Right... I was thinking long term. It's clear that it would require more in-orbit capability, and an engine redesign that makes it easily detachable from the support structure and nozzle. And as you say, it doesn't make sense to bring up the US to ISS orbit, so you would have to do it at the altitude where the upper stage is inserted. If you'd be able to fit more than one engine inside, you wouldn't eat up all the return capability. Only some Dragons would then return engines. Others would operate normally.
OK, I see. So it would make more sense to detach and bring the the 500 kg Merlin up to ISS orbit (as part of the unpressurized cargo) than bringing the 5000 kg Dragon down to the upper stage's orbit?You could store upper stage engines at ISS (or in whatever future space station) and bring them down to earth in batches.
OK, I see. So it would make more sense to detach and bring the the 500 kg Merlin up to ISS orbit (as part of the unpressurized cargo) than bringing the 5000 kg Dragon down to the upper stage's orbit?
Quote from: Joel on 07/01/2012 01:25 pmOK, I see. So it would make more sense to detach and bring the the 500 kg Merlin up to ISS orbit (as part of the unpressurized cargo) than bringing the 5000 kg Dragon down to the upper stage's orbit?No, either. There is no sense to do either. There is no room nor time nor benefit.
I realize that the benefit is limited, would you say that this concept is more (un)realistic than adding a heat shield to the second stage, reenter it and land vertically on the launch site?
Just a clarification, what do you mean by "no room"? Inside the Dragon or in the ISS?
Just a clarification, what do you mean by "no room"? Inside the Dragon or in the ISS? I mean, you don't need to store the engines inside the station.I guess a limitation would be to get the Merlin into the Harmony node, but that's just a design problem of the ISS. A future space station could be designed to allow this.
As for fitting it into the Dragon, see above. At least one, maybe more than one should fit from what I can tell. Without support structure and nozzle that is.
The benefit would be that you're able to reuse the engine, which is the expensive part of the stage
The benefit would be that you're able to reuse the engine, which is the expensive part of the stage, without the dead weight associated with a heat shield, making the upper stage sturdy enough for reentry and extra propellant for reentry and landing.Of course, some extra propellant would be needed to raise the altitude of the 500 kg engine, but that should be small in comparison.Also, once you've designed the system, it should be cheap to operate, because you will probably want to bring a lot more cargo up into LEO than down from LEO. Especially if you are servicing a space station.
Or would you be able to land the upper stage vertically with the vacuum nozzle attached/extended?
Quote from: Joel on 07/01/2012 02:43 pmOr would you be able to land the upper stage vertically with the vacuum nozzle attached/extended?The reusability video shows it retracting. Flexible plumbing would be complicated so I suspect it's an entire outer sheath with the engine/propellant tanks as a movable unit inside.
Using the sheath might work, but you can't keep it around the nozzle when it fires, since the radiated heat from the nozzle will disintegrate it. (and if not, will melt the nozzle)Off all the things that SpaceX showed, this second stage recovery trick is the biggest head-scratcher for me. Options that I see are:- Retracting engine assembly- A sliding sheath (So basically a retracting "everything")- Drop the nozzle extension- Make the nozzle extension survive rentry (face up) and have a large landing gear.This should be a new thread.
If they're going to have a sheath around the nozzle, would it make sense to just retain the interstage (or some portion of it) to serve the purpose?