Three-Axis Drag-Free Control and Drag Force Recovery of a Single-Thruster Small Satellite

A drag-free spacecraft uses a gravitational reference sensor to shield an internal free-floating test mass from all external disturbances and disturbances caused by the spacecraft itself. Since the test mass is completely freed from nongravitational disturbances, it and its "tender" spacecraft follow a pure geodesic. The next generation of drag-free space systems will provide autonomous precision orbit determination, more accurately map the static and time-varying components of the Earth's mass distribution, aid in the understanding of the fundamental force of gravity, and ultimately open up a new window to the universe through the detection and observation of gravitational waves. In this paper, a simple and cost-effective design for a drag-free nanosatellite for autonomous Earth observation and in situ atmospheric studies is explored. The nanosatellite is composed of a single thruster to compensate for drag and an attitude control system to orient the satellite in the direction of the external disturbance. The stability of the spacecraft and its ability to recover the external disturbance force vector are demonstrated on a flight-ready nanosatellite processor interfaced with a personal computer, modeling the spacecraft dynamics.