CAPE CANAVERAL, Fla - NASA delayed the launch of space shuttle Atlantis until Sunday at the earliest as managers debated whether to loosen longtime launch rules to get around fuel gauge problems.
Shuttle managers were still meeting late Friday and trying to decide how best to proceed. After six hours of discussion, they had determined it was too late to try for a Saturday liftoff.
Atlantis' countdown was halted Thursday after a pair of gauges at the bottom of the external fuel tank mysteriously failed a routine test at the launch pad.
The day-by-day delay was especially disappointing for the many visitors from the European Space Agency. Atlantis is supposed to carry a huge European-built science lab, Columbus, to the international space station.
Before a launch is allowed, NASA managers must be convinced that flight controllers and the astronauts can safely work around the fuel gauge problem while the shuttle is zooming to orbit.
Since last year, the rule has been that three of the four fuel sensors must be working -- before then, the requirement was four-out-of-four good sensors. But managers were considering further lowering their standards in part because of some new instrumentation added to the shuttle fleet.
NASA has until next Thursday or Friday to launch Atlantis. If it isn't flying by then, the mission will be delayed until January because of computer concerns and unfavorable sun angles for the shuttle when it's docked to the space station.
Engineers suspect the sensors are fine and that the problem is with an open circuit somewhere in the extensive wiring. Any repair would take days.
Each shuttle fuel tank is equipped with four engine-cutoff sensors that keep track of whether the tank is empty or full of liquid hydrogen. The sensors are part of a backup system that would kick in if the tank was leaking during the climb to orbit, for example, and safely shut down the engines. The engines could ignite or explode if they kept running without fuel.
NASA has been bedeviled by these fuel tank sensors ever since 2005, when shuttle flights resumed following the Columbia disaster. Just last year, the space agency eased its sensor rules for launch, requiring only three of the four to be working.
Because of new instruments recently added to the shuttle fleet, flight controllers can tell whether these sensors are working right. If enough sensors failed during liftoff and, possibly, a sizable leak was detected, Mission Control could instruct the astronauts to manually shut down the engines early.
But it's never been given a test run, and it's unknown how much extra risk that would add.
