'Discovery' takes the slow piggy-back home

It left Edwards Air Force Base, about two hours north of Los Angeles, shortly after eight in the morning yesterday and due was to arrive in Florida last night.

For aviation enthusiasts the shackling of a shuttle to the spine of a jumbo jet creates one of the more exotic sights in the sky. It happens whenever weather conditions prevent a returning shuttle from landing on its usual Florida airstrip.

Discovery was delayed a day in coming back to Earth after its recent 14-day mission because of thunderstorms over Florida. It finally landed in California on 9 August. Since then engineers have been ridding it of all hazardous materials, including fuel, before mounting it on the Boeing.

For a craft designed to zip through space, the ride to Florida is cumbersome. The pilots of the 747 were due to make several pit-stops along the way, the first in Oklahoma, just to refuel because of Discovery's weight and its air resistance.Engineers had also fitted an extra cone to the tail of Discovery to reduce the drag in the air.

The return of the shuttle two weeks ago brought relief for Nasa, after Columbia disintegrated above Texas during its return to Earth two and a half years ago. Any celebration was tempered, however, by continuing safety concerns and the announcement last week that the agency does not expect to launch any more shuttle missions until next year.