Sun-tracking commands and reaction wheel sizing with configuration optimization

Abstract

This paper is composed of two parts. In the first part, two-axis sun-tracking commands for solar arrays articulated to Earth-pointing spacecraft are developed. In the second, the paper deals with optimization of cant angle(s) of reaction wheel pyramids for minimizing power consumption and required torque and momentum capacity of the wheels to deliver a cylindrical momentum envelope and a rectangular parallelepiped torque envelope. The two commonly used four-wheel pyramid configurations and a new one, according to which the wheels are inclined to roll and yaw axes of the spacecraft at unequal angles, are analyzed in depth. The minimum torque and momentum capacity of each wheel in the four-wheel pyramids are compared with the capacity of each wheel in six- and three-wheel pyramids. Both no-wheelfailure and one-wheel-failure cases are considered for all pyramidal configurations. The literal relationships developed in the paper are very useful for quickly determining the optimum cant angle(s) and the torque and momentum capacity of the wheels for given requirements about the spacecraft axes, and for selecting a most suitable wheel configuration from six- and three-wheel pyramids, three four-wheel pyramids of different bases, and six- and three-wheel orthogonal arrangements.