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Posted March 30, 2000

UMaine Engineers Test X-38 Aeroshell Panels

In a collaborative project with the National Aeronautics and Space Administration (NASA), a team of UMaine mechanical engineers put panels from the X-38 crew return vehicle through a worst case heat and pressure scenario at Crosby Lab in March.

NASA will use the test results to finalize design specifications for the shell of the space vehicle. When constructed and deployed, the X-38 will function as an emergency lifeboat on the international space station.

NASA is working with Vince Caccese, associate professor of mechanical engineering, and his students to make sure that the graphite aeroshell panels will withstand the rigors of re-entry and get astronauts safely back to Earth.

Caccese coordinates the team which also consists of students Christopher Malm of Caribou, Richard Mewer of Eliot and Josh Walls of Yarmouth.

“We've been working with UMaine engineers to test the structural characteristics of the aeroshell panels for a couple of years through the Maine Space Grant Program,” said Ron Baccus, NASA engineer who came to Orono to help conduct the tests in March. “It's been a very good relationship, and we're very happy with the results.”

“The students did all the calculations on heat transfer and thermal requirements, and they wrote the software that controls the oven,” said Caccese.

Painted UMaine blue, the 15 ft³ insulated oven contains two electric heating elements, four heat lamps and steel blocks that support the panel to be tested. The oven fits on an eight-foot tall pressure testing machine which applies precise forces directly to the panel through the top of the oven.

During the tests, two-foot long panel sections were placed in the oven and heated to 325 degrees Fahrenheit. Increasing force was applied to the panel until it began to break apart. The panels cracked along a glued joint between a curved stiffening element and the flat carbon composite surface.

“This is a worst case scenario,” said Baccus. “Under actual conditions during re-entry, tiles on the skin of the X-38 absorb heat and reflect much of it back into the air. The panels will not be this hot when they are under maximum stress. Nevertheless, we want to be conservative in our design.”

In addition to the tests, Caccese and Malm are using a finite element model to characterize the performance of the panels under various combinations of heat and pressure.

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