Full attitude determination specification - small libration version - of the Alsat-1 first Algerian microsatellite in orbit

Abstract

The goal of attitude determination is to determine the orientation of the spacecraft relative to either an inertial reference frame or a frame referenced to some specific object of interest, such as the Earth. To do this we need the following: (1) First of all we must have available one or more reference vectors, i.e. unit vectors in known directions relative to the spacecraft (commonly used reference vectors are the Earth's magnetic field, and the unit vectors in the direction of the Sun, a known Star, or the centre of the Earth). (2) Given a reference vector, an attitude sensor measures the orientation of that vector (or some function of the vector) in the frame of reference of the spacecraft body. (3) Having done this for two or more vectors, we may compute the orientation of the spacecraft relative to these vectors. This paper describes the full attitude determination specification -Extended Kalman filter- using magnetometer and sun sensor measurement of the Alsat-1 first Algerian microsatellite in orbit : (1) Theoretical preliminaries on extended Kalman filter algorithm, (2) Extended Kalman filter application to Alsat-1 (System model, Process and Observation noise matrix), (3) In orbit results will be presented to evaluate the performance of the filter, (4) Conclusion.