CAPE CANAVERAL, Fla. (AP) -- Astronauts began an extraordinarily complicated series of spacewalks Friday to fix a cosmic ray detector at the International Space Station.
Italian astronaut Luca Parmitano and U.S. astronaut Andrew Morgan ventured out Friday with dozens of tools to dissect the Alpha Magnetic Spectrometer. NASA considers these spacewalks the most difficult since the Hubble Space Telescope repairs a few decades ago.
Unlike Hubble, the spectrometer was never meant to undergo space surgery. After 8 years in orbit, its cooling system is almost dead.
Parmitano and Morgan will go out at least four times this month and next to revitalize the instrument. NASA describes the work as a heart bypass.
Delivered to orbit by Endeavour in 2011 on the next-to-last space shuttle flight, the $2 billion spectrometer is hunting for elusive antimatter and dark matter.
It's already studied more than 148 billion charged cosmic rays. That's more than what was collected in over a century by high-altitude balloons and small satellites, said lead scientist Samuel Ting, a Nobel laureate at the Massachusetts Institute of Technology. He monitored Friday's spacewalk from Mission Control in Houston.
The huge spectrometer --- 16 feet by 13 feet by 10 feet (5 meters by 4 meters by 3 meters), with a mass of 7 tons (6,800 kilograms) --- was designed to operate for three years. By installing four new and improved coolant pumps, the astronauts can keep it working throughout the life of the space station, or another five to 10 years. The replacement pumps arrived at the space station nearly two weeks ago, along with an assortment of new tools.
Parmitano, the lead spacewalker, and Morgan trained extensively for the plumbing job before rocketing into orbit. Friday's task entailed removing a debris shield to gain access to the inside of the spectrometer and tossing it overboard. The next spacewalk on Nov. 22 will involve slicing through stainless steel tubes and splicing in connections for the new pumps, which like the old will use liquid carbon dioxide as the coolant.
In some respects, this work, 250 miles (400 kilometers) up, is even trickier than the Hubble spacewalks, said NASA project manager Ken Bollweg. As before, the stakes are high.
"Any time you do heart surgery you're taking some risks," Bollweg said in an interview earlier this week. Ting added that he was not anxious and had full confidence in the spacewalkers.
Morgan is an emergency physician in the Army --- a bonus for this kind of intricate work. He's making his first spaceflight.
"Heck of a sunrise there," Morgan told Parmitano as they made their way to the spectrometer, urging him to get photos.
For second-time station resident Parmitano, it marked his return to spacewalking following a close call in 2013. He almost drowned when his helmet flooded with water from the cooling system of his spacesuit. Unable to talk because of the rising water, he managed to keep his cool as he made his way back to the safe confines of the space station.