Dec. 2 (UPI) -- NASA astronaut Andrew Morgan and European Space Agency astronaut Luca Parmitano are back in the International Space Station after completing the third in a series of complex spacewalks aimed at fixing an experimental physics device designed to detect antimatter in cosmic rays.
During the first few hours outside ISS, Morgan and Parmitano "completed all primary tasks for today's spacewalk and started work on get ahead tasks," according to a Twitter update from the International Space Station.
The duo switched their spacesuits to battery power -- the official beginning to all spacewalks -- at 6:31 a.m. ET on Monday morning. Though they were originally scheduled to spend 7.5 hours outside the space station, Morgan and Parmitano finished their work early, returning to ISS at 12:33 p.m. ET -- a six-hour-and-two-minute spacewalk.
The mission was broadcast live on NASA TV.
"The two astronauts successfully installed a new cooling system for the Alpha Magnetic Spectrometer," ISS wrote on Twitter.
The Alpha Magnetic Spectrometer was installed in 2011. Over the last few years, the instrument has observed hundreds of thousands of positrons, the antimatter counterpart of the electron. Data collected by the AMS could help scientists determine the mysterious makeup of dark matter, which accounts for most of the mass in the universe.
But the device wasn't designed to last this long, nor be serviced in space. To fix the instrument's broken cooling pumps, engineers had to develop special tools and send them to the space station.
In addition to prolonging the AMS experiment, the series of complex spacewalk missions has helped NASA astronauts gain valuable troubleshooting experience.
"The process of creating the tools and procedures for these spacewalks is preparing teams for the types of spacewalks that may be required on Moon and Mars missions," NASA wrote. "The tools include plumbing instruments to cut into the cooling lines, new screwdriver bits and devices to capture the fasteners the astronauts remove from AMS."
In addition to successfully repairing the AMS's cooling system, the two spacewalkers also completed several get-ahead tasks.
"The astronauts also completed an additional task to install an insulating blanket on the nadir side of the AMS to replace the heat shield and blanket they removed during the first spacewalk to begin the repair work," NASA wrote in an update. "The flight control team on Earth initiated power-up of the system and confirmed it is receiving power and data."