Abstract: A system for precisely determining directionality of an output beam includes a beam source and a body position identifier facing opposite directions, with a grating rhomb positioned to provide an attenuated sample beam from the beam source into the oppositely directed body positioned identifier. In the preferred embodiment, the beam source is a pulsed laser source and the body position identifier is a star tracker for forming a stellar map. The grating rhomb includes first and second grating members. The first grating member extends across the optical path of the output beam and has a geometry to diffract a minor portion of the output beam intensity while passing a major portion of the output beam for continued propagation in a first direction. The second grating member is positioned to traverse the field of view of the body position identifier.