The space shuttle Endeavour (STS-127) is seen at the Kennedy Space Center in Florida in advance of a July 15 launch. Forecasters said nearby thunderstorms, forced Nasa to scrub Monday's launch attempt. -- PHOTO: AFP

CAPE CANAVERAL (Florida) - THE lightning storms and tank problems that have blighted five attempts to launch the space shuttle Endeavour will leave cash-strapped NASA footing US$4.5 million (S$6.5 million) in extra costs, the US space agency said.

Along with the cost of filling, draining and then refilling the external tanks so many times with specialised liquid hydrogen and oxygen fuel, the cost is also boosted by overtime pay for Nasa employees and other workers at the space centres here.

The overall US$4.5 million cost provided by information from Nasa is 'marginal' in Nasa's overall operating budget, added Mr Beutel. The agency says the space shuttle Endeavour alone, built to replace the shuttle Challenger, cost some US$1.7 billion.

The weather has been blamed for scuttling chances to launch Endeavour in recent days, but Nasa has promised a sixth attempt late Wednesday to reach the International Space Station mission.

The shuttle is now set to lift off at 6.03pm on Wednesday (2203 GMT, 6.03am Thursday) from Nasa's Kennedy Space Centre at Cape Canaveral, Florida, with the US space agency saying there is only a 40 per cent chance of unfavourable weather conditions this time.

A launch was also being considered for Thursday, the last possible date before interfering with the July 24 lift-off of the Russian cargo craft Progress to the ISS, launch integration manager Mike Moses told reporters.

Although Russian space officials have accepted the Thursday launch option, Moses noted that it would force NASA to abort the fifth spacewalk planned for Endeavour's mission to the ISS.

If the shuttle does not take off on Wednesday or Thursday, the next launch window would begin on July 26. Forecasters said nearby thunderstorms, forced Nasa to scrub Monday's launch attempt.

'Again, the vehicle and our team were ready, but the weather has just bitten us again with the lightning within 20 nautical miles (37km)', said launch director Pete Nickolenko shortly after the latest cancellation, just minutes prior to the scheduled launch. -- AFP