LLULLAILLACO VOLCANO, Chile -- U.S. adventurer Steve Fossett was forced to strap on his parachute on Thursday for a roller-coaster ride over the towering Andes as he passed the halfway point in his bid to become the first solo balloonist to circle the world, Reuters reported.

Repeatedly dropping, then soaring, hundreds of feet amid fierce turbulence as he cleared South America's backbone, Fossett weathered a passage that brought back harrowing memories of a 29,000-foot (8,845-meter) plunge that nearly killed him on his last solo attempt, his support team said.

After crossing from Chile into northern Argentina, the 57-year-old millionaire descended to around 20,000 feet (6,100 meters) to help conserve dwindling oxygen supplies and catch some sleep before heading out across the Atlantic.

"He had a pretty good shaking," said Jim Mitchell, a member of Fossett's mission control team in St. Louis. "The wind was shifting around and bouncing him up and down, and he said he put on his parachute as a precaution."

"He remembers that 29,000-foot drop in the Coral Sea," Mitchell added, referring to Fossett's solo round-the-world bid in 1998, when fierce thunderstorms ripped his canopy and left him bobbing, bruised and battered, in the ocean.

Crescent Moon, Lone Star

Before hitting the rough spot, Fossett's balloon had cruised by the 22,000-foot (6,720-meter) Llullaillaco Volcano on Chile's border with Argentina under a crescent moon and a lone star.

Argentine air traffic authorities turned back a Piper Navajo light plane carrying Reuters journalists following Fossett into Argentine air space to film and photograph the towering, silver-colored balloon over the mountains at dawn.

Fossett was heading for the city of Resistencia in northern Argentina and was due to drift over the southern tip of Brazil before heading out across the Atlantic on Friday morning. The ocean crossing was expected to take four days.

Having safely crossed the Andes, Fossett -- whose capsule has no windows except for a plastic bubble hatch on top -- now faces thunderstorms across northern Argentina. But he was expected to fly above them.

The expedition's web site, at www.solospirit.wustl.edu, said Fossett had slowed to 34 mph (55 kph) pace. He began his latest bid to become the first person to circumnavigate the globe alone in a balloon from western Australia on Aug. 4.

His slower than expected crossing of the vast Pacific Ocean means that original forecasts of a two-week flight are out of reach. The trip will take at least 17 days and perhaps up to 20.

Fossett has water for only another 15 days.