Crowds Scramble for Shuttle's Return to Space

Nasa's long-awaited return to manned spaceflight looked in jeopardy last night after technicians accidentally chipped part of the space shuttle Discovery less than 24 hours before today's scheduled liftoff.

The space agency worked frantically overnight to assess the damage. It announced early this morning it had made the necessary repairs and the launch would go ahead, weather permitting.

Engineers who had been making final preparations appeared to have dropped a window cover from its position close to the crew cabin, sending it crashing 15 metres (50ft) down the launchpad and on to the shuttle's left-side orbital manoeuvring system.

The news came as a blow to the space agency's hopes of re-establishing its reputation two and a half years after the shuttle fleet was grounded following the Columbia disaster, which killed seven astronauts.

Nasa said Discovery was still on track to take off today. But there were doubts about how many knock-on safety problems the accident might have caused.

More than 100 safety improvements have been made to the shuttle fleet since Columbia blew up on re-entry over Texas. They include a complete redesign of the external fuel tank and extra-strength windows to minimise the risk of impact from space debris.

Half a million spectators were expected to make their way to Cape Canaveral for today's launch. Such massive interest was last seen in September 1988 when Discovery put Americans back in space after the January 1986 Challenger disaster, in which seven astronauts also died.

A Gallup poll during the run-up to today's launch indicated that 77% of Americans support Nasa's plans to complete the construction of the international space station before the ageing shuttle fleet is retired in 2010, and to develop a replacement spacecraft able to project humans beyond Earth's lower orbit for the first time.

The study also showed that, despite a national debt of $7.85 trillion, 73% of adults in the US believe that the government is right to give 0.7% of the federal budget, or $58 (£33) for every US citizen, to Nasa each year.

The Nasa team was also watching the weather last night,with the space agency acknowledging that thunderstorms, including the formation of tropical storm Emily in the eastern Caribbean, coulddelay the launch.

"For our launch forecast, we did get a little more pessimistic on this today," said Kathy Winters, the shuttle's weather officer.

Today's liftoff is scheduled for 3.51pm local time (8.51pm BST).

If no launch is possible, mission controllers could launch tomorrow afternoon or Friday.

But if they fail to launch by July 31 the entire 12-day mission will be put back until September.

Wayne Hale, the deputy manager of the space shuttle programme, said that was the worst-case scenario.