The Saturn V rocket lifts off from pad 39A. Photo: NASA/KSC

Apollo 13 and its three-man crew have been successfully launched into Earth orbit, and are now being checked out before being placed in a 75-hour trajectory to the moon -- longer than usual because the moon is almost at its maximum distance of 252,000 miles.

As usual the unexpected happened just after a perfect lift-off. The 3,250-ton vehicle roared into a hazy sky, but with none of the heavy cloud forecast to obscure the view of the dazzling, golden flame from rockets producing 7.6 million pounds of thrust.

But satisfaction in Launch Control turned to dismay when the centre engine on the second stage cut off two minutes early -- a long time in rocketry. The onboard computers immediately ordered the other four engines to burn 30 seconds longer. Then the third stage S4B also had to fire an extra 30 seconds to bring the spacecraft's speed up to the required 17,500 mph to get it into earth orbit.

Anxiety then that there wouldn't be enough fuel left for the 6-minute burn needed later to launch Apollo 13 out of earth orbit at 24,000 mph into its lunar trajectory. Hasty calculations showed that there was sufficient margin.

Jim Lovell, accustomed to such situations after over 500 hours in space, commented: "It's good to be up here again". Swigert, well aware that Ken Mattingly, whose place he had taken, was listening in Mission Control, said little. As they disappeared from sight, Mattingly knew that at best he'd get another chance at the end of the year.

Apollo 13's lunar module, Aquarius, isn't due to touch down on the moon, in the rugged Fra Mauro area -- named after a 15th century astronomer monk -- until 3.55 am British time next Thursday. But one of the most exciting events of the whole mission comes in the early hours of Wednesday, when the 15-ton third stage rocket will be crashed into the moon at nearly 6000 mph -- with dramatic effects on the seismometer left on the moon by Apollo 12.