Tests helping to solve riddle of tile damage

The vivid images of foam coming off the external tanks of Space Shuttle Columbia during ascent reminded the world that human space flight can be dangerous. As NASA and its team of contractors get ready for return to flight this fall, one of their priorities is to understand better the impact of debris on the Space Shuttle tiles.

Shawn Sorenson, Boeing IDS tile-testing project engineer and coordinator, sees the results of tile testing every day at the foam test center at Southwest Research Institute in San Antonio. One of the recommendations of the Columbia Accident Investigation Board investigation was to improve the capability to assess what damage debris such as ice or insulating foam from the external tank could inflict on the orbiter.

"We vary the angle, speed and the location for each debris strike test on the tile and understand the physics from these different impacts," Sorenson said. "The goal of the test program is to provide data for improved computer models to predict damage from debris strike."

Southwest Research Institute uses large, medium and small compressed-gas guns to fire foam samples at speeds from 200 feet per second to around 1,500 feet per second, with varying angles of incidence from 10 to 90 degrees.

Sorenson got started with the tile-testing program in October and planned the first tests that began in November. With nearly 1,000 test shots on tile planned, the testing is expected to last until early June.

The program also includes tests, already under way, on ice, metal and ablators at NASA sites at the White Sands Test Facility in Las Cruces, N.M., and Kennedy Space Center, Fla. Sorenson spends time at each test site while jumping back and forth as needed to his office in Houston.

The orbiter stress group is developing a suite of analytical models based on these test results, Sorenson said. His job: Help run the test program and make sure the test facilities have all the necessary materials and resources, and serve as an interface between the test facilities and the analysts that are using the test data to build their models.

"I really like the big-picture aspect of the tile testing," Sorenson said. "Having spent some time in both thermal and stress analysis, I like the multidisciplinary approach I get in doing something like this."

Special tests have also been conducted on tile configurations that represent main landing gear door edge tile area and carrier panel tiles (the tiles located underneath the Reinforced Carbon-Carbon panels near the wing leading edges).

"We are doing a lot of testing in a short period, and there has been a tremendous effort, such as these special configuration tests at Southwest Research Institute. It is more challenging to pull off one of these special configuration tests than the normal tile tests," Sorenson said. "We managed to do six tests in four days. That's a tremendous effort that epitomizes the dedication of everyone involved."

-Ed Memi