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Does any rocket engine combine air-breathing and non-air-breathing modes?

The advantage would be it would have to carry a smaller tank and less oxygen, leaving more room for payload on a weight basis.

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    $\begingroup$ Yes. $\endgroup$
    – Sanchises
    Commented Mar 2, 2020 at 11:44
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    $\begingroup$ @Sanchises the SABRE is still in development. $\endgroup$
    – Manu H
    Commented Mar 2, 2020 at 15:03
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    $\begingroup$ @securitydude5 by definition, rocket engine is not air breathing. You should speak of jet engine. $\endgroup$
    – Manu H
    Commented Mar 2, 2020 at 15:04
  • $\begingroup$ @ManuH SABRE is described as an air-breathing rocket. That is exactly how its engine functions in airbreathing mode. It has no fans or through-duct, what it has is a rocket chamber fed by fuel and oxidant. $\endgroup$ Commented Mar 4, 2020 at 19:21
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    $\begingroup$ I fail to see why this question is closed. Yes it is an overlap between space.SE and aviation.SE. Aircrafts with rocket engines exist (e.g. the Me163), thus rocket engines are on topic here. Why can't our community accept overlaps? $\endgroup$
    – Manu H
    Commented Mar 5, 2020 at 6:10

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There's a very recent claim for an engine called Fenris, which claims to be a no-moving-parts "rocket" that uses ambient air for its oxidizer.

On the face, that sounds like a ramjet, but the claims made by the inventors appear (to me) to be investor bait, rather than anything that could actually be true. Video on the entry page at the inventor's web site shows a burn more like that of a poorly designed torch, than a rocket or jet.

As noted in comments, there is also the SABRE engine concept -- this is not yet a working engine, as far as I know, but will/would be a hydrogen-fueled turbo-ramjet which uses the liquid hydrogen to liquefy intake air while in jet mod, for use as oxidizer when it switches to rocket mode. The intent is for use as a spaceplane-to-orbit.

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  • $\begingroup$ A no moving parts rocket that uses ambient air, it sounds like a ramjet. $\endgroup$
    – Manu H
    Commented Mar 2, 2020 at 15:09
  • $\begingroup$ @ManuH Go look up the Fenris "rocket" -- their claims aren't calling it a ramjet, and they seem to think they can convince investors it'll work. Physically, the engine they have looks much like a rocket thrust chamber and nozzle. $\endgroup$
    – Zeiss Ikon
    Commented Mar 2, 2020 at 16:52
  • $\begingroup$ SABRE uses liquid helium to cool the air to near (just above) its liquefaction point. This is then turbo-compressed and fed as oxidant to a conventional hydrogen-fuelled rocket chamber. The intent is to first find sub-orbital applications, with orbital flight being a longer-term aspiration. Currently the individual engine subsystems have all been bench-tested, notably the pre-cooler, and development of a flight demonstrator is starting. $\endgroup$ Commented Mar 5, 2020 at 12:37
  • $\begingroup$ @GuyInchbald Been a while since I looked at the SABRE. Now they want to carry a second cryogenic liquid? One they don't even burn off, so have to carry all the way? Seems like trying to save a concept that didn't work as expected... $\endgroup$
    – Zeiss Ikon
    Commented Mar 5, 2020 at 13:07
  • $\begingroup$ @ZeissIkon The helium intermediary has been in the design for a long time now. It has a complex thermodynamic function in utilising the waste heat to help drive the rest of the system. More like making practical a concept that was not quite figured out in the early days. There are other significant changes too, but design details seem scarcer than they used to be. $\endgroup$ Commented Mar 5, 2020 at 14:04

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