Spacecraft thruster operation for improved orbital maneuver accuracy

A spacecraft, comprising:

• a body defining a center of mass:
• attitude sensing means coupled to said body, for generating attitude error signals representative of deviation of said body from a particular attitude;
• a plurality of thrusters mounted on said body, with mutually parallel thrust components in a particular direction, said thrusters being arranged in pairs, with the thrusters in each pair producing substantially opposed torques about said center of mass;
• velocity change control means coupled to said plurality of thrusters, for generating signals commanding firing of the thrusters of at least one of said pairs of thrusters, said firing being performed in pulses having a nominal on-durations during each firing cycle, for a particular total firing time duration, for thereby effecting a desired velocity change (.DELTA.V) in said particular direction;
• and
• thruster control means coupled to said attitude control means and to said pair of thrusters, for causing said on-pulse durations of said thrusters of said pair to be controlled in a differential manner, with a first thruster of said pair being fired for a duration greater than nominal by a selected amount during each said firing cycle, and a second thruster of said pair being fired for a duration less than nominal by said selected amount during the corresponding firing cycle, said selected amount of differential control during each firing cycle being in response to said attitude error signals, to vary said torque about said center of mass, while maintaining constant .DELTA.V.