NASA said its systems were in good shape and the countdown was going well for the launch of the Space Shuttle Discovery's mission to the International Space Station.
Set for tomorrow at 0805 IST, it will be the first night launch since the Columbia disaster in 2003 as NASA races to finish building the ISS by 2010.
"Our systems are currently in great shape, countdown is progressing and we have no issues of consequence," Steven Payne, test director of the National Aeronautics and Space Administration (NASA), told a media briefing.
"The teams are ready and we are looking forward to an incredible mission (for the) space shuttle Discovery and a safe and successful landing," he said.
The countdown for the launch began at the Kennedy Space Centre in Cape Canaveral, Florida at 0930 IST on Tuesday.
No major meteorological problems are foreseen for the 10-minute launch window, with only a 30 per cent chance of weather scuttling liftoff tomorrow, it added.
However, should there be a 24-hour or 48-hour delay, then the weather risk would increase to 60 per cent.
"So, overall, the first day is the best day weather-wise," said Kathy Winters, the shuttle weather officer. Strong winds cause a "lot of concern" with a 24-hour and 48-hour delay, she said.
NASA officials say Discovery's 12-day mission to rewire the orbiting ISS in two spacewalks is its most complex to date. The astronauts will also bring an 11-million-dollar truss segment to be added to the orbiting laboratory in a third walk.