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System impacts of propulsion Passivation

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Propulsion passivation is most of the time feasible for running missions, using thrusters and existing AOCS modes, whatever the number of tanks and for both monopropellant and bipropellant systems.
For monopropellant systems the propulsion passivation may be:
-Partial for tank(s) with membrane. All the hydrazine under the membrane may be depleted but the pressurant gas above the membrane cannot be depleted. The final tank pressure is close to typically 5 bars at the end of mission.
-Almost complete for tank(s) with PMD. All the hydrazine and the pressurant gas can be depleted. The minimum achieved final tank pressure was typically close to 2 bars.

For bipropellant systems with PMD tank, the propulsion passivation can be almost complete. Typical tank pressures at end of the propulsion passivation are less than 1 bar for oxidizer (NTO) and close to 0 for fuel (MMH). For propulsion systems with several pairs of oxidizer and fuel tanks, tank swap strategy is necessary to deplete as much as possible every tank. Asymmetry in the oxidizer and fuel quantities induces firing with monopropellant phase before reaching pressurant phase. Operation usually has to face thruster blockage due to propellant icing.

Executive summary