We need optimized astrometry for future navigation techniques with nanosatellites. It can be to triangulate a threatening satellite in distress, to track an asteroid arriving from the Sun side or to measure Jovian and Saturnian moons, maybe Phobos, Deimos or bright asteroids. We are developing an on-board algorithm to dramatically enhance the accuracy of optical measurements with CubeSat hardware (imager, attitude control and CPU). It shall reach the intrinsic limit of the optical sensor itself, getting rid of platform misalignment due to the attitude determination system, taking full advantage of the best centerfinding techniques on faint or extended objects. The technique is based on the measurement of angular distances from a body to multiple known stars in the same wide field of view and the reverse gnomonic projection to the sky. We expect to reduce the extra errors (ADCS, centerfinding) by a factor of 10 to 50, and reach the tenth of a pixel or better, up to the sub-arcsec accuracy, which would be characterized as a result of the experiment. Indeed, OPS-SAT will allow a statistical demonstration in various conditions of geometry, aberrations and straylight. In addition, OPS-SAT will also benefit from statistical performances for the stability and the accuracy of the ADCS in inertial pointing, based on measurements in absolute directions. The results will also serve our current works in CubeSat autonomous navigation as a flight-proven method.
