TUFROC (Toughened Uni-piece Fibrous Reinforced Oxidation- resistant Composite) has been developed as a new thermal protection system (TPS) material for wing leading edge and nose cap applications. The composite withstands temperatures up to 1,970 K, and consists of a toughened, high-temperature surface cap and a low-thermal- conductivity base, and is applicable to both sharp and blunt leading edge vehicles. This extends the possible application of fibrous insulation to the wing leading edge and/or nose cap on a hypersonic vehicle.
The lightweight system comprises a treated carbonaceous cap composed of ROCCI (Refractory Oxidation-resistant Ceramic Carbon Insulation), which provides dimensional stability to the outer mold line, while the fibrous base material provides maximum thermal insulation for the vehicle structure. The composite has graded surface treatments applied by impregnation to both the cap and base. These treatments enable it to survive in an aero-convectively heated environment of high-speed planetary entry. The exact cap and base materials are chosen in combination with the surface treatments, taking into account the duration of exposure and expected surface temperatures for the particular application.
Current leading edge TPS systems weigh approximately 1.6 g/cm3, while the TUFROC version weighs 0.4 g/cm3. The RCC system used on the orbiter operates at heat fluxes below 70 W/cm2 during Earth re-entry. Not only are systems like this heavier than TUFROC, they are far more expensive with RCC costing approximately 100 times more than TUFROC components of equivalent size. Furthermore, RCC requires significantly longer fabrication lead times — 12 rather than the roughly a month needed for TUFROC.
TUFROC systems have been fabricated and tested in the various configurations as shown in the figure. The 5º blunt cone is 6.35 cm thick, and has a 1.27 cm corner radius. The sharp leading edge wedge has a 10º half-angle, is 10.2 cm wide, and has leading edge radii of 0.158 cm and 0.318 cm. The blunt leading edge wedge has a leading edge radius of 5.08 cm and is 20.2 cm wide. These configurations have thermocouples installed at the junction between the cap and insulator, and in the aluminum base-plate behind the insulation. Finally, to evaluate the flight performance of a TUFROC TPS on the wing leading edge of the X- 37, a pylon test article was created consisting of two tiles: a base tile (20.3×20.3 cm square) with a pylon protruding from it, and an upper portion 10.2 cm long. All test articles, except the pylon, contain a threaded aluminum-mounting ring bonded into their bases so that they can be attached to a water-cooled strut.
This work was done by David Stewart and Daniel Leiser of NASA's Ames Research Center.
This invention is owned by NASA, and a patent application has been filed. Inquiries concerning rights for the commercial use of this invention should be addressed to the Ames Technology Partnerships Division at (650) 604-2954. Refer to ARC-15201-1.