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Dragongeek t1_j6jr8yv wrote

Reply to comment by Bobandis458 in NASA tested new propulsion tech that could unlock new deep space travel possibilities by Creepy_Toe2680

iirc hydrogen-fueled air-breathing RDEs are theorized working up to Mach 5 at 8000-9000 isp and hydrocarbon fueled ones about half or a third that isp.

It's all theory though, but very attractive

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cjameshuff t1_j6k5pl3 wrote

Air-breathing engines aren't comparable to rocket engines. They have big specific impulse numbers because the specific impulse is no longer the impulse available from the propellant, but what's available from just the fuel after that fuel's been combined with the air. And since it's wildly variable with airspeed, it only makes sense for craft that cruise in a given range of airspeeds...in this case, Mach 5 and less.

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a10t2 t1_j6jw269 wrote

I haven't seen numbers anywhere near that. For a hydrolox RDRE they're hoping to hit maybe 550 s.

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