Cape Canaveral, Florida  - US space agency NASA late Tuesday scuttled what would have been its second attempt to launch space shuttle Discovery on a mission to the orbiting International Space Station.

After the risk of lightning forced an overnight launch to be postponed early Tuesday, the blast off was rescheduled for 1:10 am (0510 GMT) Wednesday.

But hours before the new launch attempt, shuttle programme managers announced another cancellation after discovering a problem with a liquid hydrogen fill-and-drain valve in Discovery's aft compartment.

Launch controllers had tried to close the valve, but the device did not deliver electronic confirmation of its closure. Technicians are evaluating whether the valve could be open or partially open.

No new date was immediately set for Discovery to be launched from Kennedy Space Centre in Cape Canaveral, Florida.

The risks for Discovery's seven astronauts and the shuttle were too high Tuesday, NASA Director Pete Nickolenko said. Lightning was still visible in the skies over Cape Canaveral as the launch time approached.

"If we had 30 more minutes to go I think we would have a real good shot," said NASA technician Mike Moses.

However, Discovery did not have that extra time due to a limited time window for the takeoff.

Delayed takeoffs are common with space shuttle missions. The last shuttle to blast off, Endeavour, only did so in July after five scrubbed missions due to technical problems and bad weather.

The current planned 13-day mission is designed to transport new equipment and experiments to the International Space Station (ISS). Astronaut Nicole Stott is expected to relieve Timothy Kopra aboard the ISS, and three spacewalks are planned for the mission.

Discovery's crew for this mission includes six Americans and Swede Christer Fuglesang, flying for the European Space Agency. (dpa)