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

Abstract:

 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.