LRL has the responsibility of demonstrating the feasibility of a reactor for use as a power plant for a low-altitude, high-Mach-number missile. This reactor is literally a very high power air heater which must work at temperatures in excess of 2000' F. The reactor is exposed to high loads so one of the primary problems is providing high temperature structure. Considerable effort has been devoted to developing ceramic structural elements. One of the materials considered for this purpose is silicon nitride. In ceramic structural elements operating over large temperature ranges, a major problem is coping with thermal stress. In this respect there is a similarity with the radome problem. The work on silicon nitride at LRL consisted of limited fabrication studies (principally for familiarization), measurement of properties of interest to the application, and funding of fabrication scale-up efforts.