“In-orbit ADCS Results and Achievements on SSTL Nano to Minisatellites”


 Over the last couple of years SSTL has gain several new experiences regarding satellite attitude control systems.  These achievements will be summarised, starting from the minisatellite UoSAT-12, the first 3-axis controllable SSTL satellite launched in April 1999.  The initial attitude acquisition results from random tumbling after launcher seperation until nadir capture, using mostly magnetic attitude control, is discussed.  A combination of reaction/momentum wheel and cold gas thruster control procedures is used to stabilise UoSAT-12 in a nominal nadir pointing attitude, track targets for imaging on the earth surface, point the cameras towards the moon or the solar panels for maximum power tracking towards the sun.  In-orbit calibration of the attitude sensors (e.g. magnetometer, sun and horizon sensors), the coldgas thrusters and satellite moment and product of inertia parameters, will be presented.   Tsinghua-1 launched in June 2000 was the first SSTL microsatellite with full 3-axis control capability.  With 3 small reaction wheels, magnetorquer coils and only magnetometers plus sun sensors as attitude sensors, it achieved good nadir and off-pointing attitude results.  This ability greatly enhanced the imaging opportunities on future microsatelites.  SNAP-1, launched at the same time as Tsinghua-1, is SSTL's first nanosatellite.  It was also the first nanosatellite successfully commissioned with an active control system and 3-axis stabilisation capability.  The initial atttiude acquisition results, cancellation of a disturbance magnetic moment and the final nadir pointing performance, using only a miniature Y-momentum wheel and torque-rods, will be discussed.