Shuttle Endeavour astronauts scrambled aboard their spaceship today for a sixth attempt to begin a 16-day mission to the International Space Station and fit it with the last piece of Japan's research laboratory.
After two delays this week due to bad weather and a trio of earlier postponements from fuel leaks and lightning strikes, Nasa was hopeful rain and thunderstorms enveloping the Kennedy Space Center would clear out in time for a 6.03pm EDT (2203 GMT) liftoff of Endeavour.
Meteorologists said there was a 60 per cent chance that conditions would be suitable for launch.
Nasa has just Wednesday and Thursday for this week's remaining launch attempts before managers at the US space agency would reschedule the flight for late July to allow time for a Russian Progress resupply ship to launch and dock at the station.
The six-man, one-woman Endeavour crew, led by two-time shuttle veteran Mark Polansky, headed to the launch pad and began boarding the ship about 2.30pm EDT (1830 GMT).
Endeavour's cargo includes a platform for experiments, the final segment of Japan's elaborate three-part Kibo laboratory. The first two segments were ferried to the station by shuttle crews last year. The platform can hold experiments that need to be exposed to the open space environment.
The $2.4 billion Kibo complex includes a robotic crane and a small airlock to retrieve and replace experiments on the platform without the need for time-consuming and risky spacewalks by the station crew.
The platform is to be installed during the first of five spacewalks planned during Endeavour's 11-day stay at the station. The spaceship's visit to the orbital outpost was shortened a day after Endeavour's last launch delay on Monday.
NASA skipped a launch attempt on Tuesday to replace covers on the shuttle's steering thrusters, needed to prevent rain from seeping inside the jets while the shuttle sits at the launch pad. The jets are needed to maneuver the orbiter once it is in space.
The crew includes rookie astronaut Timothy Kopra, who will be staying aboard the station to take over the flight engineer's job held by Japan's Koichi Wakata.
Wakata, who has been aboard the outpost since March, will be returning home with the rest of the Endeavour crew on July 29th.
Nasa has eight missions remaining to complete construction of the station, a $100 billion project of 16 nations. The station orbits 220 miles (354 km) above Earth and has been permanently occupied for nearly nine years.
Reuters