An AOCS concept for the X-ray Interferometer mission

An X-ray Interferometer (XRI) has recently been proposed as a theme for ESA's Voyage 2050 planning cycle, with the prospect to observe the X-ray sky with unprecedented angular resolution. A scientifically very interesting mission is possible on the basis of a single spacecraft with a resolving power of 100 micro arcsec (~0.5 nrad), owing to the compact 'telephoto' design proposed in 2004 by Willingale. One of the key challenges for such a mission is to acquire and maintain pointing to an absolute accuracy below that resolution. This challenge was already identified by Gendreau et al. in 2003. In this paper we re-address this issue in the light of recent technological developments.