Clouds of concern gathered for tonight’s lift-off of the US space shuttle Discovery as Nasa downgraded launch chances to 40% due to weather.

Even though Tropical Storm Ernesto and a lightning strike postponed the lift off of the space shuttle, the delay of a week may give NASA managers good weather for launching Atlantis, officials said today.

Atlantis’ six astronauts arrived at Kennedy Space Centre today as the countdown clock began ticking toward a Sunday launch of the space shuttle.

The delivery of a German astronaut to the international space station and the scheduled spacewalk of a British astronaut were put in doubt today as a cloudy weather forecast may delay this weekend’s launch of the space shuttle Discovery.