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Earliest Launch Date for NASA Space Shuttle Is July 26

19 July 2005

Source of fuel-sensor problem eludes teams of engineers

By Cheryl Pellerin
Washington File Staff Writer

Washington -- NASA is targeting July 26 as the earliest possible date to launch the space shuttle Discovery (STS-114) on its return-to-flight mission -- the first shuttle flight in more than two years since the Columbia accident.

At a July 18 news conference from Kennedy Space Center in Florida, space shuttle program manager Bill Parsons announced that troubleshooting on a problem involving one of four sensors in the external tank’s liquid hydrogen tank is continuing around the clock.

The sensors protect an orbiter's main engines by triggering them to shut down safely if fuel runs low unexpectedly.

The sensor circuit failed a routine pre-launch check during the countdown July 13, delaying Discovery’s first launch attempt.

“We’re trying awfully hard to resolve this issue,” Parsons said, “but we have a window that extend[s] from July 13 through July 31 [and] we’re still trying to launch within that window.”

The limits on when Discovery can launch depend on the position in orbit of the International Space Station – Discovery’s destination – and the need to launch the shuttle during daylight hours so multiple cameras can record the liftoff for safety reasons.

A dozen teams, with hundreds of engineers across the country, are working through a troubleshooting plan to find the source of the intermittent sensor problem. The teams have not yet isolated a cause of the sensor circuit failure but have eliminated several possibilities.

They are expected to complete the battery of tests by July 20.

“Our number one goal here is to find this problem and fix this problem,” said Wayne Hale, space shuttle deputy program manager.

SENSOR TESTING CONTINUES; ADDITIONAL PROCEDURES PLANNED

Engineers are testing the sensor circuit in ambient (existing) temperatures and will continue the testing until July 20. If the problem is not found by then, Hale said, the next step is to reload the external tank with super-cooled propellants to see how the sensor circuit behaves at such cryogenic (very low) temperatures.

That procedure (“tanking”), which will take place July 26, could be done as a test or as part of an actual launch countdown.

“There is some debate as to whether we could do the kinds of tests that we need to do at cryogenic countdown and go ahead and launch that day, or whether we need to test, de-tank, recycle [and] think about the data,” Hale said. “That kind of decision is before us.”

“What we’re doing is preserving the [launch] schedule,” Parsons said. If the engineers find the problem, the July 26 tanking test will become the launch, he said. “If we haven’t found anything by then and the technical community comes back and says ... we need to do a tanking test, then the 26th becomes that tanking test.”

Hale said NASA has had a lot of help in its search for the sensor problem.

“The original designer of the point sensor box in the 1970s has come out of retirement and is on our team,” he said.

Offers of help have also come from the Jet Propulsion Laboratory in Pasadena, California, experts from the commercial launch vehicle industry, and the Japanese Aerospace Exploration Agency, which had its own problems with low-level sensors on its H2 rocket.

“We’ve got an amazing team that’s come together to volunteer to work on this problem,” Hale said.

Commander Eileen Collins and her six Discovery crewmates will come out of quarantine July 19 for a day off and will resume quarantine and training later this week.

The health-stabilization quarantine is necessary to ensure that all seven crew members are medically fit for the space mission. Only medically cleared NASA staff and family members can see them before the launch.

Discovery is scheduled for a 12-day flight to deliver equipment and supplies to the International Space Station.

Additional information about the shuttle launch and the International Space Station 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)