The design and simulation analysis of an attitude determination and control system for a small earth observation satellite

Janse van Vuuren, Gerhard Hermann (2015-03)

Thesis (MEng)--Stellenbosch University, 2015.

Thesis

ENGLISH ABSTRACT: The ability of satellites to actively control their attitude has changed the way we live. Navigation systems, satellite television, and weather forecasting, for example, all rely on satellites which are able to determine and control their attitude accurately. This project was aimed at designing and analysing an attitude determination and control system (ADCS) for a 20 kg Earth observation satellite by means of simulation. A realistic simulation toolset, which includes the space environment, sensor, and actuator models, was created using MATLAB and Simulink. An ADCS hardware suite was selected for the satellite based on a given set of pointing and stability requirements, as well as current trends in the small satellite industry. The hardware suite consists of among others a star tracker and three reaction wheels. A variety of estimators and controllers were investigated, after which an application specific ADCS state machine was defined. The state machine included a Safe Mode for de-tumbling, a Nominal Mode for normal operation, a Forward Motion Compensation (FMC) Imaging Mode for Earth observation, and a Target Tracking Mode for ground station tracking. Simulation results indicated that de-tumbling, coarse and fine sun tracking, FMC factor 4 imaging, and target tracking were successfully implemented. Lastly, the satellite’s pointing error and stability were determined to be less than 70 arcseconds and 7 arcseconds per second respectively, both values well within the given requirements.

AFRIKAANSE OPSOMMING: Satelliete se vermoë om hul oriëntasie aktief te beheer, het die manier waarop ons lewe, verander. Navigasiestelsels, satelliettelevisie en weervoorspelling, byvoorbeeld, maak staat op satelliete wat hul oriëntasie akkuraat kan bepaal en beheer. Die mikpunt van hierdie projek was die ontwerp en analise van ’n oriëntasiebepaling- en -beheerstelsel (ADCS) vir ’n 20 kg aardwaarnemingsatelliet deur middel van simulasie. ’n Realistiese simulasieopstelling, wat modelle van die ruimteomgewing, sensore en aktueerders insluit, was ontwikkel deur gebruik te maak van MATLAB en Simulink. ’n ADCS hardewarestel was gekies vir die satelliet op grond van ’n stel rig- en stabiliteitsvereistes, sowel as die huidige tendense in die klein-satellietbedryf. Die hardewarestel bestaan onder andere uit ’n stervolger en drie reaksiewiele. Nadat verskeie afskatters en beheerders ondersoek was, was ’n toepassingspesifieke ADCS toestandmasjien gedefinieer. Die toestandmasjien het ’n Veilige Modus vir onttuimelling, ’n Nominale Modus vir normale operasie, ’n Vorentoe-bewegingskompensering (FMC) Beeldskandeermodus vir aardwaarneming en ’n Teikenvolgmodus vir grondstasie volging ingesluit. Simulasieresultate het aangedui dat onttuimeling, growwe- en fyn sonvolging, FMC faktor 4 beeldskandering en teikenvolging suksesvol geïmplementeer was. Laastens was die satelliet se rigfout en stabiliteit bepaal as minder as 70 boogsekondes en 7 boogsekondes per sekonde onderskeidelik, albei waardes gemaklik binne die vereistes.

 
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