ATTITUDE-CONTROL OF AN ORBITING TETHERED GYROSTAT

Certain classes of space-borne experiments can only be performed in a disturbance free environment. The unique dynamic characteristics of tethered satellites make these constellations ideal candidates to serve as isolation platforms. An effective method of implementing three-axis attitude control for tethered satellites is to simultaneously move the attachment point of the tether with respect to the satellite mass center (for pitch and roll) and to torque against a reaction wheel (for yaw). Nonlinear dynamical equations are derived for the model of an elastic tether connecting an orbiting parent spacecraft and a gyrostat payload. Simple proportional-derivative (PD) feedback control laws are developed and the performance of the controller is verified with numerical simulation. Results show that the derived three-axis controller is extremely effective in achieving desired payload performance.