µm-class Control of Relative Position and Attitude for a Formation Flying Synthetic Aperture Telescope with Micro-satellites

Abstract

Earth remote sensing from geostationary orbit (GEO) can realize high temporal resolution; however, the spatial resolution is commonly worse than observation from low Earth orbit. In order to achieve high-frequency and high-resolution GEO remote sensing, a “Formation Flying Synthetic Aperture Telescope (FFSAT)”with multiple micro-satellites has been proposed. The FFSAT greatly improves the spatial resolution using a synthetic aperture technique. Therefore the relative positions and attitudes between the optical units of each satellite must be controlled with an accuracy better than 1/10 of the observation wavelength. However, even mm-class accuracy control has not been demonstrated on orbit. As a first practical application of the FFSAT, a forest fire monitoring mission using infrared rays is being considered, in which control accuracy requirement is relaxed as its wavelength is longer than visible light. We proposed a point spread function optimization method for controlling formation flying with an accuracy of approximately 1–1,000 times the wavelength (1 μm–1mm) in the absence of sensors, which can measure absolute distance with μm-accuracy. The effectiveness of the method was demonstrated through simulations in which the satellites’ system and the optical system are coupled. The simulation results show that the method can control the formation within the wavelength order.