CAPE CANAVERAL, Fla. - Space Shuttle Endeavour's Earth-mapping mission is off until February 9 -- and perhaps longer -- so workers can replace a crucial signal relayer that failed during a scrubbed launch attempt Monday.

Mission managers ordered the stand-down early Tuesday after engineers tried fruitlessly to duplicate the problem during testing overnight.

"They're pretty sure there's something wrong with it," said George Diller, a spokesman with NASA's Kennedy Space Center (KSC). "They can't get it to repeat the problem. There's something down in there that's not right."

Mission managers had counted on replicating the problem during overnight testing. Doing so was considered critical to clearing Endeavour for a launch attempt at 12:44 p.m. Eastern Standard Time Tuesday.

"We're concerned that we will never be able to duplicate it," shuttle program manager Ron Dittemore told reporters here at KSC. "That's our greatest fear, that we can't find [the problem] and don't understand it."

The decision to delay was a no-brainer: The inability to pinpoint the problem means engineers cannot guarantee that the balky signal relayer will work during flight. It plays an absolutely critical role during a shuttle's eight-and-a-half minute climb to orbit.

Endeavour is outfitted with two of the relayers. Slightly bigger than household VCRs, the devices route computer commands needed to ignite a shuttle's twin solid rocket boosters and then jettison them two minutes into flight. The so-called Master Events Controllers also route commands needed to separate the shuttle from its 15-story external fuel tank shortly after the ship reaches orbit.

Managers ordered the replacement of the suspect relayer. That work is expected to take at least five to six days. The soonest NASA could be ready to launch the shuttle would be February 9.

Now, both NASA and the Boeing Co. are requesting that date -- NASA for the Endeavour launch, and Boeing for a commercial satellite delivery mission aboard a Delta rocket. Negotiations are ongoing.

Meanwhile, Endeavour's six astronauts -- four men and two women -- will return to Houston's Johnson Space Center Wednesday to continue training while Endeavour is fixed. The astronauts would return to the Kennedy Space Center on Saturday if NASA secures the February 9 launch date. The three-day countdown would begin on Sunday.

The international crew, which includes an astronaut each from Japan and the European Space Agency, are to fly an 11-day mission to collect data for the most detailed 3-D map ever made of Earth's surface features.

Engineers had scrambled throughout the night to get the signal relayer to repeat the problem that cropped up during Monday's countdown. The device had first given out the wrong signal and later corrected itself for reasons that are unclear to NASA.

"Unfortunately when you deal with avionics, many times it is hard to duplicate what caused the problem," Dittemore said. "Sometimes these things happen."

Dittemore compared the dilemma to a situation faced by just about anyone who works with computers: a hung-up machine.

"That's why you and your personal computer do a re-boot, because you don't know what happened," he said. "So you know if you just recycle, it comes back up and it just seems to work until the next re-boot."

The "re-boot" in NASA's case, he said, means simply switching out the bad signal relayer.