Interferometric imaging of geo-synchronous satellites with ground-based telescopes

Inteferometric imaging with arrays of telescopes is now a routine technique in optical/infrared astronomy, delivering images with nano-radian resolution. Sensitive next generation arrays, such as the Magdalena Ridge Observatory Interferometer, thus offer a potentially important capability for space situational awareness, allowing satellites in geo-synchronous Earth orbit (GEO) to be inspected after launch. A critical factor for such observations is a lack of short spacings between the telescopes comprising the interferometric array. Large GEO satellites are frequently 20-30m in size, hence ideally the shortest spacings used for the observations should be between 1.2-1.8m for observations at 1 μm wavelength. These cannot easily be realised with existing separated-element arrays. In this paper we explore the approach of combining observations from a separated-element interferometer with interferometric data obtained by optical masking of a “single-dish” telescope. We present simulations that demonstrate that substantial improvements in image fidelity can be achieved in this way. Two shapes of generic satellite shape are investigated, intended to be representative of the majority of bright GEO targets, and the efficacy of the method is assessed for these different target shapes and differing brightness levels.