Fun SpaceX Paper and Presentation

I just saw two interesting SpaceX documents linked to on NASASpaceflight.com. The first is a paper that was presented at the Fourth Asian Space Conference back in October, and the second is a presentation from the von Braun Symposium, also back in October They’re both fairly interesting, and provide some extra insight into the direction SpaceX is looking at pursuing over the coming years. I wanted to post them here for you all to read and comment on.

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13 Responses to Fun SpaceX Paper and Presentation

  1. corrodedNut says:

    The first thing that struck me about this paper is the the Merlin1c vacuum config is throttleable from “60 to 100 percent”, but apparently they decided not to make the first stage Merlins so, or else, why the staggered shut down? Why not make all Merlin 1c’s throttleable? Is it much more expensive to do so?

  2. Jonathan Goff says:

    corrodedNut,
    I can only guess, but one possibility is that staging might be at a low enough altitude that they lose more performance by throttling down than they would at higher altitudes where the upper stage operates?

    ~Jon

  3. Robert Horning says:

    I’m curious…. why would you want to throttle engines on the first stage?

    The usual reason for adding throttle control is to modify the acceleration rate, as towards the end of the burn you will find that stage hitting its maximum acceleration. Things like nuclear warheads don’t care if they hit 25 “g’s”, but passengers tend to have a few problems with that sort of stress load, not to mention that you may be hitting safe engineering limits on the structure of the vehicle.

    I can only assume that the rate of acceleration as the Falcon rockets approach MECO is within reasonable limits, removing the need for such mechanisms. It also fits with the viewpoint that SpaceX has to make things as cheap as they can safely be made, as throttle controls add extra weight and complexity… two things never viewed as positive for rockets.

    Apparently the Falcon 9 is going to achieve throttling by simply shutting off engines towards the end of the stage burn… doing essentially the same thing but through a process that doesn’t require engine-specific throttling capabilities.

  4. Frediiiie says:

    Musk said in comments after falcon1 launch 2 where the first stage impacted the nozzle of the 2nd stage during seperation that one of the fixes they could apply was to reduce thrust before engine cut off. but the cost would be “some loss of engine life”.
    If you plan to recover and reuse your engines throttling evidently becomes an issue.

  5. Frediiiie says:

    Another point from the above documents is that the merlin 1c on the Falcon 1 is currently being run at less than full throttle as the current falcon 1 structure is not rated to cope with the maximum thrust the merlin can produce.
    The merlin 1c will be openned to full throttle with the Falcon 1e
    It seems that there’s more to adjusting the thrust than just spinning the turbo pump faster or slower.
    In the interests of keeping their engine simple (and costs down) they’ve opted to keep the thrust constant and just shut 2 engines down late in the falcon 9 flight.

  6. corrodedNut says:

    Hey guys-
    If you look closely at Fig. 9 of the Asian Space Conference paper, around the perimeter of the fuel tank bottom edge, do you see what appears to be two or more Draco hypergol thrusters? I have read that the Falcon9 2nd stage will use Draco’s for on-orbit manuvering, these seem especially well positioned for performing a de-orbit burn. The Falcon9 2nd stage is shaping up to be a quite a little spacecraft in its own right. Also, what are the flat black panels around the bottom dome for, and could the snub nosed shaped structure at the front be some kind of heat shield?

  7. Jonathan Goff says:

    cN,
    Good catch. It does look like there are a few Draco thrusters there. The nosecone on the front definitely looks like a reentry shield, which means my guess for those black panels is that they are aerodynamic surfaces of some sort. Basically flaps/drag flaps that make sure the vehicle stays pointed in the right direction during reentry. I could be wrong, but that’s my guess.

    Overall though, it looks like a pretty interesting stage. I have a lot more confidence that it’ll be recoverable. Although IMO, a Mid Air Recovery option or a powered landing option (possibly a horizontal landing option?) would increase the odds of getting the thing back in one piece.

    One thing it does look like though is that this stage would not be as good of a stage to use as a base for a reusable deep-space transfer vehicle. Way too many things poking into the LOX tank. That’s ok though. I’m sure Elon would cry all the way to the bank if ULA made a Centaur based transfer vehicle, and Elon was “stuck” just selling the propellant, cargo, and crew delivery….

    ~Jon

  8. Joe says:

    The size of the bottom of the pressured structure seems to be the same as the top. It looks like the dragon capsule was designed with the notion of maybe putting a CBM at the bottom of the capsule? I wonder if there might be a notion of a expanded MOL like payload for a Falcon9 heavy.

  9. Paul Breed says:

    Why not throttle the 1C?
    whenever you throttle an engine you loose performance, IE ISP.
    So if I can reduce thrust by throttling 9 engines all loosing ISP, or I can reduce thrust by shutting down 2, with the remaining 7 running at
    full throttle and full ISP it makes more sense to shut down two.

    With the 2nd stage there is only one engine so to reduce peak g loads one needs to throttle.
    .

  10. corrodedNut says:

    I see now that there are plenty of good reasons why not to throttle an engine. I wonder if SpaceX is considering using a throttleable 1c on the improved Falcon1e to produce a more benign staging event, or is it better to just leave the Falcon1 well enough alone?

  11. Eric Collins says:

    Just a few random thoughts.

    Regarding throttling the Merlin 1C and the comment about reduced engine life; perhaps when the engine is throttled down, the regenerative cooling is no longer sufficient to prevent excessive heating of the thrust chamber and nozzle. Thus, increased wear and tear could prevent as much reuse as they would like.

    If the panels are control surfaces as Jon suggests, then the can be used to control the orientation of the vehicle which affects both its lift and drag. In this way, a stage or capsule may be actively flown (or at least falling with style) within a narrow corridor for a more precise touchdown/splashdown.

    I’ve often wondered about the shape of the Dragon pressure vessel. It certainly seems as if it would be possible to have docking rings at both ends; assuming of course that you can design a hatch and TPS that can withstand the heat of reentry. But what would be the purpose of the dual hatches? Maybe the Block 2 Falcon 9 or Falcon 9 Heavy will also be capable of launching a service module for extended duration missions. With a service module attached to one end, and a lander attached to the other, could Dragon possibly be upgraded to fly lunar missions?

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  13. Mike Puckett says:

    “Apparently the Falcon 9 is going to achieve throttling by simply shutting off engines towards the end of the stage burn… doing essentially the same thing but through a process that doesn’t require engine-specific throttling capabilities.”

    This is also the way it was done on the Saturn IC and II stages to limit G-loading.

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