http://www.loc.gov/mods/v3 http://www.loc.gov/standards/mods/v3/mods-3-2.xsd
Nonlinear attitude control of spacecraft and momentum management of control moment gyros
Nonlinear design procedures are presented for obtaining attitude control and momentum management laws. These are based on the Liapunov stability theorems. The Work-Energy Rate(WER) principle is extended to cover general classes of systems. It is shown that the use of the W ER principle for obtaining control laws, can reduce the design efforts. The attitude control laws are designed for several types of missions, i.e., absolute attitude and relative attitude control. The momentum management as well as attitude control laws are designed for both stable and unstable spacecraft configurations which use Control Moment Gyros(CMGs) as active actuators. A large stability region is found around the local-vertical-local-horizontal(LVLH) equilibrium point, and so the designed control laws can be used even in the event of large initial attitude deviations from LVLH. In the presence of constant disturbance, the momentum is managed by seeking a Torque Equilibrium Attitude(TEA) where the disturbance torque is balanced by gravity gradient and gyroscopic torques. This is done by the use of integral feedback of the control torque, which is related to the angular momentum of the CMGs. It is shown that the unknown constant disturbance can be identified by the use of integral feedback. Cyclic disturbance rejection for the pitch axis is performed by successive stabilization and integral feedback. Theoretical results developed are verified using both experimental and numerical simulations. Experimental model of a flexible spacecraft is used to demonstrate the applicability of the WER principle and the fact that under certain conditions, a control law based on a rigid body model, can be applied to a flexible spacecraft. Using a mathematical model of the space station Freedom, several attitude/momentum management control laws are simulated and shown to work successfully with/without a constant disturbance torque. The control law for cyclic disturbance rejection of pitch axis attitude is examined and found to work satisfactorily under the presence of cyclic disturbance.