Durable high temperature materials are required for reusable hypersonic structural thermal protection systems. In particular, temperatures exceeding 2700ºF, and approaching 3000ºF, are targeted for capable structural materials that can survive stresses on the order of 10 ksi (70 MPa) for at least 100 hours in an oxidizing environment. Such materials have been identified as an enabling material for future hypersonic vehicles As this application is structural, a strong degree of damage tolerance is desired, and thus ceramic matrix composites are the primary choice due to the desire for reduced weight, high temperature strength and oxidation resistance. Silicon carbide fiber-reinforced silicon carbide matrix (SiC/SiC) composites are believed to be the most suitable solution due to meeting the requirements with the limitations of creep at the highest temperatures/loads, and oxidative attack at stresses that exceed the materials proportional limit. The proposed effort will define the temperature-stress limit of SiC/SiC composites, and examine methods to further extend this limit.