UNISAT-3 ATTITUDE DETERMINATION USING SOLAR PANEL AND MAGNETOMETER DATA

UNISAT-3 is the third educational microsatellite, completely designed built and operated in orbit by students and professors of the research group GAUSS (Gruppo di Astrodinamica dell’Università degli Studi “la Sapienza”) at Scuola di Ingegneria Aerospaziale of University of Rome “La Sapienza”. It has been launched from Baikonour Cosmodrome on 29 June 2005 using the DNEPR launcher and it is currently operating in orbit. The spacecraft is stabilized using a passive magnetic attitude stabilization system, based on a permanent magnet and a energy dissipation system, which consists on three magnetic hysteresis rods. The satellite is not equipped with dedicated attitude sensors, except for a COTS three axes magnetoresistive magnetometer (TAM). The attitude determination is performed using the magnetometer readings and the solar panels telemetry data which are affected by a number of error sources. An attitude determination strategy is proposed to deal with these perturbing effects, based on a number of practical considerations and mathematical methods, ,which do not require the a priori knowledge of the solar panel performance in orbit. Moreover this method allowed to recover a main failure occurred on the UNISAT-3 TAM. The achieved attitude estimation accuracy of the proposed methods has been evaluated on the order of 10 degrees, which fulfils the requirements of the didactical microsatellite UNISAT-3.