Ram Air Compression

[JMBuilder]

Since part of the plan is an aerodynamics overhaul, I've come up with a new idea involving engine exhaust and air compression.

If a rocket engine is encased in some form of aerodynamic shell that allows air to flow through it, the air is compressed by the rocket exhaust, turning it into a ramrocket or air-augmented rocket. This would greatly increase a rocket's efficiency inside an atmosphere.

Perhaps a normal-sized shell part that could contain half-size parts could be added. This would allow ramrockets to be the same size as regular engines.

Or a ramrocket part could be added.

[NathanKell]

That's what the jets are, in KSP.

[JMBuilder]

Ramrockets work in any atmosphere. Jets don't.

[Red Iron Crown]

Air augmented rockets are interesting, though they'd really only be useful at Eve or Jool (Duna's atmo is too thin, on Laythe and Kerbin jets are better). It would likely be easier to make a dedicated engine for it rather than be able to air augment any engine. This could probably be simulated reasonably well just by messing with the Isp curve so that it's higher in atmo than vacuum.

[Kegereneku]

Ram air turbine it itself don't necessarily work in any atmosphere, not if the oxidizer you need to burn the Liquid fuel isn't present.

However as said above, an Air augmented rocket, can potentially use any source of compressed gas to increase it's thrust.

This is different from what the RAPIER engine do, so it would be a different engine.

Now, there is also the dream of nuclear jet engine which would work on any atmosphere (differently though).

Then again, if you don't mind "absolutely completely overpowered engine" there's also hypothetical plasma-engine with absurd power requirement.

[JMBuilder]

The ramrocket wouldn't necessarily be overpowered. It could have bad efficiency in the vacuum of space, nerfing it a bit.

[Kegereneku]

We could try to compare both concepts to see if one eat the other :

The RAPIER

Is basically a Turbojet that turn into rocket-mode

pro :

It does not use precious oxidizer until it lack air.

landing back you can reuse jet-mode to land cheaply

con :

Once in orbit you can have surplus mass of Liquid Fuel

Only work on Kerbin

The Ramrocket or air-augmented rocket

Is a rocket engine that have amplified thrust if used in any atmosphere

It use oxidizer anyway but require air-intake to gain extra thrust.

pro :

it give extra trust in any atmosphere

con :

is dead-weight outside atmosphere

Conclusion :

Please do not hesitate to give your own vision,

To me it seem we can balance a "RAMrocket" to be the "shuttle" of outer planet but it have to be VERY efficient.

I'm more worried about it shadowing other lift-off engine, especially the Aerospike (though it's because Isp isn't calculated as it should)

We can make it too costly to be expandable (or low thrust for high atmos Isp), but it is enough to not make it "OP" as a reusable SSTO ? Considering how easy it is to stack engine & parachute in KSP already I'm wondering if "Make launch 50% costly & require 90% recovery cost to brake even" would balanced it enough.

It still have to be a question of design choice after-all, if someone want to rely on this model he should be able to.

ps : Maybe each engine should have a "recovering rating" to allow better balancing of SSTO candidate ? Gotta make a thread about that.

[LethalDose]

Doesn't the Interstellar mod already have a part like this? I don't use the mod, but I think Scott Manley is using a similar part for an Eve spaceplane in his current series.

[Kegereneku]

Not exactly,

I'm following his Interstellar Quest and the shuttle that landed on Eve is an Air-augmented Fusion-engine

- In space it can work with fusion only, low thrust but supremely efficient.

- It can add stored reactive-mass to get a lot more thrust

- And in atmosphere it can add ambient air to the fusion to get high thrust at high efficiency

So basically it would be close the overpowered MHD "plasma-engine" I talked about first, but not the "RAMrocket" which is equivalent to other conventional LF/O rocket engine, except with added thrust in atmosphere.