Intakes For Descent... Viable?

[Spacescifi]

 

So as I watch SpaceX land reusuable booster rockets, it got me thinking... what if they added intakes?

I mean if you take a spacecraft let descend during reentry, and as soon as it reaches below supersonic speed you open intakes at the rear, flip over so the rocket's nozzle is facing the ground and start firing the rocket motor exhaust.

Meanwhile the intakes suck up air as the rocket IS falling downward.

Would that save on landing propellant at all?

Or would the extra intake and compressor weight make it no better than s normal reusuable booostsr?

Since the extra weight cancels out the fuel savings?

Would it work better with a nuclear reactor?

 

Edited April 21, 2020 by Spacescifi

[RealKerbal3x]

Air intakes wouldn't really produce any appreciable thrust - they're designed to accelerate very light air through a jet engine, not the other way around. Adding intakes would just add a bunch of extra mass for little to no extra thrust.

Plus, what are you going to do with all this air you've sucked into your reusable booster? You can't vent it, because that would probably have the opposite effect to sucking it in in the first place; and you can't use it as oxidiser (at least not with conventional rocket engines) because rocket motors need purified liquid oxygen, and air has a bunch of other gases in it.

You might be able to use a nuclear reactor to superheat air harvested by these intakes and use that as reaction mass, but I'm not sure how much thrust that would produce.

Edited April 21, 2020 by RealKerbal3x

[Spacescifi]

15 minutes ago, RealKerbal3x said:

Air intakes wouldn't really produce any appreciable thrust - they're designed to accelerate very light air through a jet engine, not the other way around. Adding intakes would just add a bunch of extra mass for little to no extra thrust.

Plus, what are you going to do with all this air you've sucked into your reusable booster? You can't vent it, because that would probably have the opposite effect to sucking it in in the first place; and you can't use it as oxidiser (at least not with conventional rocket engines) because rocket motors need purified liquid oxygen, and air has a bunch of other gases in it.

You might be able to use a nuclear reactor to superheat air harvested by these intakes and use that as reaction mass, but I'm not sure how much thrust that would produce.

 

Think of it as a spacecraft that uses traditional staging to reach orbit but then uses airbreathing turbofan or turbojet (whichever is more efficient) rockets for for descent and landing.

Propellant is still used, but the whole point is to be able to do more with less propellant.

[Guest]

Actually, air is heavy, so if you've got a nuclear rocket designed for it, you can probably land for free, and get a good portion of liftoff for free, too. A simpler tech is an air-augmented NTR, which would still need normal propellant, but use air intakes to increase thrust when in certain speed regimes. This type of rocket would likely need some assistance on landing (wings, parachutes, or LOX injection), but it could end up lighter in general.

Jet engines on rockets add too much mass. Russians have experimented with winged boosters, but nothing came of this. They would have had jet engines.

[Meecrob]

The beauty of a brayton-cycle gas turbine is that there is continuous combustion. This lends itself particularly well to applications you currently see gas turbines being used in - none of those applications are 0-100% bursts of thrust 3 times within 8 minutes for durations of less than 15 seconds each burn. They invented rockets for those applications...look at JATO from the 50's/60's.

[RCgothic]

Jet engines don't really work very well thrusting into the oncoming airstream.

[kerbiloid]

If the intakes are enough wide, we can use them as chutes.

[Nightside]

Why mess around with intakes and fussy turbines when you can just go straight for a propeller?

https://en.wikipedia.org/wiki/Rotary_Rocket

 

Edited April 24, 2020 by Nightside
more manley

[Spacescifi]

27 minutes ago, Nightside said:

Why mess around with intakes and fussy turbines when you can just go straight for a propeller?

https://en.wikipedia.org/wiki/Rotary_Rocket

 

 

Yeah you have a point. The longer the rocket the longer the blades. Just unfold them and you should bs good to go.

Will need to a long, long, rocket the heavier the spacecraft is though to generate the have the needed length/thrust from the blades.

[kerbiloid]

Such high H:D ratio means almost ballistic reentry at ~10 g overloads.

Edited April 25, 2020 by kerbiloid