Computer trouble and bad weather forced NASA on Monday to delay the launch of space shuttle Endeavour on a quest to create the most accurate map of Earth ever produced.
Launch managers said they would try again today, but only if the computer problem can be solved quickly. Liftoff time would be 12:44 p.m.
"If we don't understand it to the point where we know we are safe then we will not launch," shuttle program manager Ron Dittemore said. "We can always take the time to change out the box."
Dittemore said the launch would have to be delayed a week in order to replace the computerized unit, called a master events controller.
It is a critical component. Two identical controllers are on board, and both are needed to send signals to ignite the two solid rocket boosters at liftoff and to later separate the boosters and external fuel tank from the shuttle.
The mission is already four months late because of damaged wiring that had to be fixed on Endeavour and the other shuttles.
The computer trouble cropped up with less than a half-hour remaining in the countdown. Even without the problem, Endeavour could not have lifted off because of rain and thick, dark clouds.
NASA went all the way down to the nine-minute mark as engineers scrambled to understand why one of the two controllers sent a series of erroneous signals during a pre-launch check. The unit worked well when engineers repeated the test, but no one could explain the earlier malfunction.
"Sometimes these things happen, and we're concerned that we will never be able to duplicate" the error, Dittemore said. "That's our greatest fear, that we can't find it and don't understand it."
Just the day before, NASA cleared Endeavour for launch after an exhaustive review of seals in its three engine fuel pumps.
A defective seal meant for the trash somehow ended up in a fuel pump used by Discovery during its Dec. 19 launch. NASA wanted to make sure no factory rejects were in Endeavour's pumps.
Because of missing paperwork, NASA could not verify that two of Endeavour's seals were certified for flight. Nevertheless, NASA proceeded toward a launch.
Endeavour is carrying radar that will survey most of the Earth's terrain.
If all goes well, the result will be the most complete and accurate topographic map of the world.