THE DEVELOPMENT OF CARBON-CARBON VACUUM ENVELOPES FOR HYPERSONIC VEHICLE HEAT PIPE APPLICATIONS

HYPERSONIC VEHICLE APPLICATIONS REQUIRE COOLING ON THE WING LEADING EDGES AND COWL LEADING EDGES. HEAT PIPES CAN COOL THESE SURFACES EITHER ACTIVELY OR PASSIVELY. COOLING THE LEADING EDGE ACTIVELY REQUIRES AN AUXILIARY HYDROGEN COOLED HEAT EXCHANGER COUPLED TO THE HEAT PIPE CONDENSER. THIS METHOD ADD WEIGHT AND COMPLEXITY TO THE DESIGN. PASSIVELY COOLING THE LEADING EDGE REQUIRES A MATERIAL WITH A HIGH SERVICE TEMPERATURE BECAUSE, AT STEADY STATE, THE HEAT INPUT MUST EQUAL THE RADIATED HEAT LOAD. CARBON-CARBON IS SUCH A MATERIAL. ALTHOUGH CARBON-CARBON HAS EXCELLENT MECHANICAL PROPERTIES AT HIGH TEMPERATURE SUCH AS HIGH SERVICE TEMPERATURE, HIGH STRENGTH AND MODULUS OF ELASTICITY AND LOW DENSITY, IT DOES HAVE SHORTCOMINGS WITH RESPECT TO HEAT PIPES. CARBON-CARBON IS POROUS AND HAS A VERY LOW COEFFICIENT OF THERMAL EXPANSION. THIS PHASE I PROGRAM OUTLINES A WORK EFFORT TO EVALUATE POSSIBLESEALING TECHNIQUES/MATERIALS TO THE CARBON-CARBON SUBSTRATE. THESE SEALING MATERIALS AND METHODS WILL BE APPLIED TO TEST COUPONS AND TESTED ACCORDING TO THE ENVIRONMENTAL CONDITIONS FOR HYPERSONIC VEHICLES. THE END RESULT OF THE WORK EFFORT WILL BE A VACUUM TIGHT CARBON-CARBON HEAT PIPE ENVELOPE TO BE USED FOR WING LEADING EDGES.