Christopher J. Heiberg

Rapid Multitarget Acquisition and Pointing Control of Agile Spacecraft

This paper describes the study results of developing an attitude control system for agile spacecraft which require rapid retargeting and fast transient settling. In particular, a nonlinear feedback control logic is developed for large-angle, rapid multi-target retargeting maneuvers subject to various physical constraints, including the actuator saturation, slew rate limit, control bandwidth limit, etc. Simulation results for an agile spacecraft equipped with control moment gyros demonstrate the effectiveness and robust performance of the proposed nonlinear feedback control system.

Precision control moment gyroscope spacecraft control with disturbance

Standard feedback control systems subjected to periodic disturbances often cannot avoid sustained oscillatory responses at the disturbance frequency. Periodic disturbance rejection in a feedback control system via the insertion of an oscillator in the controller (internal model principle) is an effective method and well understood. By proper pole-zero placement, stable, steady-state performance which asymptotically approaches zero is achieved through the application of this type of filter. When the periodic disturbance is variable in frequency, the application of this type of filter is achieved by allowing the oscillator frequency to follow the disturbance. This, however, presents several problems in the actual application. This paper describes two applications of a variable periodic disturbance rejection filter in a spacecraft attitude control system and discusses the problems encountered and areas of further research.

PRECISION POINTING CONTROL OF AGILE SPACECRAFT USING SINGLE GIMBAL CONTROL MOMENT GYROSCOPES

Agile spacecraft control requires high torque on demand, with low power and emitted disturbance, to maintain the attitude control, manage the spacecraft momentum, and provide structural disturbance rejection. These demands almost exclusively call for control moment gyroscopes to produce the actuation torque. Single gimbal control moment gyroscopes have been shown to have significant advantages over double gimbal control moment gyroscopes in this role. The advantage of torque amplification translates to power, cost, weight, and performance improvements over double gimbal control moment gyroscopes. However, the use of either type in agile spacecraft gives rise to problems in their implementation; 1) disturbances manifested in the gyroscope gimbal actuators are multiplied and transmitted to the spacecraft, and 2) the presence of singularities prevents utilization of the gyroscope array to its maximum potential. Linear and nonlinear external disturbances have been shown to be easily eliminated utilizing disturbance rejection filters. In addition, non-linear disturbances caused by the control moment gyroscopes that are feed-forward in nature have been shown to be mitigated using the same approach; however, nonlinear disturbances in the feedback loop are more pervasive in nature and are often more difficult to reject. This paper explores rejection of nonlinear disturbances and includes a discussion of control moment gyroscopes array configuration based on singularity and momentum considerations.