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Gearing up for a Smooth Landing


Pat Dunlap is a list man. He gets personal satisfaction from writing down tasks and crossing them off as he completes them.

"I have pages of to-do lists on my desk, and since we're supporting half a dozen projects it's a way to keep track of them," said the Glenn Research Center Engineer.

As project lead for evaluating the environmental seals on the Space Shuttle's main landing gear doors, Dunlap crossed a major set of to-dos off his list when Discovery landed safely on August 9.

Image of NASA Glenn's award-winning Seal Team.Image left: NASA Glenn's award-winning Seal Team meets in the laboratory they used to perform compression and airflow tests on the Shuttle's main landing gear door seals. Credit: NASA

When NASA installed new seals on Discovery in January, engineers at the Johnson Space Center and the Kennedy Space Center quickly realized that the doors were not closing completely, an unacceptable condition for flight. They turned to Glenn's Seal Team lead Bruce Steinetz and Dunlap for help.

"The seals on the landing gear doors are similar to the ones on a refrigerator or car door," Dunlap explained. "But the Shuttle's seals have to fit perfectly because they protect the landing gear and wheels from hot gases during liftoff and re-entry."

To keep air from leaking in, the seals must fit snugly between the wheel compartments and the doors. But if they are squeezed too tightly, pressure will build in the seals causing them to push back on the doors. That pressure could keep the doors from closing flush against the Orbiter's underbelly.

Dunlap needed to find out how much compression would minimize leakage without putting too much pressure on the doors. So, he added air flow and compression tests to his list of things to do.

Having earned NASA's prestigious Invention of the Year Award for developing a thermal barrier that was used on an Atlas V rocket in 2003, Dunlap and Steinetz are well-known for their expertise in environmental seals.

But it took a team of five, including engineers Jeff DeMange and Josh Finkbeiner and technician Dick Tashjian, to solve this problem. With backgrounds ranging from materials to heat transfer, Dunlap says the engineers and technicians on Glenn's Seal Team strike the perfect balance.

"We each bring our own strengths to the team," he said. "It makes for a really good working group."

Image of main landing gear door seal.Image right: Glenn's Seal Team performed airflow and compression tests on seals like the one pictured. These seals, which are found on the Shuttle's main landing gear doors, protect the landing gear and wheels from hot gases during liftoff and re-entry. Credit: NASA

After months of tests, the team determined that 40-50 percent was the optimum compression level to minimize leakage without putting too much pressure on the doors. They also discovered that excess room-temperature vulcanizing silicone rubber (RTV) was causing increased pressure on the doors. The silicone, which looks similar to the caulking in a bath tub, is used to bond the seals to the doors.

As a result of these tests, engineers removed the extra bonding and built custom shims around the perimeter of the doors to keep compression levels between 40 and 50 percent.

Now that their mission is complete and Discovery has landed safely, the Seal Team will move on to the next big project on Dunlap's list: seals for a new space docking system that will help NASA fulfill the Vision for Space Exploration with journeys to the Moon, Mars and beyond.

More Information:
Read More about Glenn's Return to Flight Efforts

Jan Wittry (SGT, Inc.)
NASA's Glenn Research Center

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