Comparison of control moment gyroscope control laws for a spacesuit

Abstract

This report investigates and compares steering laws for a control moment gyroscope (CMG) attitude control system for a spacesuit. If there is an inadequate level of control in a CMG system then the angular momentum vectors of individual CMGs may become aligned. This state, referred to as a ‘singularity state’, prevents the system from being able to produce torque in one or more directions. The steering law problem has been defined and the momentum envelope is presented to visualize system singularities. A literature review has been conducted to find applicable steering laws that may be used to control a spacesuit sized system and avoid singularities in the momentum envelope. Six potential steering laws are identified as being potentially applicable to a spacesuit sized system; the Moore-Penrose pseudoinverse (MPI), offline planning, preferred gimbal angle, linearly constrained, null motion, and the singularity-robust inverse (SRI). A conceptual pyramid configuration system of 4 CMGs has been constructed to analyse the selected steering laws through a qualitative and quantitative comparison. The qualitative assessment investigates several criteria; the singularity handling method, induced torque error, system efficiency and full utilization of hardware, convergence to singularity arrangements, and the potential for generalization to other CMG arrangements. The results of the qualitative comparison conclude that the SRI control law is the most viable for use with a spacesuit. A computational model was used to compare the behaviour of the conceptual system using the MPI and the SRI control laws. The simulation results support the qualitative analysis. The SRI control law successfully navigates around singularities by inducing a small, proportional torqueing error. It is concluded that a CMG control system can potentially be used with a spacesuit and that the SRI control law is the most viable method to avoid singularities during operation.