Abstract
Solar thermal propulsion (STP) is the utilisation of concentrated sunlight for heating a propellant to high temperatures. Early STP concepts were envisioned for large spacecraft and capable of high levels of propulsive performance (<1000s Isp). Currently, at the University of Surrey, STP is being adapted for use on small-spacecraft in order to utilise the high propulsive capability offered by STP and widen the range of small-spacecraft applications. Conventional STP system concepts encounter difficulties in conforming to the low mass and volume requirements of a small- spacecraft platform. An enabling technology for the miniaturisation of an STP system is seen in the advent of low attenuation high numerical aperture (NA) fibre optics. This work investigates the mission and design implications of an STP system augmented with fibre optics and develops new technologies that stem from the concept. A small parabolic dish concentrator was designed to the requirements of a high NA optical fibre and manufactured for component testing. Efficiency tests of the small concentrator demonstrated 83% efficiency and an overall system efficiency of 50% including coupling light into the fibre. A fibre optic heat exchanger was designed, manufactured and tested to investigate methods of improving heat transfer efficiency. Tests of the heat exchanger demonstrated receiver absorption efficiencies of 82%. Stringent solar pointing accuracies imposed by the small concentrator-fibre optic combination resulted in the development and testing of a novel sensor technology that employs fibre optic luminescence as feedback for a concentrator pointing control mechanism. Concentrator pointing accuracies of 3 arc-minutes were experimentally demonstrated. Accompanying this work is the development of a novel algorithm for the study of coupled radiation and conduction heat transfer within participating media, which is more accurate and stable than conventional techniques. This work successfully demonstrated the potential high efficiency and feasibility of a small- spacecraft fibre augmented STP system.