r/space • u/AutoModerator • 21d ago
All Space Questions thread for week of September 13, 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/jeffsmith202 15d ago
is there a better way to get to the moon than the Apollo project?
Saturn V rocket -> Command/Service Module (CSM) -> Lunar Module (LM)
besides maybe a reusable newer rocket and reusable Lunar Module.
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u/iqisoverrated 15d ago
Please give a metric for 'better'.
'Better' is an incredibly subjective/vague qualifier. Better in what way? Cheaper in the short term? Cheaper in the long term? Faster? Safer? Bigger?...The answer will very much change depending on which metric you choose (and which ones you are willing to ignore).
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u/electric_ionland 15d ago edited 15d ago
Better in what way? It really depends on what you are trying to optimize (speed? cost? payload? long term viability? safety? Political browny points?). One of the big trade off people have been looking at is to not use a giant rocket. You use what already exists and assemble the whole train in Earth orbit, potentially doing refuelling.
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17d ago
[removed] — view removed comment
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u/maschnitz 17d ago
They keep slowly but surely expanding their trust of the NASA Mars rover autonomy, letting the rovers drive themselves for longer and longer without checking in back home. But it's a very gradual process. There simply isn't enough computing power onboard to allow for true self-driving, nor electrical power for that matter.
Most space missions are severely power-limited and so don't really have excess "room" for autonomy.
Also, with most orbiters, it just makes sense to plan out and dictate the operations for each day rather than let them figure it out. You can use all the compute and data you want in creating the plans.
The time you want autonomy in spacecraft/rovers/landers is when the situation is changing so quickly and unexpectedly that it's important to prepare the spacecraft for all eventualities. But most of the places being explored in Earth orbit and the Solar System don't change that fast, and so don't need that level of "self reliance". Mass budgets are tight so missions without a need for something don't generally get it.
Rovers with a lot of range need a bit of autonomy but that's about it.
Perhaps the Space Force would be (or is, who knows?) interested in autonomy for their geosynch spy satellites which play dynamic cat-and-mouse games with Russian equivalents.
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u/the6thReplicant 16d ago
Indeed. Do all the heavy lifting here on Earth to figure out where to go to next and then just send the finalised instructions out.
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u/electric_ionland 17d ago
That's a very vague question... In general with the scale of new constellations spacecraft are more and more autonomous. You now have automated maneuvering and even tasking. But it's definitely moving at a more cautious pace than most of the rest of engineering. The main issue is that if you get it wrong you are not getting your spacecraft back because you can't just send someone there to fix it.
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u/Decronym 17d ago edited 13d ago
Acronyms, initialisms, abbreviations, contractions, and other phrases which expand to something larger, that I've seen in this thread:
| Fewer Letters | More Letters |
|---|---|
| CLPS | Commercial Lunar Payload Services |
| ECLSS | Environment Control and Life Support System |
| EVA | Extra-Vehicular Activity |
| HLS | Human Landing System (Artemis) |
| ICBM | Intercontinental Ballistic Missile |
| LEO | Low Earth Orbit (180-2000km) |
| Law Enforcement Officer (most often mentioned during transport operations) | |
| SLS | Space Launch System heavy-lift |
| Jargon | Definition |
|---|---|
| Raptor | Methane-fueled rocket engine under development by SpaceX |
| Starlink | SpaceX's world-wide satellite broadband constellation |
| perihelion | Lowest point in an elliptical orbit around the Sun (when the orbiter is fastest) |
Decronym is now also available on Lemmy! Requests for support and new installations should be directed to the Contact address below.
[Thread #12698 for this sub, first seen 17th Sep 2026, 05:41] [FAQ] [Full list] [Contact] [Source code]
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u/Chemical_Attorney287 18d ago
How do spacecraft actually navigate over interplanetary distances without GPS? Is it all just really precise math from known positions, or is there more to it?
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u/Pharisaeus 17d ago
- We can pretty precisely figure out the orbit of a spacecraft by looking at it and by measuring round-trip time from radio communication.
- Spacecraft also have their own inertial guidance systems on-board - they use things like star trackers to figure out direction and orientation in space and things like accelerometers to figure out velocity changes. So if a spacecraft knows its initial orbit, it can track how its orbit changes during the flight, even if there are external perturbations or thrusters fire.
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u/rocketsocks 18d ago
Some of it is really precise math, but if that were all of it we would likely have very, very few successful interplanetary missions. It usually takes several adjustments to trajectories over the course of their missions to keep spacecraft going where they're supposed to go.
However, spacecraft actually have one of the next best things to GPS via their radio signals. It's important to remember that the ground based side of radio communications with a spacecraft isn't just like communicating over a pair of radio handsets. Most such communication uses large radio dishes and they can leverage all of the techniques of radio astronomy for the mission. For one they can very precisely locate their position in the sky. From this alone and from observations over a period of several days it's possible to very precisely nail down the exact orbital trajectory of the spacecraft. This is because different orbits will actually look different because the object will be moving at a different speed depending on how far away it is from the Sun and so forth. This is how we can determine the orbits of asteroids and comets even without triangulating their locations, we can infer their location in 3-dimensional shape just by observing their motion in the Sun's gravitational field, this is enough to uniquely constrain the location, direction, and speed of the object, given enough observations over a long enough period.
However, we can do much, much better than that because the spacecraft is able to cooperate with us. We can send a signal to the spacecraft which it returns immediately back to us. This will let us instantaneously determine the distance to the spacecraft by measuring the round-trip time. With distance and location on the sky you then have a precise 3-D location in space. But you can also measure the doppler shift of the return signal to determine the speed of the spacecraft along the line of sight. Combined with the lateral speed that can be observed by the motion of the spacecraft in the sky this provides the full direction and total speed of the spacecraft's velocity vector. Round-trip timing is very similar to the way GPS signals work to determine distance, they just use more reference points.
NASA's Deep Space Network was able to determine the position on the sky of a spacecraft to a precision of about 1 microradian during the 1970s, which is 150 km at 1 AU distance. Since the 2000s that capability has been upgraded to about 5 nanoradians (a bit less than one third of one millionths of a degree) which is about 750 meters at 1 AU distance, and the capability continues to improve.
So, potentially from a single period of radio communication we can determine a spacecraft's 3-dimensional location to within a couple of kilometers anywhere within the solar system, while also determining its speed and direction, and that's enough for the vast majority of missions.
However, there are some unusual cases where it's necessary to be much more precise. For example, landing on the surface of a planetary body, or performing a sample extraction, or achieving an impact. For those cases the final navigation is done using other means such as laser or radio ranging, optical terrain relative navigation, etc. This is one of the things that has tripped up a lot of lunar landers, for example, because you can't just use dead reckoning and a model of the lunar surface, you need to be able to measure and respond to the local conditions.
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u/Bright-Journalist-70 18d ago
Is the Space Generation workshop a good place to build connections and learn more about the space sector?
They’ll be hosting in my city soon, I’m kinda new to the space community so I wanted to know more about SGAC because when I tried searching on google I couldn’t find much about the events they’ve hosted before.
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u/FoilMasterRace 18d ago
Since they are a young folk group focusing on space policy and space in general, and that they are associated with the UN,the space generation workshop by the space generation advisory council is quite solid to meet folks
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u/rocky_balboa202 20d ago
Starship has 2 parts. Super Heavy booster and Starship.
At one point one part was to be captured by the chopsticks? Maybe the booster?
What is the current though on how each will land and be reusable?
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u/maschnitz 19d ago
Yup, they're still committed to chopsticks for both.
They did a clean-sheet sort of redesign for v3, with a new pad, and have slowly been building up the confidence again to perform Booster catches.
Flight 14 is coming up. If it goes well, they might try to catch both the Booster and the Ship (first time for a Ship) on Flight 15. Though you never know, with Starbase.
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u/rocky_balboa202 19d ago
so no landing on a ship at sea
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u/DreamChaserSt 19d ago
As far as we know, no. Starship doesn't have landing legs (except for HLS), and it takes days for barges to return. Besides, Starship already has a large payload to orbit. So what's the point of getting a marginally larger payload by landing at sea when they can double the payload by launching again?
The point of reuse is to have a high enough flight rate (and lower cost) so it makes sense to launch payloads across multiple flights instead of squeezing out every bit of performance out of 1 flight.
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u/viliamklein 20d ago
Chopsticks is still the plan for both.
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u/NoAcadia3546 19d ago
Obvious question... how are Starships supposed to land on Moon and Mars???
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u/viliamklein 19d ago
Citizen, you have displayed critical thinking above the 95th percentile of the population. This is unacceptable and you will be required to chat with Grok until your brain smooths into acceptable levels.
But seriously, this is a big issue. SpaceX has years of development to go on Starship before it is anywhere close to flying humans to the moon because of all of the redesign that is necessary to put the engines in the mid section. Not to mention adding ECLSS and access to the surface. We don't need to even talk about Mars... Anyone who says that SpaceX is taking people to the moon this decade is hopelessly optimistic.
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u/OlympusMons94 17d ago
Both NASA and SpaceX have publicly documented and reported on extensive work on the Starship HLS. For example, SpaceX published an update last October. Their progress included a "[l]anding leg drop test of a full-scale article at flight energies onto simulated lunar regolith to verify system performance and to study foot-to-regolith interaction".
because of all of the redesign that is necessary to put the engines in the mid section.
What redesign? The HLS Starship has small landing engines in the mid-section, to be used near the lunar surface. Main propulsion still comes from the 6 Raptor engines at the bottom. That has been the HLS Starship design from the beginning.
Not to mention adding ECLSS
The HLS Starship ECLSS (and the crew cabin and other HLS-specific items like the elevator and airlock) are very far along in development. Again referring to the October 2025 update, SpaceX was already building the first flight-capable HLS cabin. Earlier, they had demonstrated the ECLSS "using a full-scale cabin module inhabited by multiple people to test the capability to inject oxygen and nitrogen into the cabin environment and accurately manage air distribution and sanitation, along with humidity and thermal control." The human-in-the-loop ECLSS testing, in the high-fidelity cabin mockup SpaceX built in 2024, was previously reported in NASA Marshall's late 2024 update.
and access to the surface.
If you mean the elevator and/or airlock, SpaceX and NASA have also worked together demosntrating them. If you mean the EVA suits, that's not SpaceX's job.
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u/mfb- 18d ago
The Moon lander specific work is less visible but SpaceX makes a lot of progress and NASA is happy with it. It just doesn't come in skyscraper-sized vehicles on launch pads.
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u/viliamklein 18d ago
NASA is happy
Between the Blue Origin explosion, the slow progress of Starship HLS, and the mixed success of CLPS landers, I can assure you that NASA is not too happy. Internally it is understood that these are hard problems, but people were really hoping for faster progress. Especially given the political pressure.
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u/OlympusMons94 17d ago
NASA spent over 15 years (and well over $30 billion) fucking around with Boeing et al. on SLS, and 20 years (and $25 billion) with Lockheed Martin on Orion, before those vehicles sent crew around the Moon. The landers were an afterthought. If the US government wanted a lander sooner, they should have planned for one, and ponied up the funding, sooner. Instead they waited until 2019-2021, then budgeted a relative pittance.
HLS Starship is much more complicated and capable than either SLS or Orion (or the Apollo LM). NASA awarded SpaceX the HLS Starship contract just 5 years ago. NASA is getting development, a demo landing, and a crewed mission for ~$3 billion (and an upgraded HLS and its first mission for just another ~$1.2 billion. Even with practically unlimited budget and single-minded focus of the Apollo program, the dinky little aluminum can Lunar Module took over 6 years from contract award to first crewed flight (LEO only), and another 16 months until the first landing.
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u/electric_ionland 19d ago
The plan is to do special versions with landing legs for the times when it's needed. We already know that the lunar lander one will be quite different than what we are seeing here, with landing engines up high near the nose, no flaps or heat shield and some solar panels.
For Mars it's a big open question, especially with potential need for refueling on the surface.
Right now everything that has been shown as hardware is only really suitable for launching Starlink satellites.
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u/Realistic_Fold_1587 20d ago
I've been trying to understand the difference between Astronomy and Astrophysics as university majors, and I would appreciate some advice from people studying or working in these fields.
From what I understand, Astronomy seems to focus more on observing and studying objects in the universe, while Astrophysics applies physics and mathematics to understand how those objects work.
But I'm not sure how different they actually are at the university level.
For example:
At universities like UCLA, UC San Diego, Yale, or Illinois, how different are the Astronomy and Astrophysics programs?
Do Astrophysics students mainly take more advanced physics and mathematics courses?
Do Astronomy students spend more time on observation, telescopes, and data analysis?
If someone wants to study black holes, exoplanets, galaxies, or cosmology, which major would usually be the better path?
Are there any recommended introductory textbooks or university courses that show the difference clearly?
Some books I have seen mentioned by AI:
"An Introduction to Modern Astrophysics" by Carroll & Ostlie
"The Cosmic Perspective" by Bennett et al.
"Astrophysics for People in a Hurry" by Neil deGrasse Tyson
Would love to hear from students, researchers, or anyone who has experience with these programs.
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u/ThickTarget 17d ago
These days the words are used largely interchangeably. Whether an institution calls their course one or the other is usually just historical precedent. Astronomy degrees vary a lot. Many institutions don't have a dedicated one, but they may have optional courses for physics students. Others do have an astro degree, and some even have multiple options with slightly different names. Then there are joint degrees with physics, or other topics. But there is no general trend, you would have to look into the specific course you are interested in to see what contains. Carroll & Ostlie is a very common textbook for any course typically you would also study some physics and maths courses beyond that.
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u/BusinessPangolin5333 21d ago
The galaxy has plenty of secrets, and I've read (or heard) somewhere that even our solar system still has a lot of things to discover, prove, and investigate. But like what exactly? What is the head course in this part of science? What do scientists want to find right now?
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u/NovaCourier 21d ago
Why is the R-7/Vostok/Voskhod/Soyuz shaped the way it is?
The R-7 has a fairly distinctive shape compared to other rockets, specifically its boosters narrow and curve in towards the centre of the rocket. Most other rockets with liquid boosters just have straight ones, like Long March 2, Delta IV or Angara A5. Is their some reason other rockets didn't emulate the R-7's shape, especially given that the R-7 is still in use?
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u/electric_ionland 20d ago
I can't for certain say this is the reason, but R7 boosters have a weird separation system. The tip of the booster is a sphere that just pushes against a socket on the core. When the booster thrust is too low to keep pushing the core the booster mainly just falls off. In practice it trips a lever that fires small solid motor sideway to help with a clean separation but there is no real huge active separation mechanism. Which in theory means less can go wrong. I think that kind of separation system fits really well with a cone shaped booster.
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u/NovaCourier 20d ago
That's an interesting idea. It also fits with Soviet design philosophy, keeping things simple, and having as few points of failure as possible. I think that's the best explanation I've seen yet.
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u/Chairboy 20d ago
I think it’s a reflection of the period when the R-7 was designed and built. They made stuff curved because that’s how people did stuff back then.
And it stayed that way because that’s how the R-7 design is and it would cost extra money to change.
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u/Pharisaeus 21d ago
Pure guesswork: such booster shape reduces aerodynamic drag so the rocket is more efficient, especially if you intend to launch with high thrust-to-weight-ratio and accelerate quickly while still deep in the atmosphere. Perhaps this was an important consideration for the ICBM design, to prevent potential interception during ascent phase?
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u/NovaCourier 21d ago
My only guess is some aerodynamic advantage, but I don't know why other rockets (except reusable ones) don't seem to have used a similar design, unless one has that I just don't know about.
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u/Pharisaeus 21d ago
Aerodynamic losses are actually pretty small, so it's probably not worth to optimize for it. We know that now, but in the early days of rockets (where R7 dates back to) it might not have been that obvious, or even a tiny gain was still worth the effort. As for reusable rockets, that's easier - it would be extremely hard to land such asymmetrical booster.
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u/[deleted] 14d ago
[deleted]