Replacing Orion SM fuel with Cryogenic fuels

[fredinno]

Would it be possible to replace Orion SM propellant from hypergol to a cryogenic propellant economically? Would boil-off be too much of a factor? Would it even be worth it?

Here are the Cryrogen fuels I am considering:

H2/LOX (possibly with electrolysis to produce fuel on demand)

CH4/LOX

RP-1/LOX

NO2/C2H2 (semi-hypergolic propellant with very little copling requirements, but non-toxic and similar ISP, could reduce costs)

[Kryten]

How do you handle RCS?

[fredinno]

How do you handle RCS?

Rcs is normal monopropellant used on tge actual Orion. The furl and RCS would be seperate tanks.

[SomeGuy12]

The reason for liquid, hypergolic fuels that stay liquid at ambient temperatures in orbit is that here's what your rocket engine looks like.

There's 2 tanks, one containing fuel, the other oxidizer. Both are pressurized with helium. There's a valve coming from each tank, with a servo motor on it. Both feed into a rocket nozzle.

You want to fire the engine? Send power to both valves. Turn it off? Cut the power, springs close the valves.

This is as simple as it can possibly be. Well, not quite, a single tank with a single valve is simpler (monopropellant) but there is less performance.

You can wait for years in between engine burns. You can lose power to the capsule and do the burn if you ever restore it. It's reliable and will get you home.

Sure, cryogenics have better performance, but the complexity is much greater. More complex tanks, there's a vacuum insulation layer that can fail, the valves have to be made of high quality material, and you need a cryocooler, heat radiator, and always on power source to keep the liquid cold. Or, you constantly lose propellant the longer you wait. That's a negative, no competent aerospace engineer is going to sign off on that.

[Kibble]

What would the point be? It would barely increase the delta vee, and cause all kinds of problems. Orbital spacecraft use hypergolic storable fuels for a reason!

[Streetwind]

It would probably decrease the dV, since you'll need tank walls several times the thickness, and active cryocoolers with radiator surfaces and coolant lines and all that mumbo-jumbo. It weighs a lot. There's a reason nobody has built spacecraft with cryocoolers so far - and that reason is: you get the same, if not more, dV using storable propellants due to dry mass savings.

[Nibb31]

Rcs is normal monopropellant used on tge actual Orion. The furl and RCS would be seperate tanks.

Orion uses the same hypergolic propellants for the RCS, the main engine and the 8 auxiliary engines, all fed from the same tanks.