Solar Thermal Propulsion For Microsatellite Manoeuvring.

Solar thermal propulsion (STP) is a 40-year-old concept that, despite substantial ground test heritage, still awaits its first flight experiment. It is simple in theory, relying neither on combustion nor electrical power to operate. Instead, incident sunlight, concentrated by a factor of 10,000 or more, heats a refractory metal or ceramic cavity receiver to temperatures of 2,000-3,000 K. A monopropellant—hydrogen being the most often proposed—is expelled through the receiver body and heated, then exhausted to provide thrust. Specific impulses of up to 1,000 s. are believed to be achievable. A more realistic approach for the near-term, proposed by the author, eschews hydrogen, which must be stored as a cryogenic liquid, for storable propellants such as ammonia or water, with the resultant decrease in specific impulse made up for by a concomitant decrease in system complexity. Nevertheless, propulsive performance is predicted to be on par with state-of-the-art chemical propulsion systems. The thesis will trace the development of the microsatellite solar thermal engine from conception through mission analysis, design, modelling, fabrication, component, and system testing. On-sun testing of 14-cm and 56-cm diameter solar concentrating mirrors has clearly validated initial optical ray trace modelling and suggests that there is significant performance margin built into test concentrators. Electrical heating tests on two solar cavity receivers, the Mk. I and Mk. II, have demonstrated the designs’ robustness at temperatures approaching 2,000 K, over many thermal cycles. Flow testing—in nitrogen, helium, and ammonia—demonstrated the Mk. I’s excellent heat transfer capability and the Mk. II’s survivability over multiple firing cycles. A novel solar thermal engine concept, utilising low-attenuation optical fibre for power transfer to a remote receiver, has been shown to permit the decoupling of the receiver from the concentrating mirror’s focus, permitting multiple mirror inputs to heat a single receiver and allowing the receiver to be placed anywhere on the host spacecraft, minimising design and operational impacts. A variant of this engine is intended to fly aboard a Surrey satellite by 2006