The space shuttle Discovery arrived home atop a jumbo jet Saturday, five days after completing America's first manned space mission since the Challenger tragedy.

A Boeing 747, with the shuttle bolted on its back, descended through a cloud deck and glided to a runway touchdown at 7:04 p.m. EDT as darkness descended on the Kennedy Space Center. The return flight began Saturday morning at Edwards Air Force Base, Calif.Because the Kennedy runway is not heavily lighted and because of cloudy weather, NASA officials were considering diverting the shuttle aircraft to Eglin Air Force Base in Northwest Florida for an overnight stay.

But half an hour before landing, an advance plane reported conditions favorable, and the jumbo jet came on in.

Thousands of spectators turned out to applaud the return, lining roads and river banks and creating huge traffic jams at the space center. Most of them were among the hundreds of thousands who were here to cheer Discovery's departure on Sept. 29.

Technicians planned to remove the shuttle from its carrier plane overnight and tomorrow, and then tow it to a processing facility to prepare it for its next flight. Officials reported it returned from space in such good shape that little refurbishment work will be needed.

Discovery and its five-man crew landed on the hard clay Rogers Dry Lake bed at Edwards last Monday, four days after its launch from Cape Canaveral, Fla. More than 400,000 people came to cheer the returning astronauts.