Shuttle passes first Nasa test before launch
A fuel sensor system on Discovery’s external tank passed its first test early today as Nasa began fuelling the space shuttle for the first launch attempt since the doomed Columbia flight two and a half years ago.
Nasa officials monitored the fuel sensor system on the gigantic external tank throughout the three-hour fuelling process and planned to conduct two other tests to make sure the sensors functioned properly.
A faulty reading of a sensor caused the launch to be scrapped on July 13 as astronauts were boarding the spacecraft.
“All the sensors are performing as expected,” Nasa commentator Jessica Rye said after the first test.
Discovery and a crew of seven were set to blast off for the international space station at 10.39am local time (3.39pm Irish time). The threat of storm clouds put the odds of good launch weather at 60%.
Nasa had the paperwork ready to go in case the equipment trouble reappeared and the space agency’s managers decided to press ahead with the launch with just three of the four sensors working – a deviation from a rule instituted after the 1986 Challenger explosion.
Only two sensors are needed to do the job. But ever since Nasa’s return to space in 1988, the space agency has decreed that all four have to work to proceed with launch.
Nasa administrator Michael Griffin called the deviation “an acceptable risk.”
“Actually, it’s quite a low one,” Griffin said.
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.
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.
“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 criticised 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 US.”
The launch promised not only to be an appraisal of changes in Nasa’s safety culture, but also a test of a redesigned fuel tank that was altered after the Columbia disaster to minimise debris falling off it.
Columbia’s fuel tank lost a large chunk of foam insulation at lift-off. The debris slammed into the left wing, smashing a hole that proved catastrophic during re-entry on February 1, 2003. All seven astronauts were killed.
Nasa removed the responsible section of foam and installed heaters in its place to prevent ice build-up 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 Governor 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 lift-off 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 laser-tipped boom. They also will practice repairing samples of deliberately damaged thermal tile and panels.
