The Space Shuttle Discovery is set to return to the skies this evening, with its lift-off scheduled for 8:51pm, UK time from the Kennedy Space Centre in Florida's Cape Canaveral.

Last week it looked like the launch might be delayed by the approaching Hurricane Dennis, but by the weekend, the outlook was much improved.

There is a lot riding on the launch, as NASA administrator Michael Griffin acknowledged earlier this week. He told reporters that it is "utterly crucial for NASA, for the nation, for our space programme, to fly a safe mission".

The flight will be the first since the loss of Columbia, which broke up on re-entry back in February 2003, killing all those on board. Columbia was damaged by a falling piece of insulation during take-off. This left a hole in its wing leaving the space-plane vulnerable to the heating effects of re-entry.

The families of those killed in the incident have written a letter offering their full support for NASA's plans to return to flight.

NASA says it has done everything it knows to do to improve safety for the launch this evening. The shuttle has been significantly modified, with a new 50ft robotic arm that will look for any damage to the craft once it is in orbit, and heaters on the massive fuel tanks, to prevent large chunk of potentially dangerous ice forming during the countdown procedure. ®

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