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Upgraded Space Shuttle Discovery Returns to Launch Pad

NASA

Space Shuttle Discovery has returned to Launch Pad 39B after a 10-hour journey from Kennedy Space Center's 52-story Vehicle Assembly Building (VAB), where it recently received an upgraded External Tank with added safety features.

Inside the VAB, orbiter Discovery was removed from its original tank and twin Solid Rocket Boosters (SRBs) and attached instead to External Tank 121 and its pair of boosters. The newer tank -- first intended to fly with Atlantis on STS-121 -- has an additional heater to reduce the potential for ice and frost buildup.

The large, orange External Tank is filled on launch day with super-cold liquid hydrogen and liquid oxygen. It then supplies these propellants to the Space Shuttle's three main engines during the eight-and-a-half-minute climb to orbit.

During an April 14 test, Discovery's original fuel tank was filled with propellants as if on launch day. During the "tanking test," the team evaluated how the tank, orbiter, Solid Rocket Boosters and ground systems performed. The test included a simulated countdown through the T minus 31 second hold.

The test revealed some anomalies, such as engine cut-off sensors that operated intermittently and pressurization valves that opened and closed more often than normal. Therefore, a second test took place on May 20 to gather more data.

"The team went off and wrote an outstanding test plan," said NASA Space Shuttle Program manager Bill Parsons. "We had some special instrumentation that we wanted to put in place so that we could make sure we were getting the right data."

The successful second tanking test was followed by a test of the vehicle's Auxiliary Power Units. Technicians also verified that retract link assemblies on Discovery's landing gear were in good condition following the recent detection of a small crack on one of Atlantis' assemblies. Inspections and photos of Discovery's landing gear assemblies showed the ship's landing gear is free of cracks. The flawed assembly on Atlantis will be replaced with a spare.

Space Shuttle Discovery will carry a crew of seven to the International Space Station during the Return to Flight mission, which has a launch planning window of July 13-31.

Anna Heiney
NASA's John F. Kennedy Space Center