Weather permitting, Discovery will lift off from the Kennedy Space Center at Cape Canaveral, Florida, at about 9:18 pm (0118 GMT Thursday).

Discovery's seven astronauts, including Japan's Koichi Wakata, are to deliver the fourth and last pair of power-generating solar panels to the ISS.

Discovery's launch date was announced following Friday's flight readiness review, during which top NASA managers assessed the risks associated with the mission and determined the shuttle's equipment, support systems and procedures were ready for flight.

The launch, originally set for February 12, had been delayed four times due to problems with control valves, which channel gaseous hydrogen from the shuttle's three main engines.

Three of the valves were replaced with newer ones, and NASA engineers said the delays were implemented as a precaution to test the valves, which had come under close scrutiny after a valve aboard space shuttle Endeavour was found to be damaged during its mission to the space station in November.

At a news conference on Friday, Bill Gerstenmaier, an associate NASA administrator, said the review was a very thorough, but "the team came through, worked hard and was efficient."

Space Shuttle Program manager John Shannon said the National Aeronautics and Space Administration now had "definitive data to prove" that the upcoming launch was safe.

"It feels good to be here with a firm launch date," said Mike Leinbach, the space shuttle launch director. "I saw a lot of people after the meeting and the mood is really upbeat."

The extra solar panels are needed to produce enough electricity to conduct all scientific experiments in the new Japanese and European laboratories that were added to the ISS last year.

The ISS crew also wants to invite three more people to join them in May in living full time in space.

"More crew means that we'll have to run more life support equipment, more crew support equipment -- toilet facilities, water processing equipment and all of that stuff," said Kwatsi Alibaruho, the lead space station flight director for the mission. "We'll have to run more of all of that, so we need additional power."

However, installing the new solar panels will not be easy. It will require the installation of a new truss segment sporting solar array wings on the right side of the station.

To perform this task, the station's robotic arm will have to extend its reach to the maximum, leaving it with very little room to maneuver. Four space walks are also scheduled to complete the job.

Discovery will also bring to the ISS a replacement part for a urine recycling machine that was delivered to the station in November, but has not worked yet.

The ISS is scheduled to be completed in 2010, the same target date for the retirement of the US fleet of three space shuttles.

The Discovery crew includes Wakata of the Japan Aerospace Exploration Agency.

After Discovery docks, Wakata will stay aboard the station, becoming the first Japanese station crew member while US astronaut Sandy Magnus will return home.

If the launch date holds, there will be no effect on the next two shuttle launches to the Hubble Space Telescope and again to the ISS, NASA said.

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