ESTCube-1 attitude determination
Date
2015-10-27
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Abstract
Uuring viidi läbi Tartu Ülikoolis, Tartu Observatooriumis, Soome Meteoroloogia instituudis ja Eesti tudengisatelliidi programmis. Doktoritöös tutvustatakse satelliidi ESTCube-1 asendi määramise süsteemi, mille otstarve on satelliidi orientatsiooni kindlakstegemine erinevate taustsüsteemide suhtes. ESTCube-1 on ehitatud vastavalt CubeSat standardi nõuetele (≈ 10 cm × 10 cm × 10 cm) ja saadeti orbiidile 2013. aasta mais, kus see tegutses kuni 2015. aasta maini. Selle põhimissiooniks oli katsetada Maa orbiidil elektrilise päikesepurje tehnoloogiaid. Elektriline päikesetuulepuri on uudne Päikesesüsteemis liikumise moodus, mis kasutab tõukejõu saamiseks Päikeselt väljapursatavate elektriliselt laetud osakeste voogu ehk päikesetuult.
ESTCube-1 asendi määramise süsteemi põhieesmärgiks on leida satelliidi orientatsioon parema täpsusega kui 2° järgmiste tegevuste jaoks: satelliidi suure kiirusega pöörlema panemisel (sajad kraadid sekundis) tsentrifugaaljõu abil purje väljakerimiseks ja selle protsessi jälgimiseks, päikesepurje elektrilisel laadimisel sünkroonis satelliidi pöörlemisega ning mõõtmaks nurkkiiruse muutumist laetud päikesepurje ja ionosfääri plasma vahelise elektrostaatiline jõu tulemusel.
Asendi määramise süsteem koosneb magnetomeetridest, nurkkiiruseanduritest ja Päikese suuna anduritest. Maa magnetvälja ja Päikese asukoha mudeleid kasutati vastavate andurite mõõtmistega võrdlemiseks. Asendi määramiseks kasutati Kalmani filtrit. Süsteem karakteriseeriti laboratooriumis ja simulatsioonidega enne starti. Orbiidil parendati süsteemi oluliselt tarkvara uuenduste ja uuesti karakteriseerimisega. Sõltumatuks valideerimiseks kasutati satellidi poolt tehtud fotodel põhinevat orientatsiooni leidmise meetodit. Süsteemi karakteriseerimise ja valideerimisega näidati, et asendi määramise täpsus on parem kui 1,75° mis täidab eksperimendi poolt seatud nõudeid.
This research was carried out at the University of Tartu, Tartu Observatory, the Finnish Meteorological Institute and the Estonian Student Satellite Programme. This thesis presents the ESTCube-1 attitude determination system. The attitude is the satellite's orientation is space. ESTCube-1 is a satellite built according to the one-unit CubeSat standard (≈ 10 cm × 10 cm × 10 cm). The satellite was launched in May 2013 and operated until May 2015. The main scientific mission of ESTCube-1 was to perform the first in-orbit electric solar wind sail demonstration. The electric solar wind sail is a propellantless propulsion technology concept. The sail consists of long, thin, centrifugally stretched and positively charged tethers that deflect charged particles in the solar wind, hence generate spacecraft thrust. The main requirement of the ESTCube-1 attitude determination system is to determine the attitude with an accuracy better than 2° for the following purposes: high rate spin control (hundreds of degrees per second) for centrifugal tether deployment; monitoring of tether deployment; to trigger the charging of the tether in synchronisation with the satellite spin; to measure angular velocity changes caused by the Coulomb drag interaction between the charged tether and the surrounding ionospheric plasma. The attitude determination system has Sun sensors, magnetometers and gyroscopic sensors. A geomagnetic field model and a Sun position model were used to reference the respective sensor measurements. A Kalman filter was used to estimate the attitude. Before the launch, the system was characterised in the laboratory and by simulations. With in-orbit recalibration and validation, the system was significantly improved. For validation, an independent attitude determined from on-board images was used. By characterising and validating the system, it was shown that attitude determination accuracy is better than 1.75°, hence fulfils the requirement set by the electric solar wind sail experiment.
This research was carried out at the University of Tartu, Tartu Observatory, the Finnish Meteorological Institute and the Estonian Student Satellite Programme. This thesis presents the ESTCube-1 attitude determination system. The attitude is the satellite's orientation is space. ESTCube-1 is a satellite built according to the one-unit CubeSat standard (≈ 10 cm × 10 cm × 10 cm). The satellite was launched in May 2013 and operated until May 2015. The main scientific mission of ESTCube-1 was to perform the first in-orbit electric solar wind sail demonstration. The electric solar wind sail is a propellantless propulsion technology concept. The sail consists of long, thin, centrifugally stretched and positively charged tethers that deflect charged particles in the solar wind, hence generate spacecraft thrust. The main requirement of the ESTCube-1 attitude determination system is to determine the attitude with an accuracy better than 2° for the following purposes: high rate spin control (hundreds of degrees per second) for centrifugal tether deployment; monitoring of tether deployment; to trigger the charging of the tether in synchronisation with the satellite spin; to measure angular velocity changes caused by the Coulomb drag interaction between the charged tether and the surrounding ionospheric plasma. The attitude determination system has Sun sensors, magnetometers and gyroscopic sensors. A geomagnetic field model and a Sun position model were used to reference the respective sensor measurements. A Kalman filter was used to estimate the attitude. Before the launch, the system was characterised in the laboratory and by simulations. With in-orbit recalibration and validation, the system was significantly improved. For validation, an independent attitude determined from on-board images was used. By characterising and validating the system, it was shown that attitude determination accuracy is better than 1.75°, hence fulfils the requirement set by the electric solar wind sail experiment.
Description
Väitekirja elektrooniline versioon ei sisalda publikatsioone.
Keywords
ESTCube-1, satelliidid (tehn.), asendimääramise süsteem, kosmosetehnoloogia, ESTCube-1, satellites, space technology