Re-entry vehicles generally require some combination of control surfaces (e.g., rudders, body flaps, elevons) to steer or guide the vehicles during re-entry into and through the Earth's atmosphere. Control surface seals are installed between these movable surfaces and stationary portions of the vehicle both along hinge lines and in areas where control surface edges are actuated close to the vehicle body. These seals must operate in high-temperature environments and limit hot gas ingestion and transfer of heat to underlying low-temperature structures to prevent over-temperature of these structures and possible loss of vehicle structural integrity. This paper presents results for thermal analyses and mechanical testing conducted on the baseline seal design for the X-38 rudder/fin. This seal application was chosen as a case study to evaluate a currently available control surface seal design for applications in future re-entry vehicles. A thermal analysis of the rudder/fin seal assembly based on representative heating rates predicted a peak seal temperature of 1900 °F. Seals were heated in a compressed state at this peak temperature to evaluate the effects of temperature exposure. Room temperature compression tests were performed to determine load versus linear compression, preload, contact area, stiffness, and resiliency characteristics for as-received and temperature-exposed seals. For all compression levels that were tested, unit loads and contact pressures for the seals were below the 5 lb/in. and 10 psi limits required to limit the loads on the Shuttle tiles that form the adjacent sealing surface for these seals. The seals survived an ambient temperature 1000 cycle scrub test over sanded Shuttle tile surfaces and were able to disengage and re-engage the edges of the rub surface tiles during scrubbing. Arc jet tests were performed to experimentally determine anticipated seal temperatures for representative flow boundary conditions (pressures and temperatures) under simulated vehicle re-entry conditions. Installation of a single seal in the gap of the test fixture caused a large temperature drop (ΔT = 1710 °F) across the seal location confirming the need for seals in the rudder/fin gap location. The seal acted as an effective thermal barrier limiting heat convection through the seal gap and minimizing temperature increases lowdownstream of the seal to acceptable (< 200 °F) levels.