Shape change actuation for precision attitude comtrol - Control Systems Magazine, IEEE

T he dynamics and control of spacecraft have been widely studied because of their technological significance [1]–[3]. For single-axis rotation, a rigid spacecraft can sometimes be viewed as a double integrator with torque input [4]. Three-dimensional rotation is more complex and involves three-axis torque inputs provided by thrusters with attitude and rate sensing. The problem becomes more difficult if fewer than three thrusters are available [5]–[7]. It is usually assumed that the mass distribution, and, thus, the inertia matrix, of the spacecraft is known, although robust and adaptive methods can be used when the inertia is uncertain [8]. Alternatively, control torques can be provided by reaction and momentum wheels, in which case the spacecraft mass distribution is constant despite the presence of moving components [9]. Many spacecraft use control moment gyros, which involve momentum wheels spinning at a constant rate and whose axis of rotation can be controlled through a singleor double-gimbal mechanism [10]. Although both thrusters and wheels can be used to apply control torques to the spacecraft, they play very dif© M A S T E R S E R IE S & E Y E W IR E An air spindle testbed for experimental investigation.