A SIMULATOR OF SATELLITE ATTITUDE DYNAMICS † Pedro Tavares, Bruno Sousa, ‡ Pedro Lima Instituto de Sistemas e Robótica, pólo do Instituto Superior Técnico Torre Norte, Av. Rovisco Pais, 1 - 1096 Lisboa Codex Fax: (+351 1) 8418291 E-mail: † pts@isr.ist.utl.pt, ‡ pal@isr.ist.utl.pt Abstract: This article describes a simulator of small satellite attitude environment and dynamics, complete with a set of realistic sensors and the most commonly used actuator in this class of satellites. The simulator described is useful in attitude estimation and control algorithm development. Some results of the simulation of the PoSAT-1 satellite are presented. Keywords: simulators, satellite control, attitude, dynamics, sensors, magnetic field computation. LIST OF SYMBOLS The following symbols were used in this article 1 : I moment of inertia matrix angular momentum vector of the SCS relative to the ICS expressed in the SCS ) (t SI S Ω control torque expressed in the SCS ) (t N ctrl S gravity gradient torque expressed in the SCS ) (t N gg S magnetic moment ) (t m S number of turns of the coil coil n coil current ) (t i coil area of the coil coil A µ Earth's gravitational constant distance from the satellite's centre of mass to the Earth's centre of mass. CM R attitude quartenion q fourth scalar component of the attitude quartenion 4 q 0 ω satellite's orbital angular velocity M mean anomaly eccentric anomaly E eccentricity e 1 This work was supported by PRAXIS XXI program project PRAXIS/3/3.1/CTAE/1942/95 true anomaly ν r distance to Earth's centre-of-mass (CM) semimajor axis of the orbit a mean motion n unit vector orthogonal to the coil plane coil S n orbital period orbit T argument of perigee ω Ω longitude of the ascending node inclination of the orbit i position of the satellite in the orbital plane Z Y X i i i , , r geocentric distance θ coelevation φ East longitude from Greenwich equatorial radius (6371.2 Km adopted for the International Geomagnetic Reference Field - IGRF) a ) , , ( φ θ r V potential function Schmidt normalised Legendre functions m n P m n P , Gauss normalised Legendre functions (Schmidt normalised) gaussian coefficients m n m n h g , m n m n h g , , , (Gauss normalised) gaussian coefficients Earth's geomagnetic field B components of B in the LHCS k j i B B B , ,