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Tuesday, July 26, 2005

Space Shuttle Discovery Is Scheduled for Morning Liftoff - New York Times

Space Shuttle Discovery Is Scheduled for Morning Liftoff - New York TimesJuly 26, 2005
Space Shuttle Discovery Is Scheduled for Morning Liftoff

CAPE CANAVERAL, Fla., July 26 - The shuttle Discovery awaited its return to flight this morning with no sign of the sensor troubles that have bedeviled NASA's last attempt to launch.

At 6:43, the three-hour launch countdown began.

If the launching takes place as planned at 10:39 this morning, it will be the first shuttle flight since the loss of Columbia and its crew of seven astronauts over Texas on Feb. 1, 2003.

The probability that the launch might have to be scrubbed because of local weather conditions has dropped to just 20 percent. NASA rules do not allow launching if none of the three transatlantic landing sites is available in case the shuttle needs to abort because of engine trouble or other problems. One of the sites, in Zaragoza, Spain, has weather that would not allow a landing, but the other two, in Moron, Spain, and Istres, France, were declared acceptable.

The process of filling the shuttle's external tank with 500,000 gallons of liquid oxygen and liquid hydrogen began at 12:48. NASA began monitoring the low-level engine cut-off sensors in the liquid hydrogen tank as soon as they became immersed in the super-chilled liquid. Fueling was completed shortly after 3 a.m.

A malfunction in the fuel level sensor system caused NASA to scrub its first launch attempt, on July 13. The sensors are important because they keep the shuttle's main engines from running on empty -- a situation that could cause them to tear apart, with potentially disastrous results for the shuttle and crew. If two of the sensors indicate the shuttle's tank is nearly empty, they will set off an engine shutdown.

Since the July scrub, 12 teams of engineers from around the country have struggled to address the problem, which first appeared during a test of the tank in April. At that time, NASA officials delayed the launch, then scheduled for May, because of the sensor problem and other issues that had emerged. By June, Discovery had been fitted with a new external fuel tank, many components of the fuel level sensor system had been replaced, and NASA engineers and officials decided that the problem with the sensors had been fixed. They were so confident, in fact, that they decided to forgo another tanking test, in which the tank would be filled with fuel to check the sensors.

Then on July 13, one of the sensors malfunctioned again during a test; mission controllers sent a signal to the sensors to "read dry"--that is, to pretend that there was no fuel in the tank even though they were immersed in it. Three of the four sensors responded correctly, but sensor number 2 failed to change. Just two and a half hours before blastoff, as the Discovery crew members were being strapped into their seats, mission control gave the order to stand down.

At 1:15 this morning, the sensors were once again immersed in liquid hydrogen, and all four sensors "read wet," said Martin J. Jensen, a NASA spokesman. At 1:27, he said, "they commanded them to go dry, and they've all been dry ever since," Mr. Jensen said.

Only two of the sensors need to be functioning in order to properly monitor the fuel levels, but NASA launch rules require that all four sensors be operating. After studying the malfunction for nearly two weeks, NASA officials had decided that if the fuel system failed again in the same way, they would be able to approve a launch with only three sensors working.

The decisions had raised concerns that NASA might be compromising safety in order to launch -- known in the space community as "go fever." The pressure to downplay safety concerns has been cited in the two fatal accidents in the shuttle program's history, the Challenger disaster in 1986 and the loss of Columbia. The independent board that investigated the Columbia accident said that NASA had a "broken safety culture" and called for culture changes to go with the physical modifications that would prevent large pieces of launch debris from causing another fatal accident.

On Sunday, Michael D. Griffin, the agency's administrator, denied that the decision to launch despite the nagging sensor problem was an example of go fever, and said he was "comfortable" with how agency managers were dealing with recent technical problems. The space agency, Mr. Griffin said, is not "brushing away" uncertainty, but dealing with it the way that scientists and engineers do, which is to "balance one type of risk with another type or risk."

"I think what you want coming out of the Columbia accident, the loss of Columbia and the soul-searching examination that NASA has undertaken since then, what you want of NASA is that we make the right technical decisions, that we do the right thing to the extent that we can figure that out, which is hard," he said. "You want us doing what's right and not what's obvious or popular."

The crew -- commander Eileen Collins and her six crewmates - pilot James Kelly, flight engineer Robinson, Soichi Noguchi, Andrew Thomas, Wendy Lawrence and Charles Camarda -- began to enter the shuttle cabin at 7:17, one by one. During the July attempt, many of the crew members took a moment on camera before entering the cabin to hold up banners and send silent signs to family and friends. This time there was less mugging, though Mr. Camarda, who grew up in Queens, N.Y., held up a sign reading, "Hi, Dad." Soichi Noguchi, who is from Japan, waved and held up a sign that, on one side, was a parody of the "get out of jail free" card from the game Monopoly. It read "get out of quarantine free." The other side of the sign said "Out to Launch." He then unfurled a banner of the Japanese Aerospace Exploration Agency.

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