CAPE CANAVERAL (AP) - 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.
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 certainly 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.
"It's a $2 billion cosmic particle detector, it's got 600 physicists that have been working on it ... and it was all in the hands of four of my crew members," Kelly said in an interview with The Associated Press. He said he told his crew afterward, "Isn't it a relief that it's no longer our responsibility, that we safely got it installed?"
As for his wife, Kelly said she's doing "really, really well, as good as possibly could be expected" following Wednesday's surgery in Houston, just two days after seeing her husband blast into orbit. Doctors put in a piece of mold plastic to replace part of her skull that was removed after she was wounded in the head in a Jan. 8 shooting rampage in Tucson, Ariz., that left six dead and 13 injured.
Kelly said he hoped to call Giffords later Thursday, using the space station's Internet phone. He spoke with his mother-in-law and identical twin astronaut brother Scott on Wednesday, and exchanged e-mails with his wife's neurosurgeon and chief of staff.
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.
Back at Mission Control, meanwhile, engineers continued to analyze several areas of damage on Endeavour's belly. Thermal tiles were gouged and nicked during Monday's liftoff, the second-to-last for the shuttle program. Some of the slashes are as much as 6 inches long and 2 inches wide.
NASA wants to make certain the shuttle is safe to come home in two weeks.
The damage was spotted in photos snapped by the space station crew just before Endeavour docked Wednesday. The shuttle performed a slow backflip for the cameras, a customary procedure put in place after shuttle Columbia disintegrated as it re-entered Earth's atmosphere in 2003.
Mission Control may ask Kelly and his five crewmates to take a closer look at the gouges this weekend, using a laser-tipped inspection boom. Kelly said he's being kept abreast of the developments and is not particularly concerned.
"From my point of view, the pictures I've seen, we've seen this kind of thing before," Kelly told the AP. On his 2006 shuttle flight, similar damage was detected and later cleared for re-entry, he said.
The 7-ton Alpha Magnetic Spectrometer, better known by its acronym AMS, may well vindicate the scientific purpose of the space station, according to astronauts, researchers and others.
"A science voyage of discovery into our galaxy and beyond has started today from the International Space Station," said Mark Sistilli, who's served as NASA's program manager for the spectrometer since 1994.
The international team of 600 scientists is led by Ting, a physicist at the Massachusetts Institute of Technology.
Weary after being up all night, Ting said Thursday afternoon that the spectrometer was turned on and gathering data within a couple hours of being installed, with thousands of particles passing through the magnet. Everything seems to be working perfectly, he said, but the checkout will continue for another few days before data collection begins in earnest.
The magnetic field generated by the precision instrument bends the path of incoming cosmic particles, and eight detectors attempt to identify them in the nanoseconds it takes to travel through the magnet.
Two astronauts - Gregory Chamitoff and Andrew Feustel - will venture out Friday on the first of four spacewalks to perform some station maintenance. On Saturday, the two crews will get an unprecedented VIP call - Pope Benedict XVI will make the first papal call to space. Two Italians are on board.
Endeavour will conclude its final voyage with a landing on June 1. NASA is shutting down its shuttle program this summer after 30 years, to focus on interplanetary travel. One more mission remains, by shuttle Atlantis in July, to carry up one last load of supplies and equipment.
Alpha Magnetic Spectrometer: www.ams02.org/