sevenperforce

Current progress:

I'm looking closely at the LOK-LK design and apparently there was a telescoping boom that the cosmonaut would ride from the orbital module on the LOK down to the access hatch on the LK. I haven't been able to find any photos or diagrams or drawings of it, though. Anyone else come up with anything?

This sounds like a stage, at least how a stage is defined in KSP. And that is exactly what I meant. Eh, you're right, that's probably just semantics. I was thinking of it more like a fairing -- structural hardware jettisoned when no longer used. I don't call Falcon 9 a "three stage rocket" on account of its fairing. Hot staging describes the upper stage being fired to assist with separation, regardless of whether the lower stage is still burning or not. I believe the Proton's second stage fires after the first stage starts to shut down, while the Soyuz upper stage fires two seconds before the core begins shutdown. Both are considered hot staging. Pretty much anything that does not use dedicated separation motors (or, in the case of Falcon 9, a dedicated pusher rod to shove the upper stage away from the interstage) is hot-staged. I would say that hot staging is any system where the upper stage engine thrust provides the impulse to physically separate the two stages. Anyway. I was going off of memory when I wrote my earlier comment and I must correct myself: the crasher stage was jettisoned at 1-2 km, not a few hundred meters above the surface. Another cool fact: the LK used four "settling motors", weak solid rockets that fired on contact with the lunar surface in order to prevent it from bouncing or tipping if it landed on a hillside. These are really cool photos: The center engine was able to throttle down to 41% for the hover and landing. The two nozzles on either side are tied to a single turbopump and provide backup/abort. The four nozzles around it are exhaust nozzles from the turbopumps; they provided differential thrust for pointing and fed from either turbopump. The center engine had two clamshells that closed over it on touchdown to prevent debris impingement. Both turbopumps ignited on liftoff from the lunar surface, and once thrust was verified, the backup was shut down. If there was a thrust shortfall on the center engine, then it would shut down and the LK would proceed to lunar orbit using the backup engine/nozzles.

You can use a gravity assist off a planet or moon to correct your inclination relative to that planet or moon, but you cannot use a gravity assist off a planet or moon to circularize to a closer orbit. You have to use a different body. If you have two bodies close together, you’re in luck because you can build up assists between them to go to a third destination. For example you can go Kerbin - Eve - Kerbin - Eve - Kerbin to get a very cheap trajectory to literally anywhere. But unless there are multiple bodies so you can use gravity assists at your destination (e.g. Jool) then you still have to either aerobrake or brake propulsively. Gravity assists bend your trajectory. For example, it’s cheaper to go from Eve to Kerbin than from Eve to Moho. So you could burn out of Eve’s SOI from Gilly, wait a year, and get a very close hyperbolic pass to Eve for maximum Oberth effect so a very small burn will kick you up to Kerbin. Use a reverse gravity assist off Kerbin to lower your Kerbol periapsis to cross below Moho’s orbit, and then use a gravity assist off Eve to raise your periapsis to match Moho and lower your apoapsis to match Eve. You can then use Moho to correct your inclination over a few orbits before you burn for capture. But that capture burn will never be less than 2300 m/s.

Ah, dammit, you're right. I just took a quick look and you only need 315 m/s to leave Moho's SOI. However, you still need 2287 m/s to reach an Eve-crossing orbit, so even if you can use all manner of gravity assists to correct inclination, your minimum braking dV from hyperbolic Moho entry to landing is going to be 3157 m/s. No possible gravity assists can get you to have a Kerbol apoapsis lower than the orbital altitude of Eve.

It makes orbit with some fairly straightforward flying… Not really too much work. I have about 40 or 50 m/s of margin after deorbit. However, I keep having trouble with entry. That single fin really, really wants to burn up.That single fin really, really wants to burn up.

To get off Gilly and leave its sphere of influence, entering Eve’s orbit, will cost you a minimum of 440 m/s. It will cost more to burn out of Eve’s SOI, although not very much. You can then use a series of gravity assists off Eve to lower your Kerbol periapsis until it crosses Moho and get the correct inclination. However, Moho has no atmosphere. Accordingly, you will have to brake into low Moho orbit propulsively. Even if you could somehow use gravity assists to enter a Kerbol orbit exactly matching Moho’s (which is not possible) it would still cost you a minimum of 2400 m/s to get from even the lowest-energy hyperbolic orbit into a low circular orbit. It will then cost another 870 m/s to deorbit and land. So those are the minimum energy requirements. And that is not even counting the reserves you need to get out of Eve‘s sphere of influence, or to complete your gravity assists, or to brake your excess hyperbolic velocity at Moho.

A couple of nerdy points. Hot staging absolutely still uses a decoupler. Hot staging merely means lighting the upper-stage engine before decoupling. The USA typically had better, more complex vacuum engines and they were worried about debris impingement, so they used separation and ullage motors to decouple, pull the stages apart, and then settle propellants before lighting the upper stage engines. The Soviets, in contrast, put extra shielding on top of their tanks and used open-frame interstages with hollow decouplers so they could light the upper stage engine while the lower stage still had enough residual thrust for propellant settling. Anyone who presses spacebar once to simultaneously decouple the lower stage and activate the upper engine is already hot staging. The LK did not have two stages. Rather, the whole stack used a dedicated braking stage to perform almost all cislunar burns. This stage was used to leave free-return and enter lunar orbit, after which point one cosmonaut would spacewalk down the side of the command module and enter the LK. The command module would separate and the braking stage would perform a deorbit burn. That braking stage would remain attached to the LK through descent, zero out its velocity a few hundred meters above the lunar surface, and then separate to crash. The LK actually had seven engines fed by either two or three turbopumps. The main engine was fixed but throttleable, and provided the ability to hover and descend. It had four small verniers fed from the same turbopump to provide steering. If it failed to light, then two fixed and unthrottleable backup engines, one on either side, would fire for an abort, using RCS for pointing. The LK was capable of making orbit from the lunar surface on either the center engine or the backup engines, but on a nominal ascent all three would fire together. So the LK only had one stage. It did, however, have a “landing frame” with legs and a ladder. This was jettisoned on liftoff from the lunar surface to save weight.

No possible trajectory can do Gilly to Moho in less than 3,710 m/s.

I tried to get fancy with a monoprop orbiter, a Twitch core, and Spider side boosters a la Energia-Buran, but no dice.

Crap. Back to the drawing board then.

Okay, got it up. 1.32 tonnes and it makes orbit with 48 m/s of dV to spare -- enough for a deorbit for sure. I've tested landing, which is...dicey. But doable. Haven't yet tested re-entry but that's next.

I've got it down to 1.2 tonnes with no thrust balancing issues but even so that is not nearly as far down as I expected to be able to get. Trying to refine the ascent profile so I can actually make orbit. EDIT: currently 220 m/s short. Not sure if cleaning up the launch profile will give me enough.

Trying to figure out how to strip this down further. Thinking about making it a little more like Energia-Buran.

That is fascinating. But I suppose it makes sense. Think about it…you need the engines lit in order to do the actual landing; if they don’t, you’re boned anyway. And with high gimbal it’s not hard to imagine them having a lot more control authority than gas thrusters. Probably one place where KSP emulates real life. You need to blanket your rocket with RCS to even come close to the control authority you get from a Vector. It’s not even a contest. Any time you can have your engines lit, you have way more authority than any aerodynamic surfaces, RCS, or reaction wheels can provide. So the kick-flip it is. The best part is no part and the best system is no system. The Ariane 5 can co-manifest and I don’t think it’s a capability that is used often (though I could be wrong about that). Unless you have a single customer sending two comsats to the same GEO destination for whatever reason, you’re always going to end up with a “primary” customer and a “secondary” customer. The GTO delivery will be to the primary customer’s target orbit, and the secondary customer will have to burn extra propellant to move to its target orbit, which reduces mission lifetime. It’s a small burn, but it’s still an issue. And you have the added complexity of multiple integrations. Plus the primary customer will be worried about whether the secondary customer might compromise mission success.

Holy crap I thought this was a simulation That's drone footage y'all

That would be the point. The header tank will be full and downcomers would be as well, so you end up with heat transfer from the plasma to the tiles, from the tiles to the steel, and from the steel to the LOX. LOX boil-off maintains main tank gas pressure, which you need for RCS.

Given that things are still very much in flux I wonder if they would ever consider doing multiple downcomers from the small tank to follow the heat shield and provide secondary cooling.

Look at that beautiful vapor cone. MECO, successful stage separation, and MVac light! Successful fairing separation. These are reused Starlink fairings. She says they will be doing a single-engine landing burn all the way, which makes sense given that this is their first time doing a sixth landing with one booster. Entry burn complete. It feels like it is coming in faster than normal? Or maybe it is just a clearer picture. Falcon has landed!! Congrats SpaceX on the sixth sequential landing of a booster!

Hard to tell just by looking. I wonder if they use hydraulics or if they are single-use crush cores. From the webcast: Is this the first look we've gotten at the resting-nests for the fairing halves? Looks like an inflatable. Falcon 9 is in startup. Liftoff. Go Starlink! Go Falcon 9!

The solar wind (and radiation pressure, to a lesser degree) is responsible for pushing the dust tail of a comet away from the sun, so it's definitely doing SOME work. What do you mean with impossible? Do you have a consistent theory of quantum chromodynamics which predict chemistry like behavior in neutronium matter under conditions in typical neutron star? Or what do you based on statement that such life may be possible? As far as I know neutronium is some kind of liquid, maybe superfluid, and does not form any complex structures. There is absolutely no known reasons to expect any reactions like lifeforms. It is purely science fiction. I'm torn on this point. On the one hand, it's true that we can't speculate endlessly without entering the realm of pure science fiction. I do not expect neutronium life to evolve, for example. But I also don't want to limit imagination. For example, there could be sentient clouds on Jupiter, converting solar energy into rotational eddies that maintain their structure. It's unlikely, but it's entirely possible within the realm of real physics. Life is possible in any place where there is a source of energy and a sink for entropy. Both are required. One reason I don't believe it's realistic to imagine neutronium life is that there is no energy source (other than residual heat) and no entropy sink. Life is a machine that uses energy to artificially decrease its own entropy while increasing the entropy of its surroundings. So you need both to work. Terran life crawls around on the surface of a giant rock, either breathing or creating corrosive gas. Our energy source is the sun and our entropy sink is the soil beneath our feet. Our ability to selectively convert energy into entropy is totally chemical, completely bound up in a very narrow range of temperatures and pressures. Life does not require these conditions to exist or to thrive, but it does require the existence of persistent structures capable of sustaining low-entropy regions. Intelligent life requires those low-entropy regions to be so thoroughly protected that they are able to hold information. And that is the question.

I need to keep this on hand for discussing hypotheticals, haha. It's very interesting. Raptor doesn't need the pintle injector because it is a gas-gas rocket, I believe? Interesting that the turbopump flameout is the limiting factor, rather than a loss of choke in the engine throat. I guess with a super high pressure engine that's to be expected. Are those the new legs or the same design? I think we always knew that.

The velocity of the solar wind is what, 400 km/s? I wonder if that pushes the Earth into a higher orbit. The actual gravity of the Sun won’t change as it swells. Thank you Shell Theorem.

Whoa. That is unbelievable. Original design target was 300 bar. It hit 268 bar in Feb 2019 and reached 300 bar in June 2020.

Right, I was going to say this and then I saw you already had. By the time Earth is anywhere close to the solar corona, the solar wind will start decelerating it pretty rapidly. Huh. I wonder what happens if I use the derived drag equation from Newton's momentum exchange approximation. Assuming Earth remains at its current orbital distance, it sweeps out a volume of 1.199e26 cubic meters each year (cross-sectional area of Earth * orbital semimajor axis * 2π). I'm also getting 1e-16 g/cc from a couple of sources. This means the area swept out by the Earth annually would contain 1.199e13 kg of matter. Earth, of course, is 500 billion times more massive than that, so Earth would only lose 1/500,000,000,000th of its orbital velocity each year. Looks like our intuition was just wrong.