Spacecraft thruster systems are provided that can realize station changing,
station keeping and momentum dumping in spacecraft while minimizing loss
of spacecraft service time. The systems are formed with pairs of E and W
thrusters, NE and SE thrusters and NW and SW thrusters whose thrust
directions are each defined by respective polar angles .phi. and slew
angles .alpha.. The E and W thrusters are especially suited for rapid
station changing while the remaining thrusters generate normal, tangential
and radial thrust components required for station keeping. Because all
thrusters are directed through the spacecraft's center of mass during
station changing and station keeping firings, the spacecraft's attitude is
not disturbed and loss of service time is avoided. The thrusters are
preferably gimbaled so that they can track spatial changes of the
spacecraft's center of mass or, for momentum dumping, be offset from that
center of mass. The normal tangential and radial thrust components of the
thruster systems are arranged so that station changing, station keeping
and momentum dumping are still realized after the failure of any thruster
pair.