Author Topic: Hypergolic fuel for Starship (Read 3827 times)

Anguy · « **on:** 12/03/2022 11:22 pm »

What do you think about this idea? I know it is against SpaceX philosophy and requires the development of new engine, but it has also several advantages, at least for deep space/Mars starships.

Hypergolic engines are relatively simple and reliable. Also special landing engines could be than developed, that are more throttleable for example, allowing for better control when landing.

Hydrazine can also be used by maneuvering thrusters.

Boil off is not a problem, allowing for longer missions, lighter and simpler fuel tanks.

Unlike cryogenic fuels, hypergols can be used as antiradiation shielding. This is the biggest advantage, IMO. Cryo fuels need to be located in single heavily insulated place like nose of the ship currently, so they cant be used as shield very efficiently. Hydrazine/and N2O4 tanks could be located in/around the outer walls of the crew section. 30-40 tons of of fuel would create pretty decent (and big) shelter. And because you need to carry it all the way to your destination anyway, it is a shield for the whole voyage without penalty to other useful payload.

Freeing the very tip of the nose could theoretically allow nose docking and more easily connecting 2 ships for spin gravity if necessary. Potential emergency escape capsule for crew during LEO missions can theoretically also be carried ON the nose during ascent. The important weight balance of the starship during descent doesn't change very much, because landing fuel is still there, just located little lower.

ISP is lower than for Raptors (300+), but for landing engines it doesn't matter that much.
I'm not sure how complicated it is to manufacture N2H4 and N2O4 on Mars but necessary elements are there and you don't need that much of it...

AC in NC · « **Reply #1 on:** 12/04/2022 02:10 am »

Quote from: Anguy on 12/03/2022 11:22 pm

What do you think about this idea?

Meets ZERO requirements. Total non-starter.

chopsticks · « **Reply #2 on:** 12/04/2022 04:57 am »

Not going to happen unless they can find hydrozene on Mars.

The only place I can see hypergols being used on starship is some sort of an abort system, but even that is far from certain.

Maybe (but very unlikely IMO) lunar landing engines as well.

Hamish.Student · « **Reply #3 on:** 12/04/2022 06:33 am »

Quote from: chopsticks on 12/04/2022 04:57 am

Not going to happen unless they can find hydrozene on Mars.

Hydrazine is N2H4. Both components can be found/made on Mars. It wouldn't be impossible to ISRU Hydrazine.

http://pages.erau.edu/~andrewsa/sci_fi_projects_fall_2018/Project_3/Marseglia_Dom/The_Martian_Project_Domenic_Marseglia/The_Martian_Project_Domenic_Marseglia.html

ETA: Not to say I agree with the premise of the thread, just wanted to refute the idea that Hydrazine on Mars is impossible. I agree with the points raised by sebk.

sebk · « **Reply #4 on:** 12/04/2022 12:46 pm »

The whole idea one big non starter. It's good for Pythom Space not SpaceX.

Hypergolic engines are simple when they are pressure fed. Pressure fed engines mean heavy tanks.

If you want low pressure tanks you need pumps and your simplicity gain is mostly gone.

Leaks are a big problem. Leaked stuff tends to freeze rather than evaporate, and that comes with whole lotta associated trouble. Leaks of the oxidizer are even bigger problem as this crap is badly aggressive. Using either as a cabin confroming radiation shield is a no-no because of those issues.

Hypergolics are expensive. Expensive enough for it to actually matter. Fully loading Starship tanks (without super heavy) would be from $17M to $100M. The later is at the current price NASA pays, the former is assuming bulk discuonts.

Ground handling of standard hypergolics is prohibitive, making high flight rate impossible.

edzieba · « **Reply #5 on:** 12/05/2022 11:00 am »

Even the Soviet Union baulked at building hypergolic launchers larger than Proton, and you'd be looking at a UR-900 scale flying superfund site to vaguely approximate Starship's capabilities.

Anguy · « **Reply #6 on:** 12/06/2022 06:15 pm »

I was talking only about landing engines and header tanks. That means only about 30-40tons of prop per Starship. Main engines and tanks would remain Methalox...
For Near Earth Starship it would't be worth it. For Mars and Deep space missions it might. For example I doubt you could make a manned mission to near Earth asteroid or belt purely with cryofuls.
I guess it also depends on how big a problem radiation will be... If too serious, mission planners would be very glad to have fuel usable as shielding...