The biggest issue (to me) with the 2nd stage reentry is going to be how to make the stage enter nose first - since the it will be tail heavy. (engine + landing gear) So how can they move the CG forward? The draco/superdraco propellant tanks would have to be located at the front, but would it be enough?Then again we shouldn't read too much into the specifics of that video. They did state that it was very rough version that omitted/changed significant details on purpose.
Put the tanks for propellant for the Super Draco's at the top to offset the weight of the engine/thrust structure/legs.
Quote from: pippin on 07/01/2012 05:02 pmYou are wrong. Hehe... Only in NSF can someone be wrong for gathering all the various ideas described so far...
You are wrong.
And if the nozzle has two sections, this solves the VAC/SL requirement.
Launch, Orbit, Entry, Landing
Quote from: modemeagle on 07/03/2012 03:42 amLaunch, Orbit, Entry, LandingLaunch stage 1 (under interstage) - (1), correct only for first stage burnLaunch stage 2 (u/s in operation) - (2)Post-separation loiter - like (1), but with nozzle retracted [not (2)]On-orbit burn - (2)Reentry - (3), correct as depictedLanding - (4), correct as depictedcheers, Martin
I've been thinking, if you can tuck the main nozzle all the way back, do you really need an interstage? May be they integrate the landing structure on what's currently an interstage. You get horrible fmp, but you get more recoverable.
I meant with the allegation that the nozzle is the "biggest head-scratcher".But you are right, you also said "for me" which is of course a subjective statement that can't really be "wrong".
Quote from: baldusi on 07/03/2012 02:47 pmI've been thinking, if you can tuck the main nozzle all the way back, do you really need an interstage? May be they integrate the landing structure on what's currently an interstage. You get horrible fmp, but you get more recoverable.ETA: So, they launch with the nozzle fully retracted, and extend it before firing? It would complicate staging, but that may be tolerable. Another possible arrangement, if they stage out of the atmosphere, would be not to retract the nozzle, but instead to have panels around it which fold up, leaving the nozzle (which is its own radiator) exposed. This would have fewer moving parts than a retractable nozzle/engine, and no moving plumbing. But in the atmosphere, the panels would be ripped off instantly, though, so this would strongly constrain the mission profile, and put the staging point high enough that it might well compromise recovery of the first stage.Originally wrote, assuming fixed nozzle (duh): They can't retain much of the interstage without changing something else. The current second stage nozzle is radiatively cooled; leave it inside anything that absorbs the radiation or reflects it back and it'll melt, or melt the shroud, or both. (I proposed this on another thread, and got instant proof that IANARS.) And an interestage which doesn't reflect or retain the radiation is... not the current model.If they switched to regenerative cooling for the nozzle, it might be possible to make this work, at a weight penalty --- but only if there's enough fluid flowing through to cool a very large nozzle. (The F-1 was roughly comparable, at 12.2 feet in diameter, but it had a lot more fuel flowing through, only used regenerative cooling for part of the nozzle, and didn't have to run in a vacuum...)
Quote from: MP99 on 07/03/2012 12:46 pmQuote from: modemeagle on 07/03/2012 03:42 amLaunch, Orbit, Entry, LandingLaunch stage 1 (under interstage) - (1), correct only for first stage burnLaunch stage 2 (u/s in operation) - (2)Post-separation loiter - like (1), but with nozzle retracted [not (2)]On-orbit burn - (2)Reentry - (3), correct as depictedLanding - (4), correct as depictedcheers, MartinIf you're going to fire your main engine for de-orbit, then what would be the point of retraction for orbit? Adds the risk that it won't extend for the burn (not that it will really matter since a burn at 60% thrust is ~ 2 seconds).
Legs retract back to the parallel (launch) position for the coast phase and while the stage reverses under SuperDracos. Nozzle (or the whole Merlin?) is also retracted during this phase - presumably after the nozzle has cooled. Don't really understand this - why not leave legs splayed & nozzle deployed for this phase? Protection against MMOD? I'd have though this wasn't much of an issue at u/s apogee?
Quote from: pippin on 07/03/2012 12:25 pmI meant with the allegation that the nozzle is the "biggest head-scratcher".But you are right, you also said "for me" which is of course a subjective statement that can't really be "wrong".Sure, and "protection" was the wrong emphasis on my part. More broadly speaking, it's what this thread drifted to discussing.From what I read so far, the suggestion that the stage can enter engine-first (while firing?) didn't have many supporters, correct? My only contribution to this is that I believe it will be a fundamentally "well off the beaten path" concept, and that's not the SpaceX way. New ideas at the system level - the more the merrier. New basic concepts? not now.
Quote from: meekGee on 07/03/2012 04:58 pmQuote from: pippin on 07/03/2012 12:25 pmI meant with the allegation that the nozzle is the "biggest head-scratcher".But you are right, you also said "for me" which is of course a subjective statement that can't really be "wrong".Sure, and "protection" was the wrong emphasis on my part. More broadly speaking, it's what this thread drifted to discussing.From what I read so far, the suggestion that the stage can enter engine-first (while firing?) didn't have many supporters, correct? My only contribution to this is that I believe it will be a fundamentally "well off the beaten path" concept, and that's not the SpaceX way. New ideas at the system level - the more the merrier. New basic concepts? not now.I would be interested to know what the effects on an engine with an effective exhaust velocity of 3.5 km/s would have while firing directly into the atmosphere at over 6 km/s.How would this effect the operation of the engine (thrust, stability)
Or fire two engines face to face.
Quote from: modemeagle on 07/03/2012 06:41 pmQuote from: meekGee on 07/03/2012 04:58 pmQuote from: pippin on 07/03/2012 12:25 pmI meant with the allegation that the nozzle is the "biggest head-scratcher".But you are right, you also said "for me" which is of course a subjective statement that can't really be "wrong".Sure, and "protection" was the wrong emphasis on my part. More broadly speaking, it's what this thread drifted to discussing.From what I read so far, the suggestion that the stage can enter engine-first (while firing?) didn't have many supporters, correct? My only contribution to this is that I believe it will be a fundamentally "well off the beaten path" concept, and that's not the SpaceX way. New ideas at the system level - the more the merrier. New basic concepts? not now.I would be interested to know what the effects on an engine with an effective exhaust velocity of 3.5 km/s would have while firing directly into the atmosphere at over 6 km/s.How would this effect the operation of the engine (thrust, stability)I think strapping a rocket engine backwards to the top of an SR-71 and firing it would be fun to try. We just need to find a test pilot that is actually suicidal rather than just regular crazy.
I can't help feeling that SpaceX's approach is going about the problem the wrong way. We already know how to make engines survive reentry - it worked just fine on the shuttle.If both the Dragon and second stage reach orbit, and both are to re-enter, land and be reused, what is the benefit of having them be two separate vehicles? Why not combine them? The second stage tank is not that big. Take the DreamChaser lifting body approach, and scale it up to include the tank and engine inside the fusilage. The empty tank makes the vehicle "fluffier", easing re-entry heating. The engine never has to face reentry heat or fire supersonically. Landing fuel isn't carried so the vehicle structure can be larger. The entire second stage glides to a runway landing, same as the shuttle, but isn't nearly as big as the shuttle.Maybe it would have to be sized for the FH, but if the strap-on cores have boost-back and the entire second stage is reused, that should be quite cost effective.Capsules make sense if the entire rest of the rocket is being thrown away and the capsule is all that has to land. But if the second stage is flying back and landing, is a capsule still the best choice vs. an integrated lifting body?
If both the Dragon and second stage reach orbit, and both are to re-enter, land and be reused, what is the benefit of having them be two separate vehicles? Why not combine them? The second stage tank is not that big.