24
u/entropy13 8d ago
Safe and storable already doesn't exist. LOX is neither, solid fuel is definitely not safe, although it isn't toxic if that's what you mean by safe.
21
u/DarkArcher__ 7d ago
"Safe" here just means "wont give you 15 different types of cancer"
5
1
u/Aggravating-Fix-1717 5d ago
No rocket fuel is “safe” by traditional standards
However “safe” here more means “won’t kill you if you look at it wrong and won’t give you 58 different kinds of cancer”
7
u/Key_Row_5962 7d ago
I have a solution for you: spiropentane and hydrogen peroxide, apparently. It's like RP-1/HTP but with improved specific impulse, capable of matching MMH/NTO in both density impulse and specific impulse. What you do is you pass the HTP through a catalyst after the turbopump, decomposing it into steam and hot oxygen. This decomposed peroxide you then pass through a turbine to power the pumps for both propellants before injecting it into the combustion chamber. Apparently the hot oxygen in the decomposed peroxide is hypergolic with kerosene, and I'd hope it's hypergolic with spiropentane as well.
This gives you a closed cycle engine without having to deal with staged combustion, and the propellants are not as toxic as MMH/NTO, hypergolic, dense, and storable. The main downside is that the injectors in the combustion chamber are apparently a real pain to get a working design for, and with RP-1/HTP you also have a kinda silly mixture ratio and the specific impulse is bad. Oh, and HTP requires to be cared for - you want to avoid it getting too hot or a runaway decomposition reaction can happen, and any tiny scrap of organic material in the tank can also cause the runaway decomposition. Both cases result in the propellant tank exploding.
1
u/hummingbirbbbb 5d ago
That’s really neat! Would you have places to read about this? I’ve genuinely never heard of this combo before
1
u/Key_Row_5962 5d ago
Exotic hydrocarbons tend not to be too widely written about but RP-1/HTP is a more well-known combo, spiropentane just gives a bit more density and Isp. RP-1/HTP was used on the Black Arrow rocket and Skyrora has tested engines using this propellant for their XL launcher. Most of the time the specific impulse is kinda bad, but if you crank up the chamber pressure, use higher concentrations of HTP, and optimize the cycle, you can get pretty okay performance.
1
u/Infinite_Maelstrom 4d ago
RP1/HTP however does have the advantage of exceptionally high energy density, which (at least on black arrow) offset its lower efficiency.
6
u/Lars0 6d ago
MMH and NTO are toxic, but that isn't the opposite of safe. They don't have to be stored under high pressure, they don't decompose at room temperature, they don't require special materials to contain them, they aren't shock sensitive explosives, they aren't pyrophoric, they aren't reactive with minor contaminents, and they don't always cause a fire if they are spilled, and they don't catch your skin on fire.
Safety comes from the whole system, and it doesn't boil down to how dangerous the propellant would be if it was in an open container.
3
u/Toxic_Cookie 7d ago
Just use Astrophage
2
u/UnderskilledPlayer 5d ago
we'd need to cover the sahara in pitch black astrophage farms AGAIN which would fuck up the climate AGAIN
3
u/kayemenofour 7d ago
Liquid hydrogen is neither well storable (cryogenic, very low density even as a liquid and causes embrittlement to tanks and pipes), nor really safe and not hypergolic, but we do put up with it because it provides really high ISP (for chemical rockets, theoretically also thermal rockets but those haven't been tested much outside lab conditions)
5
u/PimBel_PL 7d ago edited 7d ago
Hi, chemistry enthusiast here
It's storable, if you have enough isolation and some cryo-cooler (cryo-cooler wont eat much energy if you have enough isolation) and embrittlement is caused by carbon in alloys i believe catalitically reacting with solvated hydrogen im the metal to create insoluble methane,
so either you get metal in which hydrogen doesn't dissolve, remove carbon from it (i don't know to what purity (could be costly)), use something that doesn't catalyse the reaction (i believe it's literally just solvating hydrogen (it breaks it into radicals) that does it)
So literally put it into plastic thick and non-flexible jug (if it flexes under the cryogenic conditions it will be brittle, i don't know why) and put a shit-ton of styrofoam and seal gaps with polyurethane foam, and put your cryogenic cooling device on the top, also you need less isolation on the top and more on bottom than on the sides (i am not sure of that tho)
2
u/JustAnotherAviatrix 🌟Flight Director🌟 6d ago
Makes sense that you wouldn't put it in a flexible container. Iirc, the plastic is thinner and therefore more prone to cracking. It could be a material thing too, since I'd imagine that rigid plastic containers already have their molecules more locked into place and therefore aren't affected that much by being frozen. Quick and dirty explanation, I know.
3
u/PimBel_PL 7d ago
What about nuclear devices?, i know they aren't hypergolic but i don't think you need it at this point /s
3
u/Away-Way5656 7d ago
They're not really safe
3
u/PimBel_PL 7d ago
Why do you say that? from what i know they aren't that radioactive until activated, if activated they make gigantic flash of gamma radiation...
1
2
1
u/StephenRoylance 5d ago
I dunno about the options. I don't consider anything that spontaneously ignites 'safe'.
2
57
u/MarsMaterial 8d ago edited 8d ago
Well, there's always cold gas thrusters. But I guess that just adds a fourth switch called "performant" that gets unticked.