Integrated attitude determination system using a combination of magnetometer and horizon sensor data

Maass, E. (Eanette)
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Stellenbosch : Stellenbosch University
ENGLISH ABSTRACT: A different approach of employing attitude sensors with incomplete measurements in an attitude determination system is investigated. The amount of available attitude sensors on small satellites are limited, and the failure of sensors can be fatal when accurate attitude determination is necessary. The problem with sensors with incomplete measurements is that they must be used in combination with other sensors to obtain three dimensional attitude information. The aim is to enhance the possible number of sensor combinations that can be employed, in an attempt to improve the ability of the attitude determination system to tolerate sensor failures. An alternative sensor structure consisting of a magnetometer and two horizon sensors is presented. A method to obtain vector observations of the attitude from a combination between magnetometer and horizon sensor measurements is derived and tested. A full state Extended Kalman Filter is used to determine the satellite's attitude, attitude rate and disturbance torque from these vector observations. A second Extended Kalman Filter structure, using only magnetometer measurements, is implemented. The magnetometer Extended Kalman Filter and the horizon/magnetometer Extended Kalman Filter are integrated to obtain a single Extended Kalman Filter structure to determine the satellite's full attitude state. Integration is done by switching between the different pairs of vector information. A systematic analysis of the integrated filter's dynamic behaviour during the switching stages is done by means of a series of case studies.
AFRIKAANSE OPSOMMING: Die gebruik van oriëntasiesensore met onvolledige metingsdata in oriëntasiebepalingsstelsels is ondersoek. Slegs 'n beperkte aantal oriëntasiesensore is beskikbaar op mikro satelliete. 'n Foutiewe sensor kan dus noodlottig wees wanneer akkurate oriëntasiebepaling nodig is. Die probleem met sensore met onvolledige metingsdata is dat dit in sensor kombinasies gebruik moet word om drie dimensionele oriëntasieinligting te verkry. Die doel is dus om die moontlike aantal sensor kombinasies sodanig te vermeerder dat die oriëntasiebepalingsstelsel beter bestand sal wees teen moontlike sensor falings. 'n Alternatiewe sensor struktuur, bestaande uit 'n magnetometer en twee horison sensore, is ondersoek. 'n Metode vir die verkryging van 3-as oriëntasie inligting vanaf 'n kombinasie van magnetometer en horison sensor metingsdata is afgelei en getoets. 'n Vol toestand uitgebreide Kalmanfilter is gebruik om the satelliet se oriëntasie, oriëntasie snelheid en versteurings draairnoment vanaf die vektor observasies af te lei. 'n Tweede uitgebreide Kalmanfilter struktuur, wat slegs magnetometer metingsdata gebruik, is geïmplementeer. Die magnetometer filter en die horison/magnetometer filter is geïntegreer sodat een uitgebreide Kalmanfilter struktuur volle oriëntasie inligting kan aflei vanaf verskillende pare vektors met oriëntasie inligting. Integrasie is gedoen deur te skakel tussen die verskillende vektorpare. 'n Sistematiese analise van die geïntegreerde filter se dinamiese gedrag gedurende die oorskakelingstye is gedoen deur middel van 'n reeks gevallestudies.
Thesis (MScEng)--Stellenbosch University, 2003.
Artificial satellites -- Attitude control systems, Detectors, Magnetometer, Infrared horizon sensors, Dissertations -- Electronic engineering