Cryogenics

Cryogenics are very cold. The engine is very cold as it fires. The longer it is shut down, 
the warmer it becomes. The engine is typically hottest at the first start, but with longer 
coasts between starts it gets warmer.

Simulating loss by boiloff during coast:
1. O2 rich on first firing
2. Second burn - wait for things to stop sloshing

Cryogenic testing - test at cryogenic conditions
LH2 (-420) is dangerous - risk of combustion or detonation always exists

Use LN2 instead (-280) for safety. The idea is to give "cold shock" to the components.
The use of LN2 is not precise but close and safer.


Costs - cryogenic testing is expensive. H2 testing is very expensive. N2 is less expensive 
and therefore used.