Abstract: The system includes a reflector assembly mounted on a first one of a pair of spacecraft. The reflector assembly includes a mirror around which are positioned a mirror and retroreflectors. A light source mounted on the second spacecraft illuminates the assembly the reflections from which are directed into a radiometer which is also mounted on the second spacecraft. The mirror has a known curvature, and the known curvature in conjunction with the retroreflectors allow calculation of the position and motion parameters of the first spacecraft relative to the second.