A multi-mode attitude determination and control system for small satellites

Thesis (PhD)--Stellenbosch University, 1995.ENGLISH ABSTRACT: New advanced control techniques for attitude determination and control of small (micro) satellites are presented. The attitude sensors and actuators on small satellites are limited in accuracy and performance due to physical limitations, e.g. volume, mass and power. To enhance the application of sophisticated payloads such as high resolution imagers within these confinements, a multi-mode control approach is proposed, whereby various optimized controller functions are utilized during the orbital life of the satellite. To keep the satellite's imager and antennas earth pointing with the minimum amount of control effort, a passive gravity gradient boom, active magnetic torquers and a magnetometer are used. A "cross-product" detumbling controller and a robust Kalman filter angular rate estimator are presented for the preboom deployment phase. A fuzzy controller and magnetometer full state extended Kalman filter are presented for libration damping and Z-spin rate control during inactive imager periods. During imaging, when high performance is required, additional fine resolution earth horizon, sun and star sensors plus 3-axis reaction wheels are employed. Full state attitude, rate and disturbance estimation is obtained from a horizon/sun extended Kalman filter. A quaternion feedback reaction wheel controller is presented to point or track a reference attitude during imaging. A near-minimum time, eigenaxis rotational reaction wheel controller for large angular maneuvers. Optimal linear quadratic and minimum energy algorithms to do momentum dumping using magnetic torquers, are presented. A new recursive magnetometer calibration method is designed to enhance the magnetic in-flight measurements. Finally, a software structure is proposed for the future onboard implementation of the multi-mode attitude control system.AFRIKAANSE OPSOMMING: Nuwe gevorderde beheertegnieke vir die oriëntasiebepaling en -beheer van klein (mikro-) satelliete word behandel. Die oriëntasiesensors en -aktueerders op klein satelliete het 'n beperkte akkuraatheid en werkverrigting as gevolg van fisiese volume, massa en kragleweringbeperkings. Om gesofistikeerde loonvragte soos hoë resolusie kameras binne hierdie tekortkominge te kan hanteer, word 'n multimode beheerbenadering voorgestel. Hiermee kan 'n verskeidenheid van optimale beheerfunksies gedurende die wentelleeftyd van die satelliet gebruik word. Om die satellietkamera en -antennas aardwysend te rig met 'n minimale beheerpoging, word 'n passiewe graviteitsgradiëntstang, aktiewe magneetspoele en 'n magnetometer gebruik. 'n "Kruisproduk" onttuimellings beheerder en 'n robuuste hoektempo Kalmanfilter afskatter is ontwikkel vir die periode voordat die graviteitsgradiëntstang ontplooi word. 'n Wasige beheerder en 'n volledige toestand, uitgebreide Kalmanfilter afskatter is ontwikkel om librasiedemping en Z-rotasietempo beheer te doen gedurende tydperke wanneer die kamera onaktief is. Gedurende kamera-opnames word hoë werkverrigting verlang. Fyn resolusie aardhorison, son en stersensors met 3-as reaksiewiele kan dan gebruik word. 'n Volledige oriëntasie, hoektempo en steurdraaimoment Kalmanfilter afskatter wat inligting van bogenoemde sensors gebruik, is ontwikkel. 'n “Quaternion” reaksiewiel terugvoerbeheerder waarmee die satelliet na verwysings oriëntasiehoeke gerig kan word of waarmee oriëntasiehoektempos gevolg kan word, word behandel. 'n Naby minimumtyd, "eigen"-as reaksiewielbeheerder vir groothoek rotasies is ontwikkel. Optimale algoritmes om momentumontlading van reaksiewiele met lineêre kwadratiese en minimumenergie metodes te doen, word afgelei en aangebied. 'n Nuwe rekursiewe kalibrasietegniek waarmee 'n magnetometer outomaties gedurende vlug ingestel kan word, is ontwikkel. Ten slotte, word 'n programstruktuur voorgestel vir aanboord implementering van die nuwe multimode beheerstelsel

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