Design of elliptic orbit constellations for solar reflectors for terrestrial solar energy enhancement
Onur Çelik (TU Delft - Aerospace Engineering)
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Abstract
Orbiting solar reflectors (OSR) are large, thin, flat and ultralightweight structures proposed to extend the operational hours of solar power farms (SPF) beyond the daylight hours by locally illuminating them at night from orbit. They operate with the principle of intercepting incoming sunlight and reflecting an image of the solar disk onto a ground target by tracking. It has been previously shown that a constellation of modest number of OSR in circular, Sun-synchronous low-Earth orbits can increase the efficiency of terrestrial SPF considerably [1]. The design of such constellations typically relies on circular orbits due to the reduced complexity of orbit selection and optimising the constellations for a given objective, where analytical expressions are available for simple constellation patterns. Introducing nonzero eccentricity to orbit shape immediately multiplies the complexity of the optimisation problem as the number of available orbits are in principle infinite, but their employment in the design would enhance the flexibility in mission design and may offer an improved performance. This paper therefore investigates the design of optimal OSR constellations with elliptic Sun-synchronous orbits with an objective to maximise the daily quantity of energy delivered. An analytical approach is used to simplify the design process by placing reflectors in different orbit planes that allow reflectors to follow the same pass geometry over a given target, reducing the constellation optimisation to effectively a single groundtrack optimisation, carried out by a genetic algorithm for full orbital element space except semi-major axis. The results demonstrate that introducing eccentricity at three different semi-major axis values increase the daily quantity of energy delivered by up to 20%, offering flexibility in constellation design with reduced complexity that can be applied applications beyond terrestrial space-based solar power.