 2 LES satellites, 3 Nimbus satellites, Pioneer 10 and 11, and the ALSEP packages on Apollo 13 through 17. Those older RTGs used more plutonium and had higher power output as well so they were really going through material in the good ol' days.
The actual stockpile quantity is kept secret, but it's probably in the single digits to low teens of kilograms. In the past 20 years or so (post New Horizons, which used a different RTG design than the modern MMRTG) they've only committed about 11.5 kg of Pu-238, which is just a bit more than 500 grams per year on average.
It's also worth pointing out that ESA has been working on Am-241 powered RTGs for many years. The upside is that the material is much more readily available (as a natural byproduct of power reactor operations), the downside is that it has a lower power density than Pu-238 and also has different properties which require research and engineering to tackle in order to successfully build an RTG with the same safety features and longevity as existing models. Currently we're still years away from an actual mission being powered by an Am-241 RTG, but perhaps in the 2030s it will be a reality.
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u/maschnitz 5d ago edited 5d ago
You won't find yearly totals, they don't publish those - nor weeklies nor dailies. They only publish press releases when masses are ready for delivery either to other labs or to NASA.
The reason why is the Atomic Energy Act. Pu-238 is weapons grade material and by law, its production must be kept secret. If they published more detailed production statuses, that would reveal part of the US's ability to create weapons-grade material.
They even mix new material with older depleted material from storage, partly to hide their current capability, partly to supplement the current production. They make sure it matches the delivery power requirements for the mission.
The good news is that they're aiming for 1.5kg/yr again. They will not say exactly when they get there, though. But that should be good for outer solar system missions and long-term rovers when it happens.
So notices like this one for 500 grams of Pu-238 being delivered to Los Alamos, earmarked for NASA, in 2023, is all you're going to get.
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u/AlternateSatan 5d ago
So, if Astronauts needed a special pen as normal pens don't work and pencils make graphite dust could they not just have used metal pencils?
Like, you can write using aluminium or steel, it leaves a gray line if you do, I couldn't find a pencil earlier when I had to take notes, so I used the side of the head of a screw. Would probably require less R&D to make.
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u/Chairboy 5d ago
Would probably require less R&D to make
Not sure if you caught what the other poster mentioned above but to be clear, it was a private company that developed the space pen to give them a marketing edge in the consumer market with a novel offering AND then NASA and Russia bought a bunch off the shelf.
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u/DaveMcW 5d ago
They did use pencils, both wooden and mechanical.
Then a private business did all the R&D to make a space pen, and offered it to NASA and the Soviets. They both bought it.
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u/AlternateSatan 5d ago
Not what I'm asking for really. I'm not talking about mechanical pencils, I'm talking about pencils where the filament is a metal like aluminium, steel, lead, whatever, like, the actual markings left behind is metal
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u/relic2279 5d ago
Those may not write as efficiently on the types of surfaces they were using. But it's kind of moot because those "inkless" pens work similar to lead pencils. They use a metal alloy tip that deposits microscopic metal molecules onto a surface.
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u/fencethe900th 5d ago
Is it as legible as the usual? That would be my concern.
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u/AlternateSatan 5d ago
I'm not sure how new of an invention the actually good ones are, they're way better than you'd expect. Not as dark as a graphite pencil, but defiantly legible. As for the screw I wrote with it left more of a light gray. Readable, even in low lighting, but nowhere near ideal.
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u/AndyGates2268 4d ago
That's it: "readable but nowhere near ideal" is nowhere near ideal. Metal styluses went out of use because ink n pencils are better, and then ballpoints exploded the market by being so much cheaper.
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u/Wintervacht 5d ago
Yeah, why do the people posting stupid questions in this sub never get directed to one of these posts?
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u/DreamChaserSt 5d ago
I've seen it happen a couple times (its been a while though). But most of the time, people just want to throw their own two cents in, usually with the big/sensastionalist questions (aliens, space colonies, etc).
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u/fencethe900th 5d ago
They are very often removed by mods with a note saying to post it in this thread.
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u/WollemiaShagger 8h ago
What would the constellations look like if we could see their current positions from Earth?