Detection of Debonding in Thermal Protection Tile System
Using Pulsed Laser Sources
Sponsor: Florida Space Grant Consortium
The thermal protection system (TPS) of the Space Shuttle Orbiter is unique when compared to other atmospheric reentry vehicles in that, along with other Orbiter subsystems, it is reusable. The shuttle TPS is more than just tiles and blankets—it is the integration of the materials, development, design concepts, fabrication techniques, installation processes and refurbishments procedures used to protect a vehicle from the severe heating environment of atmospheric reentry. Each orbital vehicle possesses about 24,300 Reusable Surface Insulation (RSI) tiles, some of which loose bond integrity during repeated flights. Thus, it is required to test many suspect tiles after each flight. The most common technique that is used by NASA to check the bonding of the tiles is via a pull test. A suction device is attached to the tile to be tested, and a test load of 10 psi is applied to the tiles. If the tile withstands the prescribed load, the bond is considered safe. If the tile is torn from the space shuttle skin, the bond quality is not nominal and the tile needs to be reinstalled. But this technique is not efficient as it poses harm to the tile assembly itself. Application of the test load may damage the bond between the space shuttle and the tile. Therefore, this method is considered as a destructive means of evaluating bond integrity. The National Aeronautics and Space Administration (NASA) is in urgent need to develop a non-destructive evaluation (NDE) technique to survey the bond condition of TPS tiles on orbital vehicles or space shuttles. The novel use of short pulse laser source in conjunction with ultrafast detector and streak camera will provide an alternative new methodology to test the tiles non-destructively without posing any threat to the bond integrity.
Trivedi, A., Mitra, K., and Subramanian, C.S., “Numerical and Experimental Study of Non-destructive Detection of Thermal Tile System Debonding Using Short-Pulse Laser,” AIAA Thermophysics Conference, Portland (Oregon), Paper No. AIAA 2004-2578, June 28-July 1 (2004).