Attitude determination and control system simulation and analysis for low-cost micro-satellites

The Air Force Academy´s latest satellite endeavor, FalconSAT-3, is a 50 kg microsatellite being developed by faculty and cadets, and is the Air Force Academy´s first attempt at achieving three axis attitude determination and control (ADCS). FalconSAT-3 will carry three payloads to conduct DoD research. The attitude requirements for FalconSAT-3 include pointing the satellite within +/- five degrees of ram direction, as well as attitude knowledge to within one degree. This paper explains the development and testing of a Simulink and Matlab based simulation that demonstrates the ability of FalconSAT-3 ADCS hardware to meet design requirements. The satellite includes a magnetometer and sun sensors, and actuators include magnetorquers, a reaction wheel, and passive attitude control from a gravity gradient boom. Implementation of attitude conventions, satellite dynamic equations, and FalconSAT-3 design characteristics are presented. Attitude estimation using linear and extended Kalman filters is explained and included in the simulation. Control laws during delibration and operational attitude maintenance for magnetorquers and a reaction wheel are also discussed. A model of probable disturbance torques in the FalconSAT-3 orbital environment, including magnetic moment, atmospheric drag, and solar pressure is also incorporated in the simulation. Attitude control of FalconSAT-3 is shown from tip-off to a Y-Thomson spin attitude. A boom deployment sequence is then simulated, and delibration of the satellite is shown using magnetorquers and a reaction wheel. Finally, operational phase attitude maintenance is shown, with FalconSAT-3 meeting all operational attitude design requirements.