Browsing by Author "Roux, Gabriel Johannes"

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    Augmented stellar sensor for a small spacecraft
    (Stellenbosch : Stellenbosch University, 2019-04) Roux, Gabriel Johannes; Steyn, H. W.; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.
    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.