Space shuttle Discovery passes tests as NASA watches for problems with sensor
(Agencies)
Updated: 2005-07-26 20:38

The fuel sensors on Discovery's giant external tank passed initial tests early Tuesday as NASA fueled the spacecraft for the first shuttle flight since the Columbia disaster 2 1/2 years ago.

NASA officials monitored the sensors throughout the three-hour fueling process to make sure they functioned properly. A faulty sensor reading forced NASA to scrub a launch attempt July 13 as the astronauts were boarding the spacecraft.

"All the sensors are performing as expected," said NASA commentator Jessica Rye.

Discovery and its seven astronauts were set to blast off for the international space station at 10:39 a.m. EDT (1439 GMT). The forecast improved early Tuesday, with the chances of good launch weather put at 80 percent, up from 60 percent the day before.

During an early morning meal, crew members sported matching Hawaiian shirts. They smiled for a NASA television camera as astronaut Steve Robinson strummed a guitar. Later in the morning, they waved and gave a thumbs-ups as they walked to the van that took them to the launch pad.

If the equipment trouble reappeared, NASA was prepared to bend its safety rules and press ahead with the launch anyway with just three of the four sensors working.

Only two sensors are needed to do the job. But ever since NASA's return to space in 1988 after the Challenger explosion, the space agency has decreed that all four have to work.

NASA Administrator Michael Griffin called such a deviation from the rules "an acceptable risk."

"Actually, it's quite a low one," Griffin told The Associated Press on Monday.

The fuel sensors are designed to prevent the main engines from running too long or not long enough, in case the fuel tank is leaking or some other major breakdown occurs. An engine shutdown at the wrong time could prove catastrophic, forcing the astronauts to attempt a risky emergency landing overseas, or leading to a ruptured engine.

After Discovery's launch, NASA will take a look at changing the rule to require only three functioning sensors under certain circumstance, Griffin said.

Over the past few days, NASA rewired two of the sensors to try to diagnose the trouble and repaired faulty electrical grounding aboard Discovery in hopes that would solve it. But the space agency was unable to fully explain the faulty reading.

"We have addressed everything we know on the shuttle that can go wrong that we have the technology to fix," Griffin said. "Some things simply are inherent to the design of the bird and cannot be made better without going and getting a new generation of spacecraft."

But a retired agent in NASA's inspector general office, Joseph Gutheinz, said the space agency does not appear to have learned its lesson with Columbia. Accident investigators criticized NASA's tendency to downplay risks and discourage engineers from speaking up.

"It is clear to me that NASA continues to put mission over safety," Gutheinz said. "I fear that if NASA is wrong this time, as they were for Apollo 1, Challenger and Columbia, manned space missions may be halted for a very long time in the United States."

The launch promised to be not only an appraisal of changes in NASA's safety culture, but also a test of the fuel tank that was redesigned after the Columbia disaster to minimize the chances of debris falling off.

Columbia's fuel tank lost a large chunk of foam insulation at liftoff. The debris slammed into the left wing, smashing a hole that proved catastrophic during re-entry February 1, 2003. All seven astronauts were killed.

NASA removed the responsible section of foam and installed heaters in its place to prevent ice buildup from the super-chilled fuel, since flying ice can be as lethal as foam debris. Engineers added a heater in another ice-prone spot on the tank, and a special crew planned to make extra checks for fuel-tank ice during the final portion of the countdown.

A few family members of the fallen Columbia astronauts planned to return for the second launch attempt. The VIP list was topped by first lady Laura Bush and Florida Gov. Jeb Bush, her brother-in-law.

Discovery has only until the beginning of August to fly to the space station on a 12-day supply and repair mission; the next launch opportunity will not come until September 9.

The launch window is dictated by the space station's position and NASA's insistence on a daylight liftoff to provide good views for the more than 100 cameras that will be checking for any Columbia-type launch damage.

While in orbit, Discovery's crew will inspect the most vulnerable areas of the spacecraft, using a new 50-foot (15-meter), laser-tipped boom. They also will practice repairing samples of deliberately damaged thermal tile and panels.

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