Air-augmented Rocket

[shynung]

I've recently come across this interesting concept on a poorly-cited Wikipedia page: https://en.wikipedia.org/wiki/Air-augmented_rocket

Basically, it describes a type of rocket that collects additional reaction mass in the form of ambient air whenever in an atmosphere, mixes it with exhaust from the rocket nozzle while not necessarily combusting it, and exhausts this mixture through another nozzle.

Possible advantages from this design would be increased I_SP and/or thrust compared to a conventional rocket in atmospheric conditions, flexibility to work with virtually any type of fuel (even solid fuels), and the relative simplicity compared to designs such as SABRE. Disadvantages would be no increase in I_SP and/or thrust at zero airspeed, slightly lowered TWR due to the air duct's weight (though they could be discarded once out of the atmosphere), and maybe cooling problems.

I'd like your opinions on the feasibility, expected gains and losses, and possibility of this design actually flying in the near future.

BTW, here's one company's take on it: http://www.sei.aero/eng/papers/uploads/archive/SEI_SCAAT-2013_PublicBrief.pdf

No intentions to advertise, but their launch vehicle looks really cool.

[Starwhip]

Hmm. Well, it seems possible, but it would probably be very expensive. Let alone the fact that the Skylon aircraft/rocket is already being planned and/or built.

[shynung]

While that particular company's approach may be expensive (reusable launchers are the trend nowadays), the concept is actually really simple. The only thing a rocket engine needs to be air-augmented would be installing some sort of shroud around the engine that has an intake scoop. That's it.

[Nuke]

looks like a poor mans skylon. the first stage only gets you to the edge of space and around mach 2 (so it doesn't do a hot re-enter), but is completely reusable. after which you require an expendable booster for the rest of the orbital insertion. this looks like a reasonable cost reducing approach to putting things into space. its not as sexy as skylon, but it is a good intermediate design.

and they painted it black so im all in, any space plane can fly if you paint it black.

[KASASpace]

Wait, is this essentially a nuclear ramjet minus the nuclear reactor plus the rocket engine?

If so, you could get extra thrust, but no necessarily more Isp, probably less total Dv. That's because of the equation used to calculate multiple Isp's. It's complicated, but you would get less D-v in your rocket. Might not be a good idea. Unless you had a horrible rocket Isp, then it could improve chances.

[Sauron]

There was a stab at this in the mid 60s (http://www.astronautix.com/lvs/gnom.htm). Very exciting performance. The great thing about air-augmented rockets is that they're dead simple compared to (say) a SABRE (with that nightmare of a precooler) in that you're just using air as extra working mass for a regular rocket engine in addition what you get with your fuel and oxidizer.

Note that with solid rockets you can double ISP from ~250 to ~500 in atmosphere. You're carrying more structure, mind, but at a certain point this could probably be offset.

Edited February 16, 2014 by Sauron