Nuclear Sabre Engine

[Comrade Jenkens]

Would it be possible to combine a nuclear rocket with a sabre intake? This could allow a rocket to work in atmosphere like a jet engine while still getting a nice ISP in space.

[Aghanim]

Fortunately KSPI already have that, thermal turbojet with hybrid thermal rocket addon.

SABRE intake only works with cryogenic fuel to supercool the air into workable temperature, with nuclear jet engine doesn't need fuel, its easier and simpler to do SR-71 engine

compressor/bypass duct ramjet combo. The only thing that we need is a big valve to seal off the intake end so the injected propellant doesn't go to the wrong direction. I don't know how.

[Nuke]

both nuclear ramjets and ntr prototypes have been built and tested, and both proved viable. seems all you would need to do is change over from propellant to atmosphere as needed. this seems a simple matter of closing the intake and injecting lh2 into the engine when atmospheric operation becomes impossible. i have a feeling you wouldn't need a precooler though, besides you would need to spend hydrogen in air breathing mode to run the precollers, and you want to save that hydrogen for when there is nothing to intake.

then you got the problem where a ramjet doesnt work subsonic, or or past mach 3 or so. perhaps some kind of hybrid ram/scram configuration. still this isnt an engine you can launch from the ground. perhaps you can combine turbojet/ram/scram into a single nacelle and somehow fit a nuclear reactor in there as well. perhaps fit a single reactor into the fuselage and run heat exchangers to move thermal energy to the nacelles, which would be beneficial in a radiation containment capacity (it would be the coolant loop of the reactor, not exposed directly to the core but through a heat exchanger). you still wouldn't need a precooler, because the turbine would be isolated and shut down at around mach 1 when the ramjet takes over, heat is less of a problem with this type of engine.

i rather like the idea of a nuclear engine that can work surface to space purely on nuclear power (and without any regard to atmospheric composition). you can land at titan with the same engine you took off with from earth. it would certainly allow flexible spacecraft design. the other side of it is it sounds so complicated it probibly wouldnt ever work. not to mention you end up with a ship suboptimal for transfers (assuming space plane).

what about an air augmented nerva? same concept as an air augmented rocket, but with a nuclear engine providing the heat.

Edited April 13, 2014 by Nuke

[Elthy]

The USA developed a nuclear ramjet powered unmanned bomber in the cold war, see here.

[jfull]

The USA developed a nuclear ramjet powered unmanned bomber in the cold war, see here.

I was just about to say something about that. A nuclear ramjet and an NTR both operate on the same principles, so maybe it could be possible to combine their capabilities in a way similar to a Sabre engine?

It would run on atmosphere alone until that ran out, then switch to running liquid hydrogen over the reactor.

The only problem I can see is that, while using no fuel apart from the uranium in the reactor, a nuclear ramjet might not put out as much thrust as a chemical ramjet, or operate at as high an altitude.

Also, this really, really doesn't seem like the kind of engine that should be used on a manned flight.

[Comrade Jenkens]

I was thinking that rather than being a ramjet (which can only operate at high speed), it has a compressor at the front to force the air into the system just like a normal engine rather than letting speed force it in.

[KASASpace]

Well, why would you need an intake like the Sabres unless you wanted to cool it down, which does increase its density.

Perhaps it could get a slightly better Isp in atmosphere, but it wouldn't be extremely advantageous, because you get so little thrust......

[jfull]

Well, why would you need an intake like the Sabres unless you wanted to cool it down

You want an intake on it because a nuclear ramjet can produce thrust on nothing but incoming air and the heat of its reactor.

[KASASpace]

You want an intake on it because a nuclear ramjet can produce thrust on nothing but incoming air and the heat of its reactor.

A Sabre type intake.

I know the principle of the thing, heck, the Pluto missiles were going to use them, but is it really practical?

I mean, the thrust is going to be low because the heat transfer can only be done a few ways.

[magnemoe]

I was thinking that rather than being a ramjet (which can only operate at high speed), it has a compressor at the front to force the air into the system just like a normal engine rather than letting speed force it in.

Should be possible but would complicate it, Question is if it would be better to use it as an nerva to get up to speed instead, perhaps also some boosters

[bartekkru99]

I'm making a slideshow as my physics project about future of space exploration, largely inspired by KSPI (writing something about NERVA now) and I was curious if somebody else thought about combo of SABRE and nuclear engine, typed in google and as always the first result is KSP forum