NASA has delayed next week's launch of space shuttle Endeavour by one day because of unexpected work to fix a leak in the crew cabin, officials said Friday.

Liftoff is now set for Wednesday evening.

Engineers installed a new valve Thursday to replace a leaky one in Endeavour's crew cabin. Although the unit tested fine, NASA ran out of time to meet a Tuesday launch, said NASA spokesman George Diller.

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Combined with thunderstorms that disrupted work at the launch pad earlier this week, "it just didn't translate into enough time to get there," Diller said. "They were literally trying to put 25 pounds of work in a 10-pound bag."

The replacement valve was taken from Atlantis. NASA has yet to determine what was wrong with the one removed from Endeavour.

Endeavour's one-day postponement gives a little extra breathing room for NASA's Phoenix Mars lander, set to blast off aboard an unmanned rocket Saturday.

The space agency has only three weeks to launch the lander before being forced to wait two years, and officials have indicated they would probably put that flight ahead of Endeavour's.

NASA needs at least two days between rocket launches.

Among Endeavour's seven-member crew to the international space station is Barbara Morgan, the first schoolteacher-turned-astronaut, who was Christa McAuliffe's backup in 1986. McAuliffe was killed aboard Challenger along with six others.