The risk of uncontrolled large-membrane reflectors in near-Earth orbit

Orbital solar reflectors (OSRs) have been proposed as one possible solution for helping meet worldwide demands for clean, sustainable energy. Mirror-like, large-membrane reflectors would orbit in Sun-synchronous orbits (SSOs), delivering solar energy to terrestrial solar power farms (SPFs) at dawn/dusk, when energy demands are high, but solar irradiance is low. Within the near-Earth space environment, the issue of orbital debris continues to be of great concern, with international bodies such as the Inter-Agency Space Debris Coordination Committee (IADC) and European Space Agency (ESA) publishing space debris mitigation guidance. Due to their significant cross-sectional areas, large-membrane reflectors will experience a high risk of collision with space debris, and therefore, appropriate mitigation measures must be taken. Whilst some mitigation can be achieved by solar sailing the OSRs out of populated regions, this does not account for the scenario where control of the OSR is lost. In this case, the OSR’s accumulated collision risk is determined by its position within the space debris environment, governed by the highly coupled, natural orbit-attitude dynamics, including the effects of solar radiation pressure (SRP), atmospheric drag, gravity gradient, and J2 oblateness. This paper finds through analytical analysis of the coupled natural dynamics that the spin rate about an OSR normal must be carefully selected to ensure robust, rapid removal from regions of high space debris density when control is lost; mitigating the total collision risk. Full numerical simulations are also utilised to validate the analytical findings. Whilst the results in this paper focus on OSRs, the underlying findings and analysis of the dynamics will apply to varying degrees to other large planar, reflective space structures (e.g. solar sails, space-based solar power satellites etc) that would operate in low, near-polar Sun-synchronous Earth orbit.