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Faulty Sensor Makes NASA Delay Shuttle Launch

July 13, 2005

CAPE CANAVERAL, Fla. — A fuel gauge that mistakenly read full instead of empty forced NASA to call off Wednesday’s launch of the first shuttle flight in 2 1/2 years, a bitter disappointment to the space agency in its bid to recover from the Columbia tragedy.

The launch was delayed until at least Saturday, and the postponement could last much longer depending on the repairs needed.

Shuttle managers said it was unclear whether Discovery could be fixed at the pad or would need to be returned to the hangar for more extensive repairs. They expected to have a better idea on Thursday.

A similar problem cropped up intermittently during a fueling test of Discovery back in April. The external fuel tank, along with cables and other electronics, were replaced, and even though NASA could not explain the failure, it thought the problem was resolved and pressed ahead with launch.

At a news conference of grim-faced NASA officials, deputy shuttle program manager Wayne Hale defended that decision.

“We felt like we had a good system,” he said.

“We became comfortable as a group, as a management team, that this was an acceptable posture to go fly in,” he added, “and we also knew that if something were to happen during a launch countdown, we would do this test and we would find it. And guess what? We did the test, we found something and we stopped. We took no risk. We’re not flying with this.”

The seven astronauts had barely climbed aboard Discovery for their journey to the international space station when NASA halted the countdown with less than 2 1/2 hours to go. Up until then, the only threat to NASA’s first mission since the 2003 Columbia disaster was thunderstorms.

“Appreciate all we’ve been through together, but this one is not going to result in a launch attempt today,” launch director Mike Leinbach informed his team.

NASA has until the end of July to launch Discovery; otherwise it must wait until September. The launch windows are dictated by both the position of the space station and NASA’s desire to hold a daylight liftoff in order to photograph the spacecraft during its climb to orbit.

When the shuttle finally takes off, the astronauts will test new techniques for inspecting and repairing cracks and holes similar to the damage that doomed Columbia.

Thousands of people had descended on the space center for the launch, including John Glenn, the first American to orbit the Earth, members of Congress, and family members of the seven fallen Columbia astronauts. Lawmakers and others refrained from second-guessing NASA’s decision to press ahead before it had gotten to the bottom of the fuel gauge problem.

“I’m disappointed for all of us,” said Sen. Bill Nelson, D-Fla., who as a congressman was on the shuttle right before the 1986 Challenger launch explosion. But he added, “The system is working like it should.”

Just a day earlier, NASA was embarrassed when a lightweight plastic window cover fell off the shuttle on the launch pad and caused damage to some of its thermal tiles – the very thing that NASA had worked so hard to avoid after Columbia’s wing was pierced at liftoff by a chunk of foam insulation from the fuel tank. Discovery’s tiles were quickly replaced.

Since the Columbia tragedy, NASA has worked to fix its “safety culture,” which the accident investigators concluded broke down during the flight. The space agency said it has had frank and vigorous discussions about the upcoming flight – including the fuel gauge problem – and encouraged engineers to speak up.

In the 2 1/2 years since Columbia broke apart during re-entry, NASA has concentrated on making the external fuel tank safer by reducing the risk that foam insulation, ice or other debris will break off at launch. The gauge that caused trouble on Wednesday is located in the external fuel tank, but was unrelated to any of the safety modifications.

The faulty gauge reading cropped up after the tank was filled with more than 500,000 gallons of liquid hydrogen and oxygen. Launch controllers ran a test to check out all four hydrogen-fuel gauges in the tank; when they sent a command mimicking an empty tank, three indicated empty, while one stayed stuck on full.

It was a clear violation of the launch rules, Hale said, and it took just five minutes of discussion for managers to agree on a postponement.

NASA requires all four hydrogen sensors to be working to ensure that the main engines shut off at the precise moment in space. If the engines shut down too soon or too late because of an erroneous gauge reading, the results could be catastrophic. For instance, the engines could rupture if they kept running after the tank sprang a leak and ran out of fuel.

After the April malfunction, NASA replaced Discovery’s fuel tank because of unrelated concerns about dangerous ice buildup. Technicians also replaced cables and electronics equipment aboard Discovery itself that are associated with the fuel gauges.

Shuttle program manager Bill Parsons stressed that it was not clear whether the problem was with the fuel gauge itself, or with other electronics aboard the spacecraft.

NASA is looking closely at the possibility that flawed transistors in an electronic “black box” aboard Discovery might be to blame. The box used in the April test also had bad transistors, and when it was removed from the shuttle, the problem disappeared. Managers suspect a manufacturing defect with these transistors.

Parsons nixed a fueling test of Discovery’s replacement tank in June over the protests of some engineers. Such a test would have pushed the flight later into July, and Parsons and others maintained that the ultimate test would come on launch day. Moreover, Hale said there was no guarantee the malfunction would have turned up during a tanking test.

The issue came up again at launch readiness reviews earlier in the week and, to everyone’s satisfaction, was deemed an “unexplained anomaly,” Hale said.

The launch scrub cost NASA an estimated $616,000 in fuel and labor costs.

The Mission

The flight of space shuttle Discovery will be NASA’s first since the Columbia accident in February 2003. Some details of what will be the 114th shuttle mission:

Destination: International space station.

Mission: To test and evaluate new shuttle safety measures, including inspection and repair techniques. There will be three spacewalks to test some of the new repair methods and to replace broken space station parts. The shuttle will also deliver supplies to the space station and haul away old equipment and trash.

Duration: 12 days, with liftoff originally set for July 13 and landing for July 25. The July 13 launch was postponed due to a faulty fuel gauge.

Spacecraft: Discovery made its maiden voyage in 1984 and was also the first shuttle to return astronauts to space after the Challenger disaster in 1986. It is now NASA’s oldest shuttle. This will be its 31st flight.

Crew: Seven astronauts, one of those from the Japanese Space Agency. The commander is Eileen Collins, who in 1999 became the first woman to command a U.S. space mission.

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On the Net:

http://www.nasa.gov


Faulty Sensor Makes NASA Delay Shuttle Launch Faulty Sensor Makes NASA Delay Shuttle Launch Faulty Sensor Makes NASA Delay Shuttle Launch Faulty Sensor Makes NASA Delay Shuttle Launch


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