Balancing of a Small Satellite Attitude Control Simlator on an Air Bearing

This paper discusses the balancing of a groundbased satellite simulator. The simulator uses an air bearing as the primary method for the emulation of the frictionless environment of space. Of particular concern for accurate simulation is system balancing. 'Balancing' refers to the process of moving the center ofmass(CM) of the simulator near to the center of rotation(CR) of the air-bearing to reduce the interference of gravitational torques. This paper develops an automatic balancing system for the simulator. This system calculates the system center of mass by analyzing the dynamic sensor data along with the integrated equations of motion. The algorithm uses the method of least squares to estimate the vector from the center of rotation to the center of mass. The center of mass of the simulator is then moved near to the center of rotation by means of movable masses that are adjusted to the correct location. The algorithm is able move the center of mass to a location closer than two hundredths of a millimeter from the center of rotation. This adjustment increases the period of oscillation of the simulator to more than 60 seconds. Nomenclature I Mass moment of inertia tensor w Angular velocity vector r Vector: CR to CM MTHR Applied moment vector from thrusters B Aerodynamic drag coefficient 8 Euler angle vector <P X Euler angle 6 Y Euler angle lf1 Z Euler angle m System mass g Gravitational acceleration t time