RyanRising

thanks johnnyothan! this is a lot of fun to play with and as a mod it's come so much farther and gotten so much more polished than I could have imagined it would be. It must be an incredible amount of work to make this happen.

I think those are roll control thrusters! Yep! Saturn’s S-IVB was a notable use of internal insulation, so it’s definitely doable.

I'm not sure that's plausible. For one, we can see that in the pic they showed of a WDR that there isn't ice on the tank when that happens with things much less cold than liquid hydrogen on uninsulated tanks. Secondly, because of its unique properties - not just freezing water but often liquefying air through a tank wall if not insulated - I don't believe even for short hops or static fires that the boiloff losses would be negligible. Even with insulated tanks, remember that some hydrogen rockets have pour twice their fuel capacity into a tank before it fills.

I wonder how they're handling insulation. It must be inside the outer shell because we can see bare steel there, so something similar to S-IVB maybe?

The approach outlined here seems to be lacking a temperature-dependent heat generation or rejection property? Without that feedback, won’t systems either cool to the temperature of their environment, heat until something explodes, or remain constant at whatever temperature they happen to be? This is fine if that temperature happens to be what you want to operate at, but if parts are to have different behaviour based on their temp doesn’t the lack of any feedback loops make getting a part to a desired temperature frustrating at best?

Kinda contrary to what Pthigrivi said, I think big investors have shown pretty well that they're not necessarily the smartest people around, and are very impressionable. If that "big vision" is persuasive enough, you can get people to funnel money into it without necessarily having a clear path to profitability. At any rate, SpaceX's Mars plans seem to be more aligned with stroking Musk's ego rather than making technologies for a practical mission architecture. The really important, development-heavy parts of a Mars mission: "how do we keep people alive and healthy for so long in such unforgiving environments," "what can we do there to best make use of human presence," while extremely criticial, aren't sexy. Making the biggest rocket ever made? That's sexy, put our money and effort into that. The payloads aren't just going to magically be there to launch once Starship starts working, but what plans SpaceX has put out almost unviversally glosses over that part, instead focusing on the evocative images of domes already there, big towers touching down on the red planet, people stepping out from the lander in a SpaceX Dragon IVA suit, etc. It's not serious as a Mars plan, but what it does do is make the people who are putting money into it - one person in particular, but no doubt the others too - think they're contributing to some great higher purpose, and feel motivated to continue fudning the project. In the meantime, they're making a really big rocket that has the potential to be very useful in a much more general sense, so that's cool and I'm rooting for them there. But when they say "making humanity multiplanetary," given the information of what they're actually doing, it reads to me as either very naive about what really needs doing, or just a platitude to tell those with infludence "hey that money is definitely well spent here, don't take it elsewhere."

Yeah, that's the reason given. I guess it's less work to make a shorter one? I don't imagine material costs factor in all that much.

Nope, evidently not.

I guess I should have picked up on the double-walled tank during the EDA tour, but that's a neat way to demonstrate its presence.

It is true that I’m making several assumptions about “what the typical LEO entry is.” Those assumptions are relatively high altitude, >~30km, and speeds of less than 8 km/s. Anything above those speeds wouldn’t be a low earth orbit and anything reaching those speeds at lower altitudes is… well it isn’t a crewed spacecraft like any we’ve seen before. I think these are reasonable assumptions. The paper you reference does not support your claim that LEO entires are dominated by radiative heating at first and then convective heating as they slow down. It does show that this is the case for higher-velocity entires, and the paper is clearly concerned more with those than LEO ones. These graphs start from 10 km/s and only go up from there. However, even in the larger 5m radius case the heat fluxes at 10 km/s are roughly equal, and it’s reasonable to extrapolate that it becomes very much lower at LEO entry speeds of 8km/s. (edit: to be clear, this doesn’t mean there is no radiative heating whatsoever in these regimes, only that it is significantly lower i than the convective heating) The equations you show are proportional, and describe the growth of each. However, this still leaves room for constant scale factors, and the examples they give show that for the size of entry vehicle they consider, those scale factors work out so that convective heating will dominate radiative heating at lower entry speeds near 8 km/s. The presentation says as much: reflective TPS is applicable for high-velocity, interplanetary missions. It doesn’t claim it’s very useful for LEO missions. The scales that this presentation considers include crewed space capsules that have been fielded. For those, it’s pretty clear that convective heating is higher than radiative at speeds < 8 km/s. However, it’s still possible that the flatter areas of the Space Shuttle experienced much more significant radiative than convective heating. I don’t have data on the type of heat flux experienced in those areas, but maybe I just need to look a little more.

Radiative heat transfer from the vehicle is indeed very significant during shallow entries, though. That is indeed why the high-temp shuttle tiles were black, and wouldn’t have worked well at all if the majority of the heat coming into them was radiative.

I think you’ve got things mixed around. It’s worth noting that while you see silver reflective back shells on Orion and Apollo, you do not see those on LEO spacecraft, which should tell you about the different types of heating they experience. But if we just make numbers up and only look ant the visible features of spacecraft, even if we do math on those made-up numbers, we’d be here all day. Instead, let’s look at some actual material on the topic. Here’s what Mr. H. Julian Allen of NASA Ames has to say about the topic: on ballistic missiles entering from near-orbital velocity: Of manned space vehicles at orbital velocity: This implies that convective effects make up a significant amount of the heat transfer for atmospheric entry vehicles. However, what really seals the deal is this little transition: He outright says that the heating is still essentially convective at speeds even exceeding that of LEO. At this point, the Mercury orbital flights had already been performed, so if NASA had designed its TPS, and that of Gemini, assuming this to be true when in reality radiative heating dominated the entry environment, they would have cooked their astronauts. Mr. Allen then goes on to describe the radiative heating effects that occur with the higher-energy plasmas associated with super orbital velocities, and yes, this was clearly important enough that a reflective backshell had to be incorporated onto Apollo where the previous spacecrafts‘ leeward sides were designed to essentially be black bodies. https://ntrs.nasa.gov/api/citations/19640013352/downloads/19640013352.pdf And from another report, https://ntrs.nasa.gov/api/citations/19980227977/downloads/19980227977.pdf, here’s a handy graph (though in imperial units, bleh) of the rough relationship of convective and radiative heating. As you can see, in the regime of typical LEO spacecraft entries the convective heating is greater than the radiative by some orders of magnitude.

Now, they can’t possibly think Artemis III can still happen in 2025. That was earlier predicted in a timeline that also had starship launching its orbital test flight in early 2022. But since the people putting together those schedules should know that better than anyone, why put this out? Maybe they were moving stuff over to make room for it but ran out of time before they could slide Artemis iii to the right.

those are almost completely separate issues, aren't they? Feels like the decaying orbit is a red herring here.

I appreciate the post, as much as it seems like damage control. I’m very disappointed to hear there are issues with scaling the fuel flow, however. This was a known and problematic issue with large scale crafts in KSP1, and I would have expected the development of KSP2’s system to specifically avoid that, since very large crafts are supposed to be common in this game. but, whatever. I’m not gonna fix it by complaining. I hope you guys can work that out satisfactorily, and if you do I’ll be happy to buy the game.