Their salvage mission over, the five astronauts aboard the space shuttle Discovery today prepared to return to Earth Friday at Florida's Kennedy Space Center.

Weather permitting, the crew will land the 100-ton spaceliner -- with its cargo of two $35 million satellites -- at 6:54 a.m. EST, just a few minutes after sunrise.

The weather forecast was excellent, with a prediction of light winds, no rain and only a slight chance of patchy ground fog.

Today flight directors discussed with the crew the precautions they will have to take during reentry and after the shuttle lands.

The satellites still could contain as much as 400 pounds of toxic hydrazine fuel that was never burned during their eight months in space. If this fuel gets too hot during reentry it could ignite; if it gets too cold after the shuttle's cargo-bay doors are closed, it could freeze, expand and break open the fuel tanks.

If the fuel freezes, the crew might be forced to make another spacewalk and leave the satellites in space.

"This is the only answer to this worst-case scenario," a spokesman at the Johnson Space Center said.

"We don't think there will be any hydrazine leakage on Friday when we come home," Flight Director Randy Stone said. "Those fuel tanks in the satellites have triple linings to keep the fuel inside, and that's the best that we can do."