That's the big unsolved question. Easiest answer is that they are using preburner exhaust to pressurize the tanks, but putting CO₂, CO, water vapor and maybe a trace of unburned methane into an oxygen tank sounds like such a bad idea - but like you, I can't think of anything else that could block the filters.
robbak
joined 2 years ago
@jqubed @llamacoffee That's my opinion, too. Arianespace updated them with a further delayed launch date (commercially confidential). EUMETSAT decided to call SpaceX.