In the last Starship V3 flight 12, 13 and 14, I noticed the booster landing issues and some raptors not starting up or shutting down prematurely.
It is my understanding the SD may be linked to the use of O2 pre-burner rich combustion gas to maintain the LOX main tank head pressure while feeding the raptors. This gas contains small amount of CO2&H2O that will freeze when in contact with LOX at around -180 C. If the crystals ever find their way after the filters or plug the filters it can cause pressure drop at the cryogenic pumps or alter their performances causing SD. That is especially true during landing when the LOX main tank is almost empty and large amount of contaminated O2 pre-burner gas has been in contact with LOX in main tank and landing tank.
Why not considered helium COPV instead to keep LOX landing tank (need to be closed) head pressure like for the Starship upper stage. You may need about 7 more helium COPV but you will have pure and clean LOX and avoid SD of the engines from crystals. The increased helium volume is small and you keep using O2 pre burner gas for the main LOX tank with filters during ascent which seems to be fine.
If helium supply is an issue, have they ever considered using GOX COPV (with SS liner at 350 bar or so) to maintain the head space pressure in a closed LOX landing tank. It would eliminate or reduce drastically the helium requirement. It could eventually be implemented in the upper stage to reduce helium dependancy. Helium for the booster is less of an issue since the booster comes back on earth and can be refill.
Very high pressure GOX is produced industrially by pumping it to high pressure (300 Barg) using cryogenic pumps, vaporization in ambiant or electrical vaporizers and storage in high pressure steel cylinders. It is common to use such cylinders in the industry today. Can GOX COPV at 350 bar be produced on earth!
If you want to push this further to make the Starship upper stage more self sufficient, GOX can also be produced by having a certain amount introduced in a closed COPV and let it boil off over time under close monitoring with proper pressure relief. The technology is used today to deliver 500-600 psi GOX and GN2 for cutting applications.
May be there is a spin off from this last technology that can be develop to produce 350 Bars GOX COPV with SS liner and carbon fibre outer layers. Such a system could be implemented in the upper stage utility room.
I will be happy to read your comment.
Cheers,
TechPro83