CAPE CANAVERAL, Fla. - Endeavour's astronauts accomplished the No. 1 objective of their mission Thursday, installing a $2 billion cosmic-ray detector on the International Space Station to scan the invisible universe for years to come.

But hours after astronauts finished that work, NASA said it might add one more job: a detailed inspection this weekend of a troublesome damaged thermal tile on the space shuttle's belly.

The space fliers used a pair of robot arms to remove the Alpha Magnetic Spectrometer from the shuttle, then hoist it onto the sprawling framework on the right side of the station. It marked the grand finale for America's role in the construction of the orbiting outpost, which began 13 years ago.

The instrument - which has a 3-foot magnet ring at its core - is the most expensive piece of equipment at the space station and the most prominent scientific device. It will search for antimatter and dark matter for the rest of the life of the station, and hopefully help explain how the cosmos originated.

Nobel laureate Samuel Ting, the principal investigator, personally relayed his thanks from Mission Control in Houston. He's worked on the project for 17 years and fought to get it on a shuttle, when its flight was suspended several years ago.

"This has been a very difficult experiment, and I think in the next 20 to 30 years, nobody will be able to do such a thing again," Ting told the astronauts. "I hope together with you, we will try to make a contribution to a better understanding of our universe."

Shuttle commander Mark Kelly - whose wife, Rep. Gabrielle Giffords, had surgery to repair her skull Wednesday - said he held his breath as the spectrometer was latched down.

He took into orbit his wife's wedding ring; he's wearing it on a chain around his neck. He also has the turquoise wristband he's worn for months - bearing the name "Gabby," a peace symbol, and a heart. Some of the 11 other orbiting astronauts are wearing similar bracelets.

NASA engineers spent Thursday analyzing damage to seven spots on the shuttle's belly where thermal tiles were gouged and nicked during Monday's liftoff, the second-to-last for the shuttle program. They determined that five, and probably a sixth, were no problem. But they weren't sure about one last one.

They have planned an unusual closer inspection Saturday of the gouge, which is about the size of a deck of cards. The shuttle astronauts would use a camera and a laser attached to a giant boom to examine the suspect tiles, deputy shuttle program manager LeRoy Cain said.

Giffords' Surgery Goes Well

Rep. Gabrielle Giffords (D., Ariz.) is making good

progress following skull surgery to replace bone removed after she was shot in the head in January, surgeons at Memorial Hermann-Texas Medical Center

in Houston said Thursday.

During the 31/2-hour procedure Wednesday, surgeons also implanted a shunt to drain away any fluid that might accumulate in the skull and cause pressure on the brain, said Dong Kim, chair of neurosurgery.

A section of Giffords' skull was removed after the Jan. 8 shooting to allow the brain to swell without it being squeezed in a confined space.

Giffords "is recovering very nicely. Her cognition has improved significantly, and we are having more meaningful and fun conversations," said Gerard Francisco, chief medical officer of Memorial Hermann.

Giffords had been wearing a helmet to protect her brain in case she fell during rehabilitation, but she will no longer have to wear it, doctors said.

Her head is still swathed in bandages, but Francisco said: "I have already started calling her Gorgeous Gabby. She hasn't looked in a mirror yet, but as soon as she does, she'll be pleased."

- Los Angeles Times