Quote from: Robotbeat on 07/28/2016 04:26 pmIt could be, but it's not going to. At least not before MCT flies.I started at least one thread speculating about a Raptor-based reusable upper stage for Falcon 9/FH, given that hint from the Air Force (which is not new, we've known about that for a quite long while). But now we know from Musk that they're not going to pursue that right now.That leaves the questions of if and when wide open...
It could be, but it's not going to. At least not before MCT flies.I started at least one thread speculating about a Raptor-based reusable upper stage for Falcon 9/FH, given that hint from the Air Force (which is not new, we've known about that for a quite long while). But now we know from Musk that they're not going to pursue that right now.
I don't think it can at all. It will break up from heat load on reentry unless heavily shielded - at which point it's basically a reusable upper stage, which Musk specifically said they aren't working on. The velocity change for a orbital reentry is about 4 to 5x greater, and the max heating rate 20 to 25x greater than what the F9 S1 sees on entry. Even if it's possible to orbit enough fuel retroburn through the peak heating phase (and I STRONGLY doubt that it is), why would they? The stage has a low ballistic coefficient, lots of area to dissipate heat, and slow terminal velocity: shield the front and part of one side, enter nose-first, and keep all the sensitive, expensive parts out of the hypersonic flow and well away from the bow shock. This is exactly how SpaceX envisioned S2 reuse... and they aren't pursuing it.The same goes for BFR. I'm extremely doubtful that orbital reentry using primarily retropropulsion for shock standoff and cooling is possible and more optimal than nose-first entry for a S2 type vehicle. If there's any evidence to the contrary please point it out.
Isn't the mVac nozzle much too flimsy to withstand an engine first re-rentry? Or even a relatively low altitude/low speed (100's kmh) environment?
Quote from: JamesH65 on 07/29/2016 09:28 amIsn't the mVac nozzle much too flimsy to withstand an engine first re-rentry? Or even a relatively low altitude/low speed (100's kmh) environment?Yes, it would be torn to shreds. You'd either have to stow it, or have most of it be disposable.
There are two feasible reentry positions, not just one. Side and engines-first. Both have been tested to varying degrees by SpaceX, Shuttle, DC-X, Blue Origin, as well as simulated.
If second stages are going to be reused and deliver worthwhile payloads, I think most of the braking will need to be done with friction and not propulsion.Matthew
...Second even at the time of the release of that infamous video it was obvious that the 2nd stage recovery shown was Holly Wood nonsense and nothing more then a placeholder, nose first re-entry is impossible because it is totally unstable, the engine is most massive part of a 2nd stage and this will dictate an engine first entry. Second it was clear that the nose of a second stage can't do the basic job of attaching a payload if it is a smooth heat shield....
... it is totally unstable, the engine is most massive part of a 2nd stage and this will dictate an engine first entry....
...it was clear that the nose of a second stage can't do the basic job of attaching a payload if it is a smooth heat shield.The only feasible entry is engine first, which means either a shield that moves to cover the engine...
Seems like a reusable Raptor 2nd stage could be done if it entered and landed nose first. Add upside down landing legs near the top of the stage, TPS around the 'nose' (perhaps even a bit oversized diameter, to protect the body of the stage), some Super Dracos for landing assist, and grid fins near the engine.