Inverse free steering law for small satellite attitude control and power tracking with VSCMGs

Advances in Space Research. 2014. Vol. 53. No. 1. P. 97–109.

Asghar S., Malik M. S.

Recent developments in integrated power and attitude control systems (IPACSs) for small satellite, has opened a new dimension to
more complex and demanding space missions. This paper presents a new inverse free steering approach for integrated power and attitude
control systems using variable-speed single gimbal control moment gyroscope. The proposed inverse free steering law computes the
VSCMG steering commands (gimbal rates and wheel accelerations) such that error signal (difference in command and output) in feedback
loop is driven to zero. H1 norm optimization approach is employed to synthesize the static matrix elements of steering law for a
static state of VSCMG. Later these matrix elements are suitably made dynamic in order for the adaptation. In order to improve the
performance of proposed steering law while passing through a singular state of CMG cluster (no torque output), the matrix element
of steering law is suitably modified. Therefore, this steering law is capable of escaping internal singularities and using the full momentum
capacity of CMG cluster. Finally, two numerical examples for a satellite in a low earth orbit are simulated to test the proposed steering
law.

Keywords: Attitude control, Inverse free steering law, Control moment gyroscope, Optimization, Singularity avoidance