Quote from: LMT on 10/08/2022 07:09 pmQuote from: InterestedEngineer on 10/08/2022 04:41 pm...this maneuver gets you anywhere you want to go in the Solar system, at deltaVs so high the online porkchop calculators can't handle it.Getting to the outer solar system is straightforward. Getting back isn't.As with a notional 2-year Starship Jupiter mission, delta-v far exceeds depot capacity, whether in LEO, HEEO, or elsewhere. Depots must be supplemented, somehow. In that mission:- (Directional) laser propulsion was based in LEO and LJO.- (Omnidirectional) methalox depots were based in LEO and on Callisto.Together, and only together, they gave thrust vectors for mission success.Some such network of pre-positioned directional and omnidirectional propulsion solutions would seem necessary for crewed missions to the outer solar system.In practice, mission planners would optimize use of the network, in the spirit of Ishimatsu et al. 2016. That is, applying an extended network flow model to the logistics system.Q: To support outer solar system Starship missions, where might you base the next directional and omnidirectional propulsion solutions? What are some further good moves on the logistics chessboard?Refs.Ishimatsu, T., de Weck, O.L., Hoffman, J.A., Ohkami, Y. and Shishko, R., 2016. Generalized multicommodity network flow model for the earth–moon–mars logistics system. Journal of Spacecraft and Rockets, 53(1), pp.25-38.By "anywhere in the solar system" I meant one way flybys.
Quote from: InterestedEngineer on 10/08/2022 04:41 pm...this maneuver gets you anywhere you want to go in the Solar system, at deltaVs so high the online porkchop calculators can't handle it.Getting to the outer solar system is straightforward. Getting back isn't.As with a notional 2-year Starship Jupiter mission, delta-v far exceeds depot capacity, whether in LEO, HEEO, or elsewhere. Depots must be supplemented, somehow. In that mission:- (Directional) laser propulsion was based in LEO and LJO.- (Omnidirectional) methalox depots were based in LEO and on Callisto.Together, and only together, they gave thrust vectors for mission success.Some such network of pre-positioned directional and omnidirectional propulsion solutions would seem necessary for crewed missions to the outer solar system.In practice, mission planners would optimize use of the network, in the spirit of Ishimatsu et al. 2016. That is, applying an extended network flow model to the logistics system.Q: To support outer solar system Starship missions, where might you base the next directional and omnidirectional propulsion solutions? What are some further good moves on the logistics chessboard?Refs.Ishimatsu, T., de Weck, O.L., Hoffman, J.A., Ohkami, Y. and Shishko, R., 2016. Generalized multicommodity network flow model for the earth–moon–mars logistics system. Journal of Spacecraft and Rockets, 53(1), pp.25-38.
...this maneuver gets you anywhere you want to go in the Solar system, at deltaVs so high the online porkchop calculators can't handle it.
...for less than 1/10 the cost of the SLS you can refuel a Starship in ~GTO and get anywhere else with Vinf of 15km/sec. For example it drops Mars down to about 68 days, assuming Starship can actually slow down in the Mars atmosphere...
Yes, with many tankers and SH launches, understood. Orbit and return maneuvers are vastly harder, but vital for most useful missions.
Also, your "turn & burn at Jupiter" isn't a remotely realistic Starship maneuver. Other propulsion is needed.
It's a false assumption. Your entry speed is north of 30 km/s. With such immense KE, EDL is not possible.
I'm not sure I get how Vinf 15km/sec leaving Earth SOI gives you 30km/sec at Mars atmosphere.
Just to be sure I properly understand you: You're talking about refueling while accelerating, right? That is, you would:a) launch a tanker and an LSS. (Each with 1500t fuel capacity.)b) fully fuel both of them in LEO from a (rather large) depot. (Or two depots.) c) couple the tanker to the LSS for refueling.d) both of them fire together in formation, with the tanker continuously keeping the LSS topped up.e) when the tanker is almost dry, it stops firing, disconnects, and reels in the fuel line.f) at apogee, the tanker fires just a little bit to lower perigee to enable reentry.g) the LSS goes on firing until it reaches TLI--arriving at the moon with about 500t extra fuel.
Quote from: redneck on 10/08/2022 10:02 pmI'm say hard couple the ships together to control the variations. Formation flying while refueling would be even riskier.Formation flying while refueling is what US Air Force has been doing since the late 1940s.The trick is to not be under relative acceleration. That's the default for spacecraft not under thrust, whether it's HEEO, LEO, or Luna orbit.Other than radiation, there's no difference between a refueling procedure in orbit around Luna, HEEO, or LEO, although the refueling has to be not controlled by Earth because of lag problems in the first two cases. Since Dragon is docking autonomously I think they'll figure out how to do refueling > 0.01 light second away from Earth.If you are worried about formation refueling, then LEO refueling won't work either, and the entire architecture of Starship is doomed. Somehow I don't think so.
I'm say hard couple the ships together to control the variations. Formation flying while refueling would be even riskier.
Quote from: InterestedEngineer on 10/08/2022 10:39 pmQuote from: redneck on 10/08/2022 10:02 pmI'm say hard couple the ships together to control the variations. Formation flying while refueling would be even riskier.Formation flying while refueling is what US Air Force has been doing since the late 1940s.The trick is to not be under relative acceleration. That's the default for spacecraft not under thrust, whether it's HEEO, LEO, or Luna orbit.Other than radiation, there's no difference between a refueling procedure in orbit around Luna, HEEO, or LEO, although the refueling has to be not controlled by Earth because of lag problems in the first two cases. Since Dragon is docking autonomously I think they'll figure out how to do refueling > 0.01 light second away from Earth.If you are worried about formation refueling, then LEO refueling won't work either, and the entire architecture of Starship is doomed. Somehow I don't think so.Given that, it seems like the original suggestion about transferring the propellant during the boost would work out. Get the full value of the extra propellant burned during the impulse burn from LEO. I don't think you were suggesting complete transfer during max boost. Transferring during acceleration does address settling problems as opposed to microgravity transfer. One question is how low can the acceleration be without gravity losses eating too much into the potential gains? RL10 class with deep throttling?
...No prop transfer occurs!!! It's only a pusher!!!!f) The pusher adds just enough delta-v to get the EDLC-LSS to go HEEO-LS-EDL on its 1500t of prop.g) The pusher detaches and the EDLC-LSS immediately burns to TLI...
Quote from: Barley on 10/08/2022 12:07 amQuote from: TheRadicalModerate on 10/07/2022 07:40 pmThe fact that SLS and Orion will have less flight experience is irrelevant to the LSS. Both SpaceX and NASA will do whatever they can to minimize risks, especially if it's cheap or easy to do so. This is one that's both.Avoiding a second refueling avoids some risks but it adds others.It requires a custom extended tank, which adds risk.I don't think it's a custom extended tank. There are even more good reasons to go with a 1500t tank for lift tankers than there are for the LSS, not the least of which is that it doesn't require sending two tankers to NRHO for Option B.Also, remember that "extended" really means "with ring segments, intertank bulkhead, and LCH4 dome rearranged." That's not nothing, but as modifications go, it's not as bad as a lot of the mods that SpaceX has to make for LSS no matter what.QuoteIt also reduces margin. The extra refueling lets you throw mass at other risks. It also reduces schedule risk, and in particular a risk of SS underperforming; if it gets to orbit it can complete the mission with two refuelings.Your argument about margin is well-taken--if you're talking about a 1200t LSS. But even there, when I added in FPR and fixed prop losses, things worked out OK in a low HEEO. I wouldn't want to use that method with a crew, but it's got pretty good margin for an uncrewed pre-positioning of the LSS in NRHO.However, it's a lot more janky than just going with 1500t tanks. Even after adding FPR, fixed losses, and boil-off allowances, the 1500t LSS gets back from the surface to NRHO with several tonnes of usable prop.QuoteThere will be no delay trying to make weight by making the windows so thin they are at risk from a finger tap.Well, I've got other people on the thread complaining that my dry mass and crew module numbers are too conservative. And again, 1500t of prop hides a multitude of sins. There's a lot of mass margin here.QuoteAvoiding a refueling is not a no brainer, you have to evaluate all the risks being added against the risk of a refueling, unless you just assign each refueling infinite risk by fiat.That's fair, but assigning high risk to a procedure with which you have little operational experience is appropriate. NB: Even if there turns out to be a lot of experience with tankers fueling depots in VLEO, there will be considerably less experience refueling stuff in HEEO. Could SpaceX load up on dummy refueling missions to work this out? Sure. But why bother if there's a better way to manage the risk?The other factor here is risk tolerance. In a perfect world, this wouldn't change over time. However, HLS is a high enough profile project, both for NASA and SpaceX, that reducing tolerance to ensure that both Option A flights go well is a good political move--especially since NASA wrung their hands about operational complexity in the source selection statement, and Blue Origin used the conops to fling FUD around during the protest and appeal process.
Quote from: TheRadicalModerate on 10/07/2022 07:40 pmThe fact that SLS and Orion will have less flight experience is irrelevant to the LSS. Both SpaceX and NASA will do whatever they can to minimize risks, especially if it's cheap or easy to do so. This is one that's both.Avoiding a second refueling avoids some risks but it adds others.It requires a custom extended tank, which adds risk.
The fact that SLS and Orion will have less flight experience is irrelevant to the LSS. Both SpaceX and NASA will do whatever they can to minimize risks, especially if it's cheap or easy to do so. This is one that's both.
It also reduces margin. The extra refueling lets you throw mass at other risks. It also reduces schedule risk, and in particular a risk of SS underperforming; if it gets to orbit it can complete the mission with two refuelings.
There will be no delay trying to make weight by making the windows so thin they are at risk from a finger tap.
Avoiding a refueling is not a no brainer, you have to evaluate all the risks being added against the risk of a refueling, unless you just assign each refueling infinite risk by fiat.
Quote from: TheRadicalModerate on 10/08/2022 04:56 amNB: Even if there turns out to be a lot of experience with tankers fueling depots in VLEO, there will be considerably less experience refueling stuff in HEEO.Why would HEEO refueling add novelty? What is added that is not demonstrated at LEO? The utility of the operation is another question and I have no opinion. Just trying to follow the arguments.
NB: Even if there turns out to be a lot of experience with tankers fueling depots in VLEO, there will be considerably less experience refueling stuff in HEEO.
Quote from: redneck on 10/08/2022 08:20 amA few days ago I mentioned the concept of tanker and cargo Starship mated for the burn from LEO towards the moon. Mainly I brought it up because I hadn't noticed it in this discussion. It didn't seem to be a popular idea both on the technical side and even whether it would be useful. I concede that the technical end may be more difficult than most would like. Possibly to the point of not being worthwhile.As for the usefulness if it could be implemented, I didn't make the time to check my assumptions until this afternoon. Did a bit of BOTE to see where I would end up. The way I see it, if the tanker would detach at ~2,500 m/s and fall back to reenter while the cargo Starship kept thrusting. The Starship would have a mass ratio of about 1.5 remaining to NHRO rendezvous. It seems to me that reaching that rendezvous with an extra 500 tons of propellant on board would be far from useless. Just to be sure I properly understand you: You're talking about refueling while accelerating, right? That is, you would:a) launch a tanker and an LSS. (Each with 1500t fuel capacity.)b) fully fuel both of them in LEO from a (rather large) depot. (Or two depots.) c) couple the tanker to the LSS for refueling.d) both of them fire together in formation, with the tanker continuously keeping the LSS topped up.e) when the tanker is almost dry, it stops firing, disconnects, and reels in the fuel line.f) at apogee, the tanker fires just a little bit to lower perigee to enable reentry.g) the LSS goes on firing until it reaches TLI--arriving at the moon with about 500t extra fuel.But I think we previously figured that a fully fueled tanker in LEO could reach the moon with about 500t of fuel still in the tank, so (if two refueling operations were allowed), you'd only be saving a little bit over having both ships accelerate to TLI independently and then have them rendezvous for refueling at any point thereafter. (And have the tanker do a free return or something like it.) Is that right?Anyway, if NASA is worried about the risks of refueling in LEO, I think the risks of refueling while accelerating will really send them into orbit. (So to speak.) :-)
A few days ago I mentioned the concept of tanker and cargo Starship mated for the burn from LEO towards the moon. Mainly I brought it up because I hadn't noticed it in this discussion. It didn't seem to be a popular idea both on the technical side and even whether it would be useful. I concede that the technical end may be more difficult than most would like. Possibly to the point of not being worthwhile.As for the usefulness if it could be implemented, I didn't make the time to check my assumptions until this afternoon. Did a bit of BOTE to see where I would end up. The way I see it, if the tanker would detach at ~2,500 m/s and fall back to reenter while the cargo Starship kept thrusting. The Starship would have a mass ratio of about 1.5 remaining to NHRO rendezvous. It seems to me that reaching that rendezvous with an extra 500 tons of propellant on board would be far from useless.
Quote from: TheRadicalModerate on 10/07/2022 08:41 pmI don't think they need a depot. In effect, they are depots, or at least spacecraft with good passive resistance to boil-off. So you can refuel them long before the crew shows up, using plain ol' tankers that go out to NRHO via BLT and straight back to EDL.I know. I'm just liking the model that says Starships mate with depots, but not with each other, since it makes all the plumbing very unambiguous. It also lets the refueling be completely asynchronous. In this vision, a) a steady stream of tankers keeps the LEO depot full, b) occasionally a tanker fills up from the depot, flies to the moon, and pumps ~500t of prop into that depot (which really does achieve ZBO), so c) whenever an LSS needs to refuel, there's always fuel for it either in LEO or at Gateway.Quote from: TheRadicalModerate on 10/07/2022 08:41 pmI expect Option B (and Appendix P) HLSes to have fairly short lives, due to dust contamination. It may be that SpaceX would do better using an EDL-capable LSS, if for no other reason that you can completely clean and refurbish it on the ground. (You can also integrate new heavy cargoes into it, which an Option B LSS can't do.) But this definitely requires refueling in HEEO or cislunar.This leads me to wonder whether it's possible to do that at Gateway. Or, conversely, what is the minimum it would take to do the necessary maintenance and checkout at Gateway, rather than returning the LSS to Earth? (Assuming you can skip the static fire.) :-)
I don't think they need a depot. In effect, they are depots, or at least spacecraft with good passive resistance to boil-off. So you can refuel them long before the crew shows up, using plain ol' tankers that go out to NRHO via BLT and straight back to EDL.
I expect Option B (and Appendix P) HLSes to have fairly short lives, due to dust contamination. It may be that SpaceX would do better using an EDL-capable LSS, if for no other reason that you can completely clean and refurbish it on the ground. (You can also integrate new heavy cargoes into it, which an Option B LSS can't do.) But this definitely requires refueling in HEEO or cislunar.
On further reflection, I am even more convinced that all of the specialized refuelling hardware should be in the depot and the SSs should be at most minimally modified: the best part is no part.All SS already have a mating connection for thrust, namely the big nine-meter ring that connects to the SH. The depot should implement the SH side of this connection beneath a disposable fairing at the nose. After the fairing is discarded the depot is a cylinder whose top surface looks like the top surface of an SH. The depot will dock nose-to-tail with the SS. The fuel transfer will be via an extendable QD mechanism that is stored beneath the mating ring and is also covered by the disposable fairing. It extends out, up, and around to mate with the SS QD connection. Fuel transfer is done while under a small amount of thrust provided by the depot. Exactly how docking and locking will be accomplished will require actual engineering instead of hand-waving and will depend on the current design of the existing interface. Worst case: use a nine-meter version of the "soft docking" hardware from the IDSS that provides six degrees of freedom through a limited range of motion to complete the soft docking. I strongly suspect this is overkill and real engineers will come up with a simpler system.
It would be great to be able to do repair at gateway and as much as I'd like it, it doesn't seem practical.
Can you imagine changing out your cars water pump in a space suit in zero g? They do EVA stuff like this on the ISS only after modeling and scripting every move on the ground and still run into problems.
One optimization we've never seen on a rocket is on orbit maintenance and repair. The day is coming but probably not for another generation or two of rockets. I'd guess that there will be minor tweaks in this direction but the big change will be when they move to on orbit assembly.
I do kind of like the idea of the depot securely attaching to the vehicles it refuels. I'm just wondering how the plumbing would work.
LOXSAT 1 will test a suite of CFM technologies previously developed and ground tested. CFM technologies include:Active and passive thermal controlCryogenic chill down and transferPressure controlGround densificationFluid surface visualization toolsAutogenous vs. helium pressurizationLiquid acquisition devices (LAD)Zero boil off (ZBO) with pump mixingHigh capacity 90K cryocoolersGround to flight insulationLow conductivity supportsZero-g chill down and transferCryogenic quick disconnectsGround densification for thermal energy storage
Quote from: DanClemmensen on 10/09/2022 06:24 pmOn further reflection, I am even more convinced that all of the specialized refuelling hardware should be in the depot and the SSs should be at most minimally modified: the best part is no part.All SS already have a mating connection for thrust, namely the big nine-meter ring that connects to the SH. The depot should implement the SH side of this connection beneath a disposable fairing at the nose. After the fairing is discarded the depot is a cylinder whose top surface looks like the top surface of an SH. The depot will dock nose-to-tail with the SS. The fuel transfer will be via an extendable QD mechanism that is stored beneath the mating ring and is also covered by the disposable fairing. It extends out, up, and around to mate with the SS QD connection. Fuel transfer is done while under a small amount of thrust provided by the depot. Exactly how docking and locking will be accomplished will require actual engineering instead of hand-waving and will depend on the current design of the existing interface. Worst case: use a nine-meter version of the "soft docking" hardware from the IDSS that provides six degrees of freedom through a limited range of motion to complete the soft docking. I strongly suspect this is overkill and real engineers will come up with a simpler system. Doesn't this result in a lot more plumbing, though? (At least, on the depot.) I've been assuming that the depot is little more than a Starship with extended tanks, meaning it fills/drains through a QD port at the bottom. That port would get replaced with a gender-swapped hose of some kind (I'm fuzzy on exactly how this would work, but something a lot like the hoses in the existing ground support equipment that fills them up on the pad) but the interior of the depot would be almost identical to that of a Starship. That means they have to be side-by-side to refuel OR the hose needs to be really long, which (I'm told) introduces a lot of problems.I do kind of like the idea of the depot securely attaching to the vehicles it refuels. I'm just wondering how the plumbing would work.