Fast star tracker hardware implementation and algorithm optimisations on a system-on-a-chip device

Von Wielligh, Christiaan Lodewyk (2019-12)

Thesis (MEng)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: Star trackers are instruments used onboard a spacecraft that utilize digital image sensors, optics and digital hardware to determine the inertial attitude of the spacecraft. Currently, these star trackers are the most accurate sensor system used onboard a spacecraft ADCS (attitude determination and control system). The majority of space missions requires high precision attitude determination which stresses the need for star trackers. Modern ADCS's, especially when making use of Control Moment Gyros (CMG's), demand fast update rates for increased agility. Star detection, a process where centroid locations are extracted from a star image, takes significant time in the star tracker pipeline. This is due to a large number of pixels that needs to be processed, causing a high computational burden on conventional microprocessors. We propose a solution where centroid extraction is implemented through novel design on an FPGA. This architecture makes it possible to extract centroid locations at the same time as the image data is streamed from the sensor. Such parallelization significantly increases the update rate of the star tracker without compromising accuracy or power usage. The final design is implemented on a Xilinx Zynq SoC (System-on-a-Chip) device, which includes an FPGA and ARM processor. Tests are performed using simulated night sky images, real star images and a live sensor. Optimized matching algorithms are implemented on the processing system and validated independently. Distortion correction and QUEST is implemented, and a fully autonomous, end-to-end star tracker, with 10 Hz update rate is demonstrated under the night sky.

AFRIKAANSE OPSOMMING: 'n Sterkamera is 'n apparaat wat die oriëntasie van 'n satelliet bepaal deur gebruik te maak van 'n kamera sensor, optika en digitale hardeware. Hierdie sterkameras is tans die akuraatste sensors beskikbaar. Meeste satelliet missies vereis baie akkurate orentiasie bepaling wat die gebruik van sterkameras noodsaaklik maak. Moderne oriëntasie beheerstelsels, veral as daar van Beheer Moment Gyros gebruik maak, vereis 'n vinnige opdateringstempo. Ster deteksie, die proses waar ster sentroïedes se posisies vanaf 'n foto bepaal word, neem baie tyd as gevolg van 'n groot hoeveelheid spikkels wat geproseseer moet word. In hierdie navorsingsprojek stel ons 'n oplossing voor waar die deteksie deur vernuwende ontwerp in 'n FPGA geimplementeer word. Hierdie argitektuur maak dit moontlik 'n ster sentroïedes te onttrek op die selfde tyd as wat die beeld-data van die sensor oorgedra word. Deur die proses in parallel te doen, is daar 'n merkbare verbetering in die opdateringtempo van die sterkamer. Die finale ontwerp is op 'n Xilinx Zynq SoC geïmplementeer. Toetse is gedoen met gesimuleerde fotos, regte ster fotos en 'n regte sensor. Die ster-identifiseering algoritme is verder geoptimeer en op 'n mikroverwerker geïmplementeer. Nadat distorsiekorreksie en QUEST toegepas is, word 'n outonome sterkamera met 'n opdateringspoed van 10 Hz gedemonstreer as 'n finale toets.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/107140
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