3 ms·
In theory yes, and if worse comes to worse that is an option. But its not what any rocket designer would want to do. Having a mechanical system inside of a dee
by nickik 6y ago
In theory yes, and if worse comes to worse that is an option.
But its not what any rocket designer would want to do. Having a mechanical system inside of a deep cryo liquid methane is hugely complex and very heavy. Even if you put it outside, you still have deep cryo liquid inside and that would make it even heavier.
Consider that 1kg extra weight on the second stage reduces payload to orbit by 1kg and payload to Mars by much more overall.
- api 6y agoIs there some kind of material that remains elastic and strong at that temperature that could be used to create a bladder? I assume no, since that seems like something that would have already been done in place of helium pressurant if it were viable. All the rubbery or fabric-like things I know of that are stretchy like that become brittle at those temperatures.
- musingsole 6y agoNot your line of thinking, but I believe ferrofluids were developed to provide control over fuel in zero-g (i.e. a material that is elastic and strong, but that gets mixed with the fuel instead of encasing it)
- api 6y agoDoesn't it then get burned? Seems like it would deposit shit in the engine, which is bad especially for a reusable engine.
- musingsole 6y agoI believe it's meant to be fully filtered out of the fuel before burning (being magnetic, I think the filtering is a bit easier than some other non-reactive contaminate would be). Most of this is only half-recalled from someone's recent project that showed separating ferrofluid from some liquid on Earth...but I don't recall any other context :/
- nickik 6y agoI don't know if such a material exists. The problem is SpaceX operates with Deep Cryo fuel (only company that does so as far as I know). They are literally going to 66K on the LOX and methane. Helium was just temporary as well so once the actually design system is back with SN15 it should be better already. The idea that Starship has is to use the fuel and oxidizer in its gas form. So the methane tank contains liquid methane pressurized by gaseous methane. The benefit of this is that if the engine ingests some of that gaseous methane its less of an issue in terms of engine thrust compared to helium and its possible more recoverable of a situation.
- souprock 6y agoDo you mind if the material is only elastic and strong at that temperature? Suppose that perfluoroheptane is rubbery at those temperatures. (the melting point is -78 °C, which is 195 Kelvin, and SpaceX oxygen is kept at 66 Kelvin) It works for Mars rover tires too. Want rubbery tires? Use something like perfluoroheptane. Keep the vehicle cold during the trip, or mount the tires in disposable molds that wear away during use.
- amelius 6y agoHow about rotating the rocket so the fuel is pushed outward? The gyroscopic effect could also have a stabilizing effect on the rocket itself.