Electric Propulsion and Controller Design for Drag-Free Spacecraft Operation

A study is presented detailing the simulation of a drag-free follow-up mission to NASA’s Gravity Recovery and Climate Experiment. This work evaluates controller performance, as well as thrust, power, and propellant mass requirements for drag-free spacecraft operation at orbital altitudes of 160–225 km. In addition, sensitivities to thermospheric wind, Global Positioning System signal accuracy, and availability of ephemeris data are studied. Thruster (control actuator) models are based on two different Hall thrusters for providing the orbital along-track acceleration, colloid thrusters for the normal acceleration, and a miniature xenon ion thruster for the cross-track acceleration. At an altitude of 160 km, the maximum along-track thrust component is calculated to be 98 mNwith a required dynamic (throttling) response of 42 mN=s. Themaximum position error at this altitude was shown to be in the along-track direction with a magnitude of 3314.9 nm. At 225 km, the maximum along-track thrust component reduces to 10.3 mN. The maximum dynamic response at this altitude is 4:0 mN=s. For the spacecraft point design considered with a propellant mass fraction of 0.18, the mission lifetime for the 160 km case was calculated to be 0.76 years. This increases 2.27 years at an altitude of 225 km.