Recovery From a Period of Missed Thrust During a Low-Thrust Mission to Jupiter

摘要

NASA's Deep Space 1 and the European Space Agency's SMART-1 have demonstrated the usefulness of using electric propulsion to enable large mass-fraction vehicles. For missions to the outer planets, a nuclear power source would allow both a constant power level for thrusting phases and provide relatively high power for the science instruments. Vehicles that fly along low-thrust trajectories may spend months or years in travel and generally require continuous thrusting during long durations of time in order to reach their destination. When a malfunction occurs that causes a total loss of propulsion during a period of planned thrust, a change from the baseline (nominal) trajectory is needed to enable the vehicle to still reach the target. The options available to recover the mission vary depending on the vehicle, its systems, at what point in the mission thrust is lost, and the length of time that thrust is lost. This analysis looked at several options to complete an Earth to Jupiter mission using nuclear electric propulsion, when a malfunction caused a total loss of propulsion for durations of 3, 7 or 14 days at various points in the mission. These options were: 1. Thrusting during any remaining (nominal) coast period 2. Increasing power to the electric propulsion system 3. Adjusting specific impulse 4. Adjusting arrival date 5. Combinations of the above methods with each other and/or with the use of more propellant If a recovery method could provide only a reduced end of mission mass, that change is quantified. The analysis looked at a representative heliocentric trajectory with a thrust arc followed by a coast arc, followed by a second thrust arc. The results of this analysis show that a loss of thrust during the first thrust arc is easily recoverable by using a small power margin, using more propellant while thrusting during the planned coast period, or allowing for a late arrival of not more than a couple of months. During the second thrust arc, recovery from a period of lost thrust is more difficult. The best recovery methods for a loss during the second thrust arc included a combination of late arrival and either an increase in P_0 or an increase in propellant usage or both.