It's not that hard to make an SSTO, but it is very hard to make an SSTO that will reenter and land in one piece. A Delta IV first stage launched alone could make it to orbit, but that would no longer be the case if you added enough recovery gear to it that it would make it down to the ground intact.The two-stage approach that SpaceX have taken is attractive because most of the vehicle can be recovered without having to worry about covering the first stage in heavy reentry-grade TPS. It may take a significant advance in TPS to really make an SSTO worth it.
Boosted SSTO makes the most sense. The boosters are reusable and flyback, the core refuel-able in LEO.
Quote from: TaylorR137 on 11/17/2013 07:49 amBoosted SSTO makes the most sense. The boosters are reusable and flyback, the core refuel-able in LEO.This may be just semantic, but if you have boosters then it's not an SSTO. Otherwise the shuttle would have been considered an SSTO.
I suppose this topic deserved its own thread in the sense that it was a bit more than a conversation about 'possible configurations for Raptor-based rockets.'Again, I'd like to do the math when I have time, but I am aware that SpaceX has already met the dry mass fractions required to put a non-zero payload in orbit with an SSTO with the intended specs of the Falcon Heavy boosters. The reason one stages a rocket is to increase (or make non-negative) the payload fraction. However, when we add reusability to the equation, the first stage RTLS actual invites a disadvantage in delta-v which may or may not exceed the disadvantage of SSTO. Even if the two are not on the same order, the feasibility for rapid reusability and manufacturability of an SSTO may exceed the TSTO model and thus generate a potential cost savings.Does anyone have any thoughts on the matter? Some numbers might greatly aid the discussion as well.
first-stage-reuse reduces them by 70%-80%.
I'm not sure on the argument of a SSTO with reuse versus a TSTO with full reuse. You save greatly on TPS mass by only putting it on sections that actually have to deal with hypersonic re-entry. Also, the complication of a single staging mechanism isn't that bad, especially if it doesn't use any explosives to do so.Granted you save some tank-end mass (four tank-ends removed) and engine mass, but you lose a lot in extra TPS and strengthening, not to mention tank dead weight being brought to orbit. TSTO also allows incremental re-use rather than either full re-use or complete non-re-use.
Elon has talked in one of his interviews about reusability and has pointed out that it has everything to do with how big of a fraction of your rocket can you deliver to orbit. Reusabiliy part will take about 2%. If you can make your rocket deliver 4%, then you can deliver 2% and still get your rocket back. It's much easier to get robust and reliable 4% TSTO than SSTO.`So, if can we make a robust SSTO that goes well over 2%, then it can work. Can we and at what price?
The only SSTO design that has a decent chance of working is as far as I can see is Skylon, but that is still several years before it can be tested. They still need to prove the engines can work. The idea that a big low density airframe can reenter at hypersonic speeds, be strong enough to withstand dynamic pressure and heat without the need for an ablative TPS needs to be proven.Elon is skeptical about air breathing launch vehicles in general, but I think he wouldn't consider the technology too closely since it can't scale up to MCT class or go BEO, so why bother?