Space Shuttle Heat Shield
Tile Bond Integrity

Early space shuttles had over 24,000 tiles (later models have less) of which a significant number of so called "critical tiles" have to be checked between each and every flight. It was desired to develop a test method which would speed up the maintenance process. Navcon Engineering was contracted by Rockwell (& NASA) to develop a non-contact method to assess the structural integrity of the tiles and demonstrate the method on Space Shuttle Columbia (OV-102).

Columbia (OV-102), NASA's first shuttle orbiter is pictured at Edwards Air Force Base in August of 1981 following Mission STS-40. Navcon engineers were allowed 2 days with the shuttle to demonstrate a non-contact method of evaluating the structural integrity of the thermal protection tiles.

The frequency response of individual tiles was measured by exciting the tile with broadband "white" noise and measuring the surface velocity with a laser vibrometer (as shown in the photograph)The frequency response was computed as velocity/sound pressure. The bond integrity was assessed by noting both the shifts in the resonant peaks and the change in the structural damping. The general method was successful in identifying tiles with bond degradation.