The Infrared Simulation System (IRSS) at the Army's Redstone Arsenal is used to test small air-to-air IR guided missile seekers. The IRSS optics provide a dynamic field of view containing dynamic targets and backgrounds and are designed to operate over the wave-length range from near UV to 5 µm. We have studied ways in which this system could be modified so that it can also be used for testing small air-to-ground missile seekers operating passively in the 8 to 14 µm window., The existing optical system is an Offner Concentric Mirror Annular Field Projector (l) in which the secondary mirror has been dimpled to expand the input beams and allow superposition of the fields of several relatively narrow input beams. In the thermal IR this dimpled mirror inserts copious ambient radiation into the system which must be allowed for. Further in the air-to-ground case the background closes with the target whereas in the existing simulator the background is assumed to remain distant. The limitations imposed by these factors will be discussed as will the practicability of less and more sophisticated methods of circumventing these limitations.