Application of a Differential Drag Controller to a Full System Simulation

Abstract

Differential drag control presents an opportunity to control satellites without the use of a fuel-based propulsion system. The relative state of a pair or formation of satellites can be controlled via relative accelerations provided by a differential drag force. The drag acceleration of each vehicle can be altered by changing the area of the vehicle in the direction of motion. In research to date, differential drag controllers have been considered separately from state estimation systems that will be used for orbit determination. This paper examines an integrated system that combines a state estimator with a differential drag controller. A Kalman filter is used to estimate position and velocity elements with realistic levels of measurement noise, as well as measurement biases and atmospheric density. A differential drag controller based on the Hill-Clohessy-Wiltshire equations is presented that takes estimates from the Kalman filter and determines the appropriate control behavior. Modifications are made to the controller to reduce unnecessary actuations due to relative state error. The integrated system is tested with a nonlinear propagation model including the effects of J 2, dynamic modeling errors, and an altitude-varying atmosphere to determine the controller performance in a realistic mission environment.