UNISAT-3 Attitude Determination using Solar Panel and Magnetometer Data
- Paper number
IAC-05-C1.2.06
- Author
Prof. Fabio Santoni, University of Rome "La Sapienza", Italy
- Coauthor
Dr. Fabrizio Piergentili, University of Bologna, Italy
- Year
2005
- Abstract
UNISAT-3 is the third low-cost 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 UNISAT-3 aim is testing in orbit some technological components, namely terrestrial technology solar panels, MPPT system, commercial off the shelf (COTS) magnetometer and the on-board data handling system, based on a COTS embedded system for terrestrial robotics application. The attitude control system design and manufacturing follows the UNISAT program philosophy of fast development (about one and half year from concept to launch) and low cost. The attitude stabilization system better responding to the overall program requirements is a passive magnetic attitude stabilization system, based on a permanent magnet and a energy dissipation system, which, for UNISAT-3, consists of 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. Attitude measurements are affected by many error sources. The magnetometer readings are perturbed by the permanent magnet magnetic field, which is a constant bias, and by the hysteresis rods magnetic field. This last effect is very difficult to predict, since the rods magnetization keeps memory of all the past attitudes and an exact mathematical model of the internal rods magnetization is very complicated. On the other hand, solar panel electrical data readings depend on solar panel temperature, electrical loads switching, Earth albedo. The paper describes the attitude determination of UNISAT-3 from telemetry data, including solar panels current and voltage and TAM. A number of practical considerations and mathematical methods to take into account of all the perturbing effects cited above are discussed in the paper, in order to estimate attitude from rough data. Comparison among the methods, including q-method and the Extended Kalman filter, is performed and deeply discussed. The achieved attitude estimation accuracy of the proposed methods has been evaluated using a numerical simulation, showing that, taking into account all the perturbing effects on the sensors, is on the order of 10 degrees.
- Abstract document
- Manuscript document
IAC-05-C1.2.06.pdf (🔒 authorized access only).
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