> fuel sloshing around is really hard
Can't the fuel be stabilized mechanically, e.g. as in a syringe?
Can't the fuel be stabilized mechanically, e.g. as in a syringe?
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.
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.
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.
Think a radiator, lots of tiny fins, but all inward pointing in a tube. Coat the fins so they are '-philic' to the liquid. Get creative with the geometries of the fins. Surface tension / capillary-action spread over a lot of the fins in the tube will move the liquid to a sink, like the combustion chamber.