NASA aims to launch shuttle on Sunday

CAPE CANAVERAL, Florida (Reuters) - NASA rescheduled the launch of space shuttle Discovery for Sunday after a fuel leak scuttled its first launch attempt on Wednesday, officials said.

Liftoff is set for 7:43 p.m. EDT (11:43 a.m. British time) from the Kennedy Space Centre in Florida.

The purpose of the flight -- the first of five planned for this year -- is to deliver a final set of solar power panels to the International Space Station and transport Japan's first astronaut to serve as a member of the live-aboard station crew.

Wednesday's launch attempt was called off while the shuttle was being filled with liquid hydrogen and liquid oxygen for the ride to orbit.

"We're sure that we have some hardware issues there," said shuttle launch director Mike Leinbach.

The leak appeared around a vent valve that releases hydrogen gases that have boiled off during the fill-up.

Discovery's mission had already been delayed a month due to safety concerns about fuel pressure valves, but after extensive testing and studies, managers cleared the ship for flight.

Wednesday's fuel leak was unrelated to the valve issue, NASA officials said.

The shuttle is to spend two weeks in orbit to deliver a $300 million (217 million pounds) set of solar wing panels and a new distiller for the station's urine recycling system.

The panels are inside a 16-tonne module that will complete the station's 11-segment exterior backbone.

The seven-man crew includes Japan's Koichi Wakata, a two-time shuttle veteran who will stay behind on the space station to serve as a flight engineer after the shuttle departs. He replaces NASA astronaut Sandra Magnus, who has been in orbit since November.

The station, a $100 billion project of 16 nations, has been under construction 220 miles (350 km) above Earth for more than a decade.

The U.S. space agency has up to nine flights remaining to complete assembly, as well as a final servicing call to the Hubble Space Telescope, before it retires the shuttle fleet next year.

(Editing by Jim Loney and Mohammad Zargham)