SpaceX Falcon 9 First Stage SSTO Simulation

Here is a simulation of the Falcon 9 first stage as a SSTO (Single Stage To Orbit) vehicle. There would be no practical reason for SpaceX to demonstrate this. However, I wanted to confirm the speculation that it could at least be theoretically possible. I try to keep the stress load on the rocket under 4.5Gs at all times by shutting down pairs of symmetric engines. This is a pretty aggressive flight profile, but I’m having trouble finding anything else that works. This barely makes it to LEO with a final orbit of around 180km x 170km.

The simulation software I wrote can be found on GitHub here:

If you just want to run the simulation here is a link to the program: .

  1. Could you do a simulation with the falcon Heavy but only the booster and first stage. No second stage or payload. I suspect it will get to orbit, but I wonder if the first stage could re-enter and land.

  2. Good work.
    Probably the first stage alone could go far away 4.5G, because, without the weight of the second stage and payload, the constraints on the structure of the first stage are lowered.

    Also, since the engines can be fired several times, there is, still with a max 4.5g, a far better profile, with much less gravity loss.

    Instead of shutting down 2 engines, only the central engine should be shut down, then re-ignited when 2 other engines are shut down.

    So, the sequence would be/

    1: All engines at max.
    2 : at 4.5G reached, Central Engine shut down.
    3 : When again 4.5G reached, 2 other engines shut down, and Central Engine re-ignited.
    4 : When again 4.5G reached, Central shut down again.
    5 : When again 4.5G reached, 2 other engines shud dows, and Central Engine re-ignited.

    You should get an higher orbit.

    Also, each Engine has an adjustable orientation, so you probably can shut down directly any engine, and orientate the others to get the thrust in the right direction. It is probably a better way to do it.

    The merlin 1.D has an adjustable thrust, from 70% to 100% So you can lower the thrust of an
    Engine before stopping it. But maybe it lowers the ISP. Does somebody know how much you lower the ISP by adjusting thrust to 70% on the Merlin 1.D ?

  3. Thanks for that. Great job. A SSTO gets best performance when using altitude compensating nozzles. With it, the F9 first stage vacuum Isp can be raised from the 311 s it is now to the 342 s Isp of the F9 second stage.
    How much would the payload be then?

    Bob Clark

  4. I can see you were running with very small margins there. The orbit also shouldn't be stable for very long. But I'm curious, what was the lowest angle that the ssts was pitched relative to the horizon? And another question, were you pulling any angle off in azimuth so as to be in an inclined orbit? I don't think the delta v values agree with your simulation for an equatorial orbit.

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