Optimal station keeping by electric propulsion in failure mode

The objective of this paper is to minimize fuel consumption used for station keeping for geostationary satellites by electric propulsion in failure mode. The Xenon Ion Propulsion System (XIPS), developed for Boeing 702 spacecraft, is used for electric propulsion. Two diagonal thruster pairs, each pair consisting of one north thruster and one south thruster, are mounted on the antinadir face of the satellite. In nominal mode, all four thrusters work for achieving control of longitude drift rate, eccentricity vector, and inclination vector, and the north thrusters fire at ∼90° right ascensions (RA) and the south thrusters fire at ∼270° RA. However, in failure mode, only one diagonal thruster pair fires. The original station-keeping failure mode strategy fires the remaining diagonal thrusters a second time, simultaneously, and with equal duration at ∼0° or ∼180° RA, in addition to a first time at ∼90° (north thruster) and ∼270° (south thruster), which leads to excessive fuel consumption for station keeping. A failure mode optimal station-keeping strategy with the firing locations and durations of one diagonal thruster pair as design variables is presented in this paper. Then, the optimal station keeping model is built with only one diagonal thruster pair, and applied for maintaining a geostationary satellite within a predefined space box. Numerical simulations show that an 11.3 % reduction of fuel consumption is achieved by the proposed optimal strategy.