The UFFO pathfinder mission will attempt to locate the optical afterglow of a GRB within
seconds of its detection and location by a wide field X-ray imager. It will be mounted on
the Lomonosov spacecraft for launch in 2013 and consists of a coded mask X-ray imager UBAT
to detect a GRB and estimate a direction vector which will be passed to the SMT optical
system which will rotate a moveable mirror to lock onto the GRB and direct the optical
afterglow to a camera with a ~17′ wide aperture. We present the design geometry of
the UBAT instrument only, with results of simulations for a range of GRB types to show
probable photon integration times to be expected to extract a significant FOV image
reconstruction and GRB location.