NASA began fueling the shuttle at about 6 a.m., hoping that the gauges in its big external tank would work properly and allow launch controllers to proceed with an afternoon liftoff.
Shuttle managers said they would halt the countdown and call everything off if any of the four hydrogen fuel gauges acted up. Three failed during Thursday's launch attempt; no one knows why.
Officials insisted Saturday that all four of the gauges would have to be working on Sunday to move ahead with a launch.
Not only do all four of Atlantis' fuel gauges have to work — until now, only three good gauges were required — a new instrumentation system for monitoring these gauges also has to check out well. What's more, NASA has shrunk its launch window from five minutes to a single minute for added safety.
NASA began draining fuel from the shuttle's tanks Sunday morning, and officials would spend the day trouble shooting the problem. There was no word yet on when another attempt would take place.
"In a way this could be a good thing," said NASA spokesman George Diller, adding that it "may very well help us get to the bottom of this problem."
The troublesome gauges, called engine cutoff sensors, are part of a backup system to prevent the shuttle's main engines from shutting down too late and running without fuel, a potentially catastrophic situation. They have been a source of sporadic trouble ever since flights resumed in 2005 following the Columbia tragedy.
With no idea what is causing the fuel gauges to fail every so often, any repairs would take days if not weeks. As a result, senior managers decided Saturday to alter its launch rules for this mission only, in hopes of getting Atlantis off the ground as soon as possible.
If the shuttle isn't flying by week's end, the mission will be delayed until January because of unfavorable sun angles and computer concerns.
Two groups of NASA engineers recommended that the flight be postponed and the fuel gauge system tested, to figure out what might be going on. But they did not oppose a Sunday launch attempt when it came time for the final vote.
Shuttle commander Stephen Frick was deeply involved with the decisions that were made, officials said.
Both the astronauts and flight controllers would have an added burden if multiple fuel sensors were to fail once the shuttle lifted off and a leak or some other serious trouble cropped up during the 8 1/2-minute climb to orbit. They would have to override the system, and hobble to orbit or make an emergency landing.
Frick and his six crewmates — one of them French, another German — are set to deliver and install the $2 billion Columbus laboratory at the space station. It will be the second lab added to the orbiting outpost and Europe's entree to daily, round-the-clock scientific operations with astronauts in space.
Güncelleme Tarihi: 10 Aralık 2007, 11:31