U.S. space shuttle ready to deliver Japanese porch

CAPE CANAVERAL, Florida (Reuters) - NASA prepared to launch space shuttle Endeavour to the International Space Station on Saturday to deliver a Japanese porch and spare parts needed to keep the outpost going after the shuttle fleet's retirement next year.

The space agency planned to begin fueling the ship just after 10 a.m. for liftoff from the Kennedy Space Center in Florida at 7:39 p.m..

NASA tried twice last month to launch Endeavour, but was stymied by potentially dangerous hydrogen fuel leaks.

Engineers discovered a misalignment in a line that vents hydrogen from the fuel tank as it is being filled. Technicians made repairs and tested the work last week.

"I have extremely high confidence" in the repair, said Mike Moses, who oversees the shuttle program at the Kennedy Space Center.

The only issue may be the weather. Meteorologists on Friday predicted a 60 percent chance that thunderstorms and rain would be too close to the launch site for Endeavour to fly.

"I don't worry about things I can't control and I certainly can't control the weather," Moses said.

NASA is running out of time to finish the station and retire the shuttle fleet by September 30, 2010, as directed by Congress. Managers say they will not compromise safety for schedule and will ask for an extension and more funding if necessary to complete the outpost, a $100 billion project of 16 nations.

Including Endeavour's mission, the agency plans eight more flights to the station. After the shuttles are retired, U.S. astronauts will fly on Russian Soyuz capsules and cargo will be delivered by Russian, European and Japanese vehicles.

The station has been under construction 225 miles above Earth for more than a decade. It consists of nearly 26,000 cubic feet of pressurized space, about as much room as a typical four-bedroom house.

Endeavour carries the last parts for Japan's elaborate three-part Kibo laboratory, including an open porch to expose science experiments to the space environment.

"It's really an exceptionally valuable piece of real estate," Endeavour astronaut David Wolf said in a prelaunch interview. "It has its own robotic arms, the ability to do observations of the Earth and of the sky, astrophysics experiments, a very wide range of abilities."

The platform will be attached to the front of Japan's $2.4 billion Kibo complex during the first of five spacewalks planned during Endeavour's 12-day stay at the station.

One of the Endeavour astronauts, Timothy Kopra, will remain aboard the station, taking over the flight engineer's post from Japan's Koichi Wakata, who has been in orbit since March.

Wakata is scheduled to return with the Endeavour crew -- commander Mark Polansky, pilot Douglas Hurley, spacewalkers Wolf, Christopher Cassidy, Thomas Marshburn and Canadian flight engineer Julie Payette -- on July 27.

(Editing by Jim Loney and Peter Cooney)