(Agencies)
Updated: 2007-12-09 21:58

Cape Canaveral - NASA called off Sunday's planned launch of the space shuttle Atlantis after a gauge in a fuel tank failed for the second time in four days.

Space Shuttle Atlantis is seen at pad 39A at the Kennedy Space Center, Fla., December 8 2007. NASA managers are meeting to determine if they will launch Atlantis Sunday with the malfunctioning sensors inside the external tank. [Agencies]

It was not immediately clear when NASA might try again to send Atlantis to the international space station. Senior managers planned to meet later Sunday to decide on a course of action.

The problem with the fuel gauge resurfaced just before sunrise, about an hour after the launch team began filling Atlantis' tank for an afternoon liftoff.

Shuttle managers had 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.

"This could all be good news because it may give us some data points that we did not have as to what may be behind this problem," said NASA spokesman George Diller.

"So essentially our launch attempt this morning has turned into a tanking test," he added.

If the shuttle isn't flying by Thursday or possibly Friday, it will have to wait until the beginning of January to deliver a new laboratory to the space station -- assuming the fuel gauge problem can be fixed by then.

Despite objections from some engineers, NASA tightened up its launch rules for Sunday's attempt in hopes of getting Atlantis off the ground by the week's end.

Not only did all four of Atlantis' fuel gauges have to work on Sunday -- until now, only three good gauges were required -- a new instrumentation system for monitoring these gauges also had to check out. NASA also shrank its launch window from five minutes to a single minute for added safety.

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.

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.