Augmented stellar sensor for a small spacecraft

Roux, Gabriel Johannes (2019-04)

Thesis (MEng)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: With the maturity of the CubeSat industry and advancements in commercial off-the-shelf components, CubeSat-based projects have become an attractive option for advanced outer space missions. This increase in mission complexity has given rise to the necessity of a new generation of accurate attitude determination subsystems. The purpose of this work, therefore, entailed the design and development of an augmented stellar sensor. The focus was not only on the development of a suitable high-performance, lowpower hardware platform, but also on the identification, implementation, and development of suitable software techniques as well as the simulation, integration and testing of the augmented platform. This developed sensor delivers accurate attitude and rate estimates, whilst conforming to the small satellite power and size requirements. The augmented system uses inertial rate sensor data, with error compensation performed by use of matched vector measurements obtained from a star sensor. Measurements are combined in an Extended Kalman filter, providing both high rate attitude propagation and bias drift compensation. The designed system features a robust tracking mode as well as a stellar gyro algorithm to deliver accurate, low-frequency rate estimates independent of host dynamics. To prove overall system functionality, the sensor has undergone verification during simulated conditions, testing in an in-house developed star emulation environment, as well as testing under night sky conditions. During these tests, it was exposed to conditions typically experienced by satellites throughout their mission lifetimes. These conditions range from low-rate tumbling, to fine pointing. Initial testing shows that the system offers a robust response regardless of satellite rate and orientation whilst simultaneously adhering to CubeSat standards. IMU bias compensation worked successfully, and estimated results show that the average 3σ stellar gyro rate accuracies were in the order of 0.01 °/s whilst the cross-axis 3σ orientation accuracy was close to 0.01° during low rates.

AFRIKAANSE OPSOMMING: Met die volwassewording van die CubeSat-industrie en vooruitgang van kommersieël beskikbare elektroniese komponente, het die CubeSat-platform ’n aantreklike keuse geword vir ruimtevaartsendings. Hierdie belangstelling in die CubeSat-platform het tot ’n vermeerdering van sendingskompleksiteit gelei wat die behoefte vir ’n nuwe generasie akkurate oriëntasiebeheer-substelsels geskep het. Gevolglik was die doel van hierdie werk die ontwerp en ontwikkeling van ’n uitgebreide stersensor. Die fokus was egter nie net om ’n gepaste hardewarestelsel te ontwerp nie, maar ook om geskikte sagtewaretegnieke en algoritmes te identifiseer, te ontwikkel, en toe te pas. Die ontwikkelde stelsel lewer akkurate oriëntasie- en hoeksnelheidafskattings, terwyl dit geskik vir gebruik in ’n nanosatelliet is. Hierdie uitgebreide stelsel gebruik inersiële sensormetings waarop foutkorrigering, soos afgeskat deur middel van vektorinligting vanaf ’n sterkamera, toegepas is. Die sensormetings word gekombineer in ’n uitgebreide Kalman filter, wat beide hoë-frekwensie oriëntasie-afskattings kan verskaf, sowel as om die inersiële sensor foutkorrigering te beheer. Die ontwerpte stelsel bevat verder ’n robuuste stervolgmodus om die mikroverwerker se berekeninge te verminder, sowel as ’n hoeksnelheid-afskattingsalgoritme om baie akkurate lae-frekwensie afskattings te bied. Die laasgenoemde algoritme kan onafhanklik van ’n dinamiese model funksioneer. Om die oorhoofse stelsel se werking te bevestig, is die sensor tydens gesimuleerde, geëmuleerde, en praktiese omstandighede getoets. Gedurende hierdie toetse is die stelsel blootgestel aan tipiese gebruikstoestande soos lae-snelheid tuimel en fyn oriëntasiebeheer. Aanvanklike toetse wys dat die stelsel goed werk ongeag die hoeksnelheidstoestande waaraan dit blootgestel word. Inersiële sensor hoeksnelheidsmetings kon suksesvol gekorrigeer word. Afgeskatte resultate toon daarop dat ’n stervektor se hoeksnelheid oor die kruisas akkuraat tot 0.01 °/s, op die 3σ-vlak, afgeskat kon word. Resultate aangaande oriëntasie-akkuraatheid was in die orde van 0.01°, 3σ, oor die kruisas tydens ’n lae hoeksnelheid.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/106199
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