By Irene Klotz

CAPE CANAVERAL, Fla., June 19 (Reuters) - Space shuttle Atlantis prepared to depart the International Space Station on Tuesday, leaving behind new solar wings to boost power, a fresh crew member and a mystery about what knocked out the outpost's computers.

Commander Frederick Sturckow and pilot Lee Archambault are scheduled to ease Atlantis out from its berthing port at 10:42 a.m. EDT (1442 GMT). Archambault will then steer the shuttle completely around the station while his crewmates videotape and photograph their work on the complex.

"It's very exciting to see the station in this configuration," space station flight director Holly Ridings said.

The pair of new solar wings should provide enough electricity for the installation of laboratories built by Europe and Japan, which are partners in the 16-nation, $100 billion project.

The U.S. space agency had a rough start to its first flight of the year, with launch delayed three months so Atlantis' fuel tank could be repaired after a battering hail storm. Liftoff on June 8 was flawless, but troubles began shortly after Atlantis reached orbit.

During an initial sweep of the shuttle's heat shield to check for damage from launch, engineers spotted a piece of thermal insulation that had torn loose from an engine pod at the back of the shuttle.

The agency began an around-the-clock effort to determine if the shuttle's condition was safe for atmospheric re-entry. The question has been in the forefront since the shuttle Columbia was destroyed, killing seven astronauts, in 2003 due to structural damage caused by an impact with debris during liftoff.

Then, while spacewalking astronauts James Reilly and John "Danny" Olivas installed a massive metal beam containing the station's third pair of solar power panels, a trio of critical computers that control the station's steering crashed, temporarily raising concerns that the outpost would have to be abandoned.

NASA added two days and a fourth spacewalk to the planned 11-day mission so the astronauts would have time to tuck the protruding thermal blanket back down. The extra days were needed to give engineers time to resuscitate the failed computer network.

The shuttle took over the job of positioning the outpost while the station's rocket-powered steering system was disabled.

After skipping two nights' sleep, station commander Fyodor Yurchikhin and flight engineer Oleg Kotov rigged the computers so that suspect circuits were bypassed.

"We essentially bypassed the problem," said Phil Engelauf, a NASA mission manager. "I wouldn't say we fixed it."

The best guess as what caused the crash appears to be some subtle shift in the electrically charged plasma that the station flies through as it orbits 220 miles (350 km) above Earth. The theory is that change occurred as the station's shape and mass expanded with the addition of the 17-ton truss segments.

Atlantis is scheduled to land at the Kennedy Space Center in Florida at 1:54 p.m. EDT (1754 GMT) on Thursday.

AlertNet news is provided by