An Attitude Control System and Commissioning Results of the SNAP-1 Nanosatellite

SNAP-1 is a low-cost nanosatellite build by Surrey Satellite Technology Ltd. (SSTL), it is amongst other objectives a technology demonstrator for 3-axis stabilisation and orbit control for a future constellation of small satellites during formation flying. The satellite uses a single miniature Ymomentum wheel, 3-axis magnetorquer rods and a single butane gas thruster to ensure a nominal nadirpointing attitude with full pitch control and in-track delta-V manoeuvrability. The magnetorquer rods do momentum maintenance and nutation damping of the Y-wheel. The primary attitude sensor used, is a miniature 3-axis fluxgate magnetometer. Precise orbital knowledge will be obtained using a small single antenna GPS receiver supported by an on-board orbit estimator. This paper describes the various attitude control modes required to support: 1) a narrow and three wide angle CMOS cameras during pointing and tracking of targets, 2) the propulsion thruster during orbit manoeuvres, 3) the initial attitude acquisition phase and 4) a safe mode backup controller. The specific attitude controllers and estimators used during these modes are explained. Simulation and in-orbit commissioning results will be presented to evaluate the performance and design objectives.