Shuttle Atlantis heads back home

Shuttle Atlantis started for home on Tuesday, leaving the International Space Station with new solar power wings, a fresh crew member and a mystery over what knocked out the space station's computers.

Commander Frederick Sturckow and pilot Lee Archambault gently eased Atlantis from its berthing port at 10:42 a.m. EDT (3:42 p.m. British time), then circled the shuttle around the station while the crew took pictures of their work on the complex.

Cameras aboard both spacecraft televised the orbital ballet live, with Atlantis' empty cargo bay and thruster rocket firings visible against a black sky and the station's lanky symmetry restored with the new pair of sparkling wings.

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

Atlantis was scheduled to land at the Kennedy Space Center in Florida at 1:54 p.m. EDT (6:54 p.m. British time) on Thursday.

The best guess as to what caused the computer crash appeared to be some subtle shift in the electrically charged plasma that the station flew through as it orbited 220 miles (350 km) above Earth.

The theory is that the shift occurred as the station's shape and mass expanded with the addition of the 17-ton truss segments that hold the solar wings. The crash temporarily raised concerns the outpost would have to be abandoned.

The U.S. space agency NASA had a rough start to the flight. A hail storm battered Atlantis' fuel tank, delaying the launch three months. A June 8 liftoff was flawless, but troubles began shortly after Atlantis reached orbit.

BYPASSING THE PROBLEM

During an initial sweep of the shuttle's heat shield to check for damage from the 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.

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 proved a blessing for trouble-shooting the computer problems as well, with the shuttle taking 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 solar power panels should provide enough electricity for the installation of laboratories built by Europe and Japan, both partners in the 16-nation, $100 billion (50 billion pound) project.