Attitude Control of All-Electric Satellites During Low- Thrust Orbit Transfers

Abstract

Attitude control of spacecraft during low-thrust orbit-raising maneuvers poses a problem for the adoption of electric primary propulsion systems in telecommunications satellites due to the potentially large slew requirements associated with the long duration of the continuous-thrust maneuver over which the spacecraft must maintain a target attitude. For the entire duration of a transfer trajectory, which may take several months for a transfer from LEO to GEO, an all-electric spacecraft must maintain its primary thrusters pointed along a specified target direction as well as keep its solar arrays oriented to the sun for power generation. In this study, a model for the attitude dynamics and control of a spacecraft using reaction wheel actuators is developed in order to investigate the attitude control system requirements to maintain pointing along an orbit-raising trajectory. Attitude control is then simulated for three orbit-raising scenarios in which maneuvers are the solutions of minimum-time low-thrust trajectory optimization for an equatorial, polar, and three-dimensional transfer to GEO. Results from these three case studies show that for an all-electric equivalent to a typical geostationary telecommunications satellite, the spacecraft is able to maintain thrust direction and orient its solar arrays normal to the sun for maximum power generation for the entire transfer duration without exceeding maximum reaction wheel control torques or requiring momentum unloading maneuvers to spin down reaction wheels. Moreover, the simulations predict the reaction wheel power consumption remains very small relative to the spacecraft power budget during the transfer. These conclusions demonstrate predicted attitude control system requirements for low-thrust missions to GEO, with the aim to incorporate rotational dynamics into complete six degree of freedom trajectory optimizations for all-electric spacecraft in future work.