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Seeing as the Falcon 9R first stage is close to being reusable, could it be the basis for an SSTO rocket? In other words, does it have enough performance to make it into orbit, and then boost back and land, say with no payload (or second stage) at all, or just a very small one?

I assume not, but I haven't seen actual figures. How far away is it?

And what about a Falcon Heavy (reusable of course)?

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    $\begingroup$ IF there is an LEO Gas Station then yes it can as well as the 2nd stage can return. IF said Gas station is supplied from resources on the Moon then the cost most certainly should make this economical for SpaceX and Blue Origin .... and the U.S. Airforce $\endgroup$ – Enigma Maitreya Jun 2 '17 at 17:45
  • $\begingroup$ Excepting the multi-billion expenditures to build such a fuel plant on the moon though. That is no easy task with the tools we have available today. $\endgroup$ – Mike Wise Jun 2 '17 at 20:37
  • $\begingroup$ But there are other possibilities too, like putting a refueling tug into orbit, and periodically refueling it with an FH. Or maybe shooting fuel into orbit with a railgun. We will see. $\endgroup$ – Mike Wise Jun 3 '17 at 13:00
  • $\begingroup$ That is correct there are many ways to do this, what we need is a sustainable and cheap method to do this. With Fuel in Space then Vehicles in space will follow. Lunar made fuel will most likely be the cheapest once established. My goal is to always be independent of Earth Resources at the earliest possible time. With the Water Ice deposits on the Moon and possible H3 mining we can fuel both Chemical and Fusion drives. My plan would be to use the Water Ice for fuel for as short a time as possible. $\endgroup$ – Enigma Maitreya Jun 3 '17 at 13:10
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    $\begingroup$ It is a good idea and should be applicable to other things, food, water, source material for 3D printing etc. But eventually we want to be independent of Earth's resources. <- Just my opinion $\endgroup$ – Enigma Maitreya Jun 3 '17 at 13:21
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According to Spaceflight 101, the fueled mass of the first stage is 403 tons, and empty mass 18 tons. Its specific impulse ranges from 282 to 311 seconds going from sea level to vacuum, implying exhaust velocity of 2766-3050 m/s. Plugging those values into the rocket equation gets you somewhere between 8600 and 9500 m/s of delta-v. I don't know the exact specific impulse curve through the atmosphere and can't be bothered with the calculus anyway, but I'd guess it's nearer the low end of the range since the rocket is spending more time moving relatively slowly in the lower, denser part of the atmosphere.

Delta-v to low earth orbit is about 9.3km/s to 10km/s depending on launch site and destination orbit, so F9R doesn't have quite enough oomph to get there.

It's pretty close, to be sure. Could it be modified to do it? The F9 has already been "stretched" once (F9 1.0 to F9 1.1) and the engines improved a couple of times, and they're hoping to increase the performance another 15% (mainly by increasing the fuel density with further cooling). If they can achieve that, then they should be just barely able to orbit the first stage, with better than 9900 m/s of delta-v -- and zero payload.

If I've got the math right, in the Falcon Heavy crossfeed situation, again with no upper stage or payload, the boosters would provide another 2800 m/s of delta-v to the stack, for a total of about 12 km/s, so it can comfortably reach LEO. As far as the rocket equation is concerned, though, that's a two-stage rocket; it just has some engines in the wrong place.

Re-entry and recovery, on the other hand, is probably impossible. The first stage is designed to withstand a much more modest aerodynamic situation than re-entry from orbital speed. Structurally and thermally, it's a completely different world.

SpaceX would like to make the second stage reusable as well as the first, which would require them to solve orbital re-entry for a rocket stage but on a much smaller scale. Even if they don't accomplish that, a fully reusable first stage would offer them a huge competitive advantage. They have no need to do SSTO.

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    $\begingroup$ There's a substantial performance upgrade coming this year with uprated Merlin "1D+" engines and subcooled propellants for increased density. I'm not sure how accurate the numbers on your reference are - SpaceX isn't very public about their specs - but if they're correct then the upgrades would likely be sufficient to get a standalone first stage into orbit. However, reentry and landing is a whole 'nother matter. $\endgroup$ – pericynthion Mar 24 '15 at 6:09
  • $\begingroup$ Enroute to the barge, the first stage has done a boost back burn to kill it's eastward velocity. RTLS (Return To Launch Site) would entail a more substantial boost back burn. And then terminal velocity must be killed just prior to landing. Does anyone know how much delta V the boost back and killing terminal velocity requires? $\endgroup$ – HopDavid Mar 24 '15 at 15:28
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    $\begingroup$ Surviving an 8 km/s re-entry takes a heat shield and strong structure. I am not sure how much this would add to the dry mass of the first stage. $\endgroup$ – HopDavid Mar 24 '15 at 15:30
  • $\begingroup$ If you're going to orbit, you wouldn't really boost-back for RTLS, you'd take the long way around. So a de-orbit burn, and whatever delta-v you'd need to manage your descent trajectory, and the terminal hover-slam burn. As a Kerbal-level rocket scientist, I'd guess 2-3km/s? But you're right that the structural requirements for re-entry would probably be a bigger problem than the delta-v. $\endgroup$ – Russell Borogove Mar 24 '15 at 16:38
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    $\begingroup$ I know the question is a lot more complicated, but how does the Falcon Heavy change things? The two side boosters empty early and fly back, leaving the center core with a lot of initial velocity and potentially (with cross-feed) a full tank. That should be enough right? Of course it is not really SSTO anymore... $\endgroup$ – Mike Wise Mar 24 '15 at 17:09
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Yes, it can. Elon Musk himself confirmed it some time ago, and there are some fan-made simulations that prove it.

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  • $\begingroup$ I'm not seeing the Flight Club link show up properly. It just takes me to the homepage. $\endgroup$ – Nathan Tuggy Jun 2 '17 at 20:19
  • $\begingroup$ Huh, weird. Must be something related to the website overhaul some time ago. Nothing I can do I'm afraid. In any way, it's just another simulation. I'll try to get it working tomorrow. Thanks for letting me know! $\endgroup$ – mariohm1311 Jun 2 '17 at 21:31
  • $\begingroup$ Very cool. Of course I asked this awhile ago when the answer was not so clear - and before the upgraded engines and the extra-cold fuel. At this point I think it will get done and demonstrated sometime. $\endgroup$ – Mike Wise Jun 3 '17 at 12:58

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