Doctoral Degrees (Electrical and Electronic Engineering)

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Browsing Doctoral Degrees (Electrical and Electronic Engineering) by browse.metadata.advisor "Barnard, Arno"

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    Fast star tracker hardware implementation and algorithm optimisations on a system-on-a-chip device
    (2019-12) Von Wielligh, Christiaan Lodewyk; Visagie, Lourens; Barnard, Arno; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
    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.