tokens: The sizing process shall begin with a definition of the life phases of each element , including at least : 1 . Thrust level and range 2 . Total impulse 3 . Available power 4 . Mass budget 5 . Operating cycles 6 . Propellant , pressurant and leakage budgets 7 . Capacity of protections for sensitive components NOTE For example : oxygen absorbers for hollow cathodes . 8 . Accommodation envelop .