Hybrid Fueled Rocket Engine (Solid fuel with liquid or compressed gaseous oxidizer)

[StevieC]

I was thinking something like the engine that propelled SpaceShipOne, which used HTPB rubber as the solid fuel, and compressed nitrous-oxide as the oxidizer. Would make a good engine for a final stage that circularizes the capsule's orbit, but also either retain enough delta-V to put the capsule on either a free-return trajectory 'round the Mün or Minmus, or simply to deorbit the capsule entirely.

[riocrokite]

There are currently no hybrid engines mod in KSP that I know of (maybe interstellar mod has some), also in real life hybrid engines are pretty much rare and recent development. Therefore you're pretty free to do whatever you like, for example duplicate 1.25m SRB model with liquid engine config (so you can change thrust level just like hybrid engines) + integrated solid resource, then you only need to prepare config for NO2 using suitable stock 1.25m tank and you're done  

One thing to consider would be that NO2 tank would be pretty long compared to the solid/engine part, similar to the picture below:

Edited March 13, 2016 by riocrokite

[FreeThinker]

Not yet, but I do have some plans to create some universal burner and universal oxigen engine. basisicly it's a reactor that produces energy from the chemical oxidasion which procudes a mixture of gas and waste  which can be used by the engine for propulsion. Should be usefull on moon where water is hard to find (like only in polar crasters). Just Converting Regolith tho metals you can bur is a whole lot easier. You just need a few Megawats of power, A nuclear reactor will come in handly.

Edited March 16, 2016 by FreeThinker

[wafflemoder]

SETI-BalanceMod adds a hybrid engine, which can also be found separately Hybrid Rocket Booster. 

[Wolf Baginski]

You could probably do all this in the part.cfg file.

Suggestion: use the Squad R-10 SRB with a fuel tank on top. It's a standard fuel-switch option to make the tank all-oxidiser, but you could make an edited version with the liquidfuel RESOURCE section removed, and names and description changed.

You also do an edited part.cfg for the SRB that adds a requirement for Oxidiser as a PROPELLANT. Check how the quantities and ratios work out. but then you start getting into the fine details of balance, I_sp, and the atmosphere curve.

The advantage is that you have a simpler mechanical system, only one set of pumps, but this would need a little more dead weight than an SRB. On the other hand, it's something you can stop and start.