A week before Endeavour's planned liftoff, NASA was analyzing a cabin leak in the space shuttle Tuesday.

Canadian astronaut Dave Williams is scheduled to take three spacewalks during the Endeavour mission. NASA is analyzing a cabin leak in the space shuttle one week before it is supposed to launch.
(David J. Phillip/Associated Press)

The leak was detected over the weekend. NASA thought it fixed the problem by tightening a loose bolt, but testing Monday night confirmed air was still escaping from the crew cabin, said NASA spokeswoman Tracy Young.

Engineers have yet to pinpoint the leak, which could require so much work that NASA might not be able to launch Endeavour on Aug. 7.

NASA's planned launch of the Mars lander Phoenix later this week could also interfere with Endeavour's flight. The Phoenix has only three weeks in which to launch before facing a two-year wait, and the mission already was pushed back from a Friday launch to Saturday because storms delayed rocket preparations.

Space agency officials have indicated they want the Mars craft on its way before Endeavour gets a turn at launching.

Making the trip to the International Space Station aboard the shuttle is school teacher-turned-astronaut Barbara Morgan, who was Christa McAuliffe's backup in 1986. McAuliffe was killed along with six others when the Challenger broke up shortly after liftoff.

The crew also includes Canadian astronaut Dave Williams, who is scheduled to take three spacewalks, one more than any Canadian before him.

The shuttle crew will work to complete assembly of the orbiting space station, installing the third starboard truss segment, a 2,200-kilogram piece that is a key building block in the station's solar panel array.