Browsing by Author "Wessels, Jurie Hendrik"

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    Infrared horizon sensor for CubeSat implementation
    (Stellenbosch : Stellenbosch University, 2018-03) Wessels, Jurie Hendrik; Steyn, H. W.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
    ENGLISH ABSTRACT: Attitude determination is essential in satellite design, as it directly affects the pointing ability of the satellite. In the CubeSat industry there exists a need for high accuracy attitude sensors that are lowpower and low-cost. Currently, horizon sensors are a desirable option, but with recent growth in thermopile technology, it is possible to create horizon sensors that operate in the infrared spectrum offering tremendous benefits. This study focusses on the design, development, and evaluation of such an infrared horizon sensor. This includes the circuit and PCB design, software development and embedded implementation, as well as the creation of simulation/emulation environments for sensor calibration and evaluation. The critical limitation of this study is the extremely low resolution of the infrared camera (32 x 31 pixels) from which the horizon location should be determined to a sub-pixel accuracy. This limitation is overcome by calculating the gradient image with use of a Sobel Operator, after which the sub-pixel local extrema is determined by approximating a parabola shape on the horizon edge. In conclusion, a robust, low-power and low-cost sensor were developed, that is implementable on a Cube- Sat. This sensor delivers a worst case elevation accuracy of 0.075° with added noise of σ = 0:023°. Similarly, the rotation measurement delivers a worst case accuracy of 0.39° with added noise of σ = 0:14°. This satisfies the initial goal of reaching 0.1° elevation measurement accuracy.