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NASA Managers Target May for Next Shuttle Launch

01 March 2006

Engineers working to reduce insulating foam loss from external tank

By Cheryl Pellerin
Washington File Staff Writer

Washington – NASA managers are targeting a May launch window for space shuttle Discovery’s flight to the International Space Station, and say the engineering team is working an “aggressive schedule” to reduce the loss of insulating foam from the orbiter’s external tank during takeoff and tackle other issues.

Other technical work to be completed before Discovery flies includes a series of wind tunnel tests to confirm the preliminary engineering analyses of the aerodynamics of the redesigned external tank, and replacing ceramic-coated gap fillers that provide a cushion between the orbiter’s protective heat shield tiles.

“The thing that is going to pace getting Discovery off the ground,” said Space Shuttle Program Manager Wayne Hale at a February 28 briefing, “ ... is the engineering analysis and tests that go toward proving that what we’ve assembled on the launch pad is safe to fly.”

The launch window for Discovery is May 3-22. The next launch opportunity after that is July 1-19.

“One of the real challenges we had on STS-114 [Discovery’s 2005 flight] was the gap fillers that came out from between a couple of tiles that caused us some concern.” Hale said.

Each orbiter has 15,800 gap fillers, and NASA managers have made a commitment to replace at least 4,000 for the first flight of each orbiter.

“We’re just about finished with that work on Discovery,” he added, “and we’re getting ready to start work on Atlantis and then Endeavor.”

EXTERNAL TANK REDESIGN

For the external tank, the wind tunnel tests and analyses are needed because the external tank has undergone many major safety changes, including removal of the protuberance air load (PAL) ramps, which consist of thick, manually sprayed-on layers of foam.

The ramps were on the tank to protect a cable tray and two pressurization oxygen and hydrogen lines during the dynamic portion of launch, which includes liftoff through about the first three minutes of the climb to orbit.

The ramps were the source of a 0.45-kilogram (1-pound) piece of foam that came off Discovery’s external tank during its 2005 launch. The foam did not hit the orbiter.

In 2003, a piece of insulating foam weighing less than 0.9 kilograms (2 pounds) struck the orbiter during launch and caused the Columbia accident in 2003 during the orbiter’s re-entry into Earth’s atmosphere.

The ramps were removed to help eliminate potentially damaging debris.

The redesigned external fuel tank arrived at NASA's Kennedy Space Center in Florida March 1 on a barge from NASA’s Michoud Assembly Facility near New Orleans.

At Kennedy, the tank will receive a final inspection and eventually be attached to the twin solid-rocket boosters and Discovery for its mission (STS-121) to the International Space Station.

The tank feeds 535,000 gallons of liquid hydrogen and oxygen propellants to the shuttle's three main engines, which power it to orbit.

There are two PAL ramps on the external tank – one at the top of the liquid oxygen portion of the tank, which is 4.2 meters long and consists of 6 kilograms of foam.

The other is a liquid hydrogen PAL ramp, which is 11.5 meters long and contains 9.5 kilograms of foam.

Wind tunnel testing of the external tank aerodynamics is scheduled to begin in mid-March and continue through April.

Hale said foam still would come off the external tank during launch, but the pieces will be small – most of them less than 28 grams (1 ounce) and smaller than a matchbox – and would not cause damage if they strike the orbiter.

Even smaller pieces, “what we call popcorn,” Hale said, which are about the size of a pencil eraser, have been coming off the external tank for years and pose no threat to the orbiter.

DISCOVERY’S MISSION

Discovery’s mission, the second in NASA’s return to flight series, was supposed to be a logistics and resupply mission to the International Space Station.

Instead, Hale said, the shuttle crew also must help repair an umbilical system cable, one of two that provides power, data and video to the mobile transporter.

The mobile transporter is a flatcar-like movable base on a track that allows the Canadarm2 robotic arm to move nearly 91.4 meters along the space station complex for maintenance and assembly.

“Because of the failure of the trailing umbilical system,” Hale said, “they are frankly crippled in the robotic operations today on the International Space Station and we have a vital new task that we’ve got to perform in STS-121 ... to re-enable the robotic systems on the International Space Station and support the next assembly flights.”

Discovery’s seven-member crew also will test new equipment and procedures designed to increase the safety of shuttles and deliver supplies.

More information about the next Discovery mission is available on the NASA Web site.

(The Washington File is a product of the Bureau of International Information Programs, U.S. Department of State. Web site: http://usinfo.state.gov)