Attitude Determination and Control Subsystem Hardware in the Loop Test on Air Bearing Trolley

Abstract

The Attitude Determination and Control (ADCS) suite for ATSB future nano-satellite consists of a Magnetometer Module, a Coarse Sun Sensor Module, a CMOS Horizon Sensor Module, a Reaction Wheel Module and a Gyroscope Module to provide satellite stability and body pitch slew maneuvers. The Reaction Wheel Module houses electronics that handles both the Wheel rotor and the Gyroscope which thus are connected serially to each other. Both the CMOS Horizon Sensor Module and Reaction Wheel Module are new designs using CAN bus for telemetry and telecommand to the Onboard Computer (OBC). Since these modules have yet to be flown, a Hardware in the Loop (HIL) test was implemented to determine the functional integration via the CAN bus and real-time attitude control response on an Air Bearing Trolley (ABT). The ABT is a platform floating on a thin film of air, providing 2 Degrees of Freedom (DOF) translation and 1 DOF rotation about the axis normal to the platform, or ABT pitch. The modules are mounted on the platform where the Reaction Wheel rotation axis and the Gyroscope rate sensing axis are parallel to the platform normal. The ATSB nano-satellite shall use a non-linear PID compensator for the pitch slew maneuvers and hence a single axis non-linear PID was designed specifically for the ABT. A light source was used as a reference point for relative ABT pitch control test, whereby the CMOS Horizon Sensor Module algorithm was modified and calibrated to sense the light source, giving sensor azimuth readings. A simple Kalman Filter was later designed to estimate the sensor azimuth and ABT pitch rate and fed back to the compensator. All algorithms resides on a test PC and connected via a CAN bus to the modules. The real-time ABT pitch response with the compensator and estimator using the integrated ADCS Modules on the ABT are discussed and has shown to be satisfactory for flight implementation.