Attitude Control of Large Gossamer Spacecraft Using Surface Reflectivity Modulation

Gossamer spacecraft are ultra-lightweight structures which deploy large, thin reflective membranes. Since the on-board attitude control systems need to be high-performance, reliable and importantly lightweight, this work investigates the use of thin-film reflectivity control devices across the membrane surface for attitude control. These coating elements can modify their surface reflectivity, which modulates the solar radiation pressure acting on the surface. Consequently, the total body force and torque can be controlled 'optically' without using additional mechanical systems or thrusters. The membrane is modelled using discrete reflec- tivity cells (as in a dot matrix) across the surface. The elements can maintain two states: either high (power on) or low reflectivity (power off). The aim is towards finding the optimal reflectivity pattern in terms of number and combination of active cells to create a required control torque. The control problem is solved using a quaternion feedback scheme, under consideration that the system is under-actuated, since through the concept of surface reflectivity modulation presented here, torques can be created in the membrane plane only. The optical actuator is applied successfully to perform a basic spacecraft manoeuvre from an initial arbitrary attitude state towards Sun-pointing on a Sun-centred orbit