Thermal Testing Techniques for Space Shuttle Thermal Protection System Panels

An experimental system was developed at the McDonnell Aircraft Company, McDonnell Douglas Corporation, for evaluation of the effects of aerodynamic heating and cooling, vacuum, and pressure loading on candidate insulation packages proposed for use on the Space Shuttle. The system includes a number of design features which facilitate rapid recycle times. This is necessary to efficiently conduct extensive thermal cycling tests on these insulation packages to determine their reuse capabilities. The heart of the system is a 26-inch x 26-inch graphite element radiant heater. A susceptor plate functions as a uniform-temperature intermediate radiating
surface. The susceptor also forms the lid of an inert atmosphere enclosure which separates the heater from the oxidizing test atmosphere. In some tests the plate properly simulates the heating from an actual flight heat-shield panel. Although other materials were used at lower required test temperatures, 2500°F was
routinely achieved using a coated columbium susceptor plate. Since vibration and acoustic testing were to be performed in conjunction with the thermal cycling, we designed special specimen holders that were easily removable for alternate mounting in the desired test apparatus. This allowed rapid turnaround time between various tests without any damage incurred from specimen handling. One of the specimen holders would accept up to five insulation packages at a time. This increased the number of candidate insulations which could be screened in a given time.

In the first 6 months of operation nearly 300 thermal cycles, including 200 cycles using the coated columbium susceptor plate, have shown no significant problems in the system.