Support the shaft and separate fuel from oxidiser. The inter-propellant seal is the critical safety item.
What decides the purchase: DN value · axial and radial load · operating temperature · leakage rate
Typical materials: Silicon nitride hybrid bearings, carbon face seals, PTFE and polyimide
Typical processes: Precision grinding, lapping
What changes when it has to fly: Cryogenic bearings usually run propellant-cooled with no conventional lubricant. Dry-film lubrication only.
Engineering reference written by us, not a supplier claim.