ESA GNC Conference Papers Repository

ESMO is an educational mini-satellite project of the European Space Agency, planned to be the first student mission to the Moon. More than 20 student teams across Europe from the ESA Member States and ESA Cooperating States are currently working on the project. The launch is currently scheduled for 2014. ESMO objective is to reach lunar orbit and take images of the Moon. The AOCS is up to provide Sun and Moon pointing and thrust direction control during manoeuvres. Because of the educational background of the mission, low cost is one of the main drivers. In the paper, the strategies adopted to deal with this problem will be described. The AOCS is under responsibility of two teams from Politecnico di Milano (AOCS1) and University Politechnica Bucharest (AOCS2). AOCS1 duty is the design of the subsystem, the choice of h/w units and the design of AOCS software interfaces and algorithms, excluding the attitude determination and the control law, which are AOCS2 duty. The AOCS hardware baseline features sensors: 2 Star Trackers (built by SUPAERO - Tolouse), 2 Sun Sensors and 2 Inertial Measurement Units; and actuators: 4 Attitude Control Thrusters (built by Stuttgart University) and 4 Reaction Wheels. Sun Sensors, IMUs and wheels are to be provided by AOCS1. The paper will include a description of the Extended Kalman Filter used for the attitude determination based on the dynamics and kinematics of the satellite written in terms of angular rates and quaternions. It is also described the fault detection algorithm in which Student-t and chi-square tests are applied for the residuals generated using the EKF and the measurements. Two control laws are implemented and will be presented: a PD (Proportional Derivative) control and a LQ (Linear Quadratic) optimization. The paper features simulation results, by means of software testing and validation, proving AOCS subsystem performance against the mission requirements.