Good weather looks 70 percent likely for Monday's scheduled launch of Endeavour, the next-to-last U.S. space shuttle mission as NASA develops a new generation of craft for longer voyages.
Liftoff is set for 8:56 a.m. EDT (1256 GMT) from the Kennedy Space Center for the trip to the International Space Station after the U.S. space agency repaired a technical glitch that canceled last month's launch attempt.
Endeavour and its six-man crew will deliver a unique astronomical and particle physics experiment to the orbiting outpost. The $2 billion Alpha Magnetic Spectrometer is designed to illuminate dark matter and other exotic forms of nature that so far have eluded scientists' grasp.
The crew is led by Mark Kelly, the husband of U.S. Representative Gabrielle Giffords who is expected to watch the launch as she recovers from a gunshot wound to the head from an assassination attempt in January.
The 16-day mission includes four spacewalks -- the last ones by shuttle astronauts -- to help get the space station ready for operations after the shuttle fleet is retired. The 135th and final shuttle launch is scheduled for early- to mid-July aboard Atlantis.
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NASA tried to launch Endeavour on its 25th and final flight on April 29 but stopped the countdown after a heater in one of the shuttle's onboard power generators failed.
Technicians traced the problem to a short circuit in an electronics box that apparently was caused by the heater's thermostat, which had been inadvertently damaged during a routine test, said shuttle mission manager Mike Moses.
Because of the delay, the shuttle and space station crews will have to work in two shifts.
Normally, the visiting astronauts and their hosts work and sleep on the same shift. But because half of the station crew is leaving on May 23 to return to Earth, it was not possible to synchronize their schedules with the shuttle crew, NASA managers said.
Meteorologists said there was a 70 percent chance the weather would be acceptable for launch.
Giffords, an Arizona Democrat who has not been seen in public since the shooting in January that killed six people, was scheduled to travel to Florida on Sunday.
She met President Barack Obama and his family at the Kennedy Space Center before the last attempt in April. Obama is not returning for Monday's attempted launch.
As NASA workers ramped up for Endeavour's launch on the 134th shuttle mission, prime contractor United Space Alliance mailed out layoff notices to half of its employees.
"The mood is a little bit downcast right now but I have no worries at all about the team being able to make the right calls on Monday," said NASA launch director Mike Leinbach.
United Space Alliance is a joint venture equally owned by Boeing Co and Lockheed Martin Corp.
NASA is ending the 30-year-old shuttle program due to high operating costs and to develop spaceships that can travel to asteroids, Mars and other destinations where the shuttles cannot go.
After the shuttles are retired, Russia will operate the only crew flights to the space station until private firms are able to fly people into orbit, which is expected to take four to five years. NASA is turning over cargo flights to the station to two commercial operators.
