What is the highest Isp achieved on orbital rocket for an engine that used nitrous oxide as oxidizer? Both hybrid and liquid engines can be considered.

Not considering nitrous oxide monopropellant since it probably would perform the worst (is that true?).

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    $\begingroup$ I'm not aware of any orbital rockets or spacecraft that have used nitrous oxide in engines of any sort. Numerous sounding and amateur rockets, but nothing orbital. A few have planned to do so, but they've either switched to something else (Dreamchaser, for example) or have yet to fly. $\endgroup$ Commented Mar 24, 2021 at 23:42

1 Answer 1


I don't believe any orbital rockets use nitrous oxide as an oxidizer.

Zubrin claims it can be used with an ethelyne-ethane fuel blend to produce 320s specific impulse but that seems optimistic.

Wikipedia says it can be used in a catalyzed monopropellant thruster for around 180s.

N2O/ethanol has experimentally demonstrated 250s-260s.

SpaceShipOne/SpaceShipTwo fly a nitrous oxide hybrid rocket with HTPB solid fuel at 250s.

  • $\begingroup$ Looks like a pretty good Isp (250-260s) for a such simple single impinging injector in that N2O/ethanol engine (paper by Youngblood)? $\endgroup$
    – Kozuch
    Commented Apr 1, 2021 at 15:37
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    $\begingroup$ Hard to beat nitrous oxide diborane combination in terms of Isp. It gives well over 9MJ/kg of energy in respect to 6.5MJ/kg for nitrous oxide/ ethylene combination with practically the same average molar gas mass. Of course this combination is just of theoretical interest because diborane is highly toxic. Also nitrous oxide & hydrazine is superior to nitorus oxide ethylene in terms of Isp, but yet another highly toxic fuel. $\endgroup$
    – WOW 6EQUJ5
    Commented Apr 5, 2021 at 10:15
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    $\begingroup$ If I am a chief rocket designer and i receive task to design nitrous oxide orbital rocket i would try ethylene oxide as fuel. Why - higher density (if prechilled it reaches 0.95g/ml, much higher than ethylene-ethane), its mono-propellant so both fuel and oxidizer can be used to drive turbine, and full stage combustion cycle would be possible. Also it doesn't lag behind ethylene-ethane in terms of energy - 6.5MJ/kg. Fuel/oxydizer blends are also possible because both are liquids in same temperature ranges. $\endgroup$
    – WOW 6EQUJ5
    Commented Apr 5, 2021 at 10:38

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