Canadian astronaut Steve MacLean and his five crewmates put on their orange space suits Friday morning as they prepared for the launch of space shuttle Atlantis in Florida.

NASA crews fueled the spacecraft early Friday in anticipation of the much delayed launch at 11:40 a.m. and they were forced to attend to a fuel sensor problem as preparations got underway.

The U.S. space agency has decided to proceed with the mission despite the problem with one of the power cells.

MacLean and his crewmates took a NASA bus to the launch pad on Friday. It has been 14 years since MacLean was last in space.

The fuel sensor problem is different from an earlier problem that emerged this week with an electricity generating fuel cell.

Crews pumped more than 19,000 litres of liquid hydrogen and liquid oxygen into the shuttle before 3 a.m. Friday. The fueling took place more than a hour later than planned because crews had to replace a nitrogen valve on the launch pad.

Early wake-up call for astronauts

As crews prepared the shuttle for launch, the astronauts themselves prepared for blastoff. They were reportedly out of bed before 1 a.m. ET to get ready. They are expected to take an enormous solar array to the international space station to boost its power capacity.

Atlantis was originally set to launch on Aug. 27 but was delayed when lightning struck the space centre two days before. The launch was rescheduled, but had to be postponed again because of the approach of tropical storm Ernesto. It was delayed early Wednesday when the fuel cell problem arose.

MacLean and five other astronauts have been preparing for more than four years to go into space to perform construction work on the international space station during a mission that is expected to last 11 days.

NASA said the weather forecast looks promising for Friday and it said there is a 70 per cent chance that it will be clear.