When reading On the Cusp: What’s NextDARPA Perspective on Space Briefing prepared for 53rd Robert H. Goddard Memorial Symposium March 12, 2015 I saw the slide shown below. The slide's heading is Notional X-Plane Upper Stage Trades and it mentions

Booster (2-Merlins):

  • Propellant = 176.5K lbs (LOX/RP)
  • ISP (vac) = 310 sec
  • PMF = 0.84

which does sound like a SpaceX Merlin 1D engine. I believe this is uses as simply a nominal engine spec for this notional, conceptual discussion.

But it made me wonder if there has been more serious discussion or tests involving the use of either SpaceX's engines or other private launch-providing liquid fuel engines on totally different vehicles.

I'm guessing there may be examples for solid rocket boosters being adapted in new ways since they are mostly self-contained, so the focus should probably be on the more complicated liquid propellant launch-enabling engines where the challenges are greater and the likelihood lower.

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    $\begingroup$ Are you only looking for commercial launchers? AJ-10 got used across Delta, Titan, Apollo, STS, Orion; Boeing considered RD-180 for liquid boosters to replace STS-SRB. $\endgroup$ Oct 30, 2018 at 16:09
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    $\begingroup$ @RussellBorogove sure! I'd said "or other private launch-providing liquid fuel engines" because I wasn't sure if I should say "private" or "commercial". Perhaps commercial is better. $\endgroup$
    – uhoh
    Oct 30, 2018 at 16:10

1 Answer 1


Not just discussion, this has been done multiple times. A non-exhaustive list:

  • Blue Origin's BE-4 will be used on ULA Vulcan as well as Blue Origin's New Glenn.
  • the Kuznetsov NK-33 was used on the Soviet N-1 launcher and on the Orbital Antares.
  • India used license-built Arianespace Vikings on some of their launchers.
  • $\begingroup$ Excellent; the notable exception being the Merlin, which I wound't expect to happen any time soon. $\endgroup$
    – uhoh
    Oct 30, 2018 at 7:11
  • $\begingroup$ I'm happy to see it back again, yay! Probably me too. After spending 45 minutes writing, looking up sources, calculating jumping heights and let forces and surface gravities, writing it all up, and finally clicking "Post your Answer" I saw someone posted a cartoon instead! I always have to remind myself to stop taking SE so seriously. $\endgroup$
    – uhoh
    Nov 1, 2018 at 11:12

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