https://www.aerospaceprojectsreview.com/blog/?p=1325 In relation the the Boeing "Big Onion" SSTO LV, I was doing some brief digging on it's flight profile. (See the awesome Hazegrayart animation of the same name.)

It seems the atmospheric jets were only used on take-off, not on the landing or descent, instead relying on it's LH2/LOX engines. Would this be because of the lower thrust of the atmospheric engines, or maybe the difficulty of restarting the engines on descent, what with the intakes being upward-facing...

Anyway, all help on this question is appreciated.

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    $\begingroup$ There's no evident air intakes in the link. It looks more like there's a mix of kerolox and hydrolox engines. If my guess is correct, that's done as a mix of high specific-thrust engines and high specific-impulse engines. $\endgroup$
    – Erin Anne
    Aug 8 at 5:54
  • $\begingroup$ You are likely mixing Big Onion up with the Chrysler SERV, which did have jet engines. In the case of the SERV, they were specifically used for landing. $\endgroup$ Aug 8 at 14:45
  • $\begingroup$ Related: space.stackexchange.com/q/30215/6944 $\endgroup$ Aug 8 at 16:25
  • $\begingroup$ Ah, you are in fact right, cheers for the link too @ organicmarble $\endgroup$ Aug 9 at 6:18

1 Answer 1


Your question is based on a misunderstanding. That proposed vehicle did not utilize air-breathing engines.

Technical details can be found in the paper Future Space Transportation Systems Analysis Study on NTRS, along with other heavy-lift designs.

enter image description here

The landing aka auxiliary engines are described there as "LO2/hydrocarbon engines" and the booster engines as LH2/LO2 engines. Nothing airbreathing.

The kerolox "auxiliary engines" were to be used for the first part of ascent, the deorbit burn, and landing. The hydrolox "main engines" were to be used only for ascent.

The description starts on page 54 of the paper.


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