Development of an attitude guidance and control system for the Thunderstar suborbital spacecraft

This paper outlines a method of developing a quaternion attitude guidance and control system for a rigid body suborbital spacecraft using cold gas thrusters over a short-duration mission. It has been specifically developed for integration aboard the Thunderstar spacecraft of Starchaser Industries, a three-man capsule designed for space tourism. The system described consists of three principal components: an autoflight computer that generates incidence and roll rate demands from analysis of the predicted flight path trajectory, a quaternion controller that produces a demand torque, and a pulse-width pulse-frequency modulator that determines the necessary thruster fire signals. The spacecraft attitude and flight path dynamics are defined within the upper to middle Earth atmosphere together with the cold gas thruster dynamics. The effect of disturbances on spacecraft attitude has been investigated and the most significant found to be due to crew motion and aerodynamics. The system concept has been evaluated through modelling in SIMULINK and has been found to meet the requirements laid out for a typical Thunderstar mission. © IMechE 2007.