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Two astronauts embarked on a spacewalk outside the International Space Station (ISS) today to complete an upgrade to the station's power supply. The spacewalkers breezed through all their objectives in about half of the allotted time before knocking out a list of optional "get-ahead" tasks.

NASA astronaut and space station commander Shane Kimbrough set out with French astronaut Thomas Pesquet of the European Space Agency this morning (Jan. 13) at 6:22 a.m. EST (1122 GMT), nearly 40 minutes ahead of schedule. The spacewalk was slated to last about 6.5 hours, but as the team breezed through their primary tasks, they constantly progressed farther ahead of schedule, finishing their objectives in just 3.5 hours. [Spacewalk Photos: International Space Station Gets a Power Upgrade]

From the speed and efficiency of his work today, it was hard to tell that this was Pesquet's first spacewalk. Kimbrough, who performed another spacewalk last Friday with NASA astronaut Peggy Whitson last week, completed the fourth spacewalk of his career today.

Today's mission was the second and final spacewalk for the space station's power upgrade process, which began with robotic work in December. In both spacewalks, astronauts worked to replace nine old nickel-hydrogen batteries with six new lithium-ion batteries. Before the spacewalks, a Canadian robotic arm called "Dextre" relocated the new batteries from the HTV-6 cargo spacecraft that arrived in December and placed them into their slots in the Integrated Electronics Assembly (IEA), where the astronauts could then connect them to the power grid. The robotic work saved the spacewalkers the work of lugging all of the batteries around themselves, which means less time spent on the spacewalks. 

The spacewalkers were tasked with installing the new batteries by wiring up electrical connections with special adapter plates. Last week, Kimbrough and Whitson installed three of the six adapter plates and hooked up electrical connections for three of the six batteries. Today Kimbrough and Pesquet completed the installation of the last three batteries and adapter plates.

Dextre will now complete the whole power upgrade process by moving nine of the old nickel-hydrogen batteries onto the HTV-6 cargo craft for storage. When HTV-6 departs the ISS, it will burn up in Earth's atmosphere along with the old batteries. Three of the old batteries will remain stowed at the IEA. Dan Huot, a NASA public affairs officer and NASA TV commentator for today's spacewalk, called the process "a real choreography between robotics and humans."

With the new power upgrade, the lithium-ion batteries will perform more efficiently than the old batteries and can hold more charge. The space station's solar panels charge the batteries, and the astronauts depend on that battery power to maintain power when the ISS passes around the nighttime side of the globe, where sunlight doesn't reach the solar panels.

With three hours to spare after completing the installation of the batteries and adapter plates, Kimbrough and Pesquet had plenty of time to knock out some optional "get-ahead" tasks to help prepare for future operations aboard the ISS. Spacewalks are “fairly labor intensive, so it's very important to pack in as many activities in as short a time as possible,” Huot said. Working with remarkable speed, Kimbrough and Pesquet managed to knock out the entire list of these optional tasks with time left to spare.

The duo made a pit stop at the Quest airlock from which they emerged this morning to drop off some tools and pick up padded shields, which they then carried to the Node 3 or "Tranquility" module. Located at this module are six berthing locations where visiting spacecraft can dock to the ISS. The shields will protect one of Tranquility's pressurized mating adapters from potentially hazardous collisions with space debris.

Kimbrough and Pesquet separated to perform two other get-ahead tasks. Pesquet visited a part of the ISS known as the "rat's nest" to take photos of a jumble of cables for flight planners on the ground, who will use the photos to plan for future spacewalks. Meanwhile, Kimbrough headed to the U.S. Destiny Laboratory to remove two unnecessary handrails, making room for two communication antennas that will be installed in future spacewalks.

After completing "a litany of get-ahead tasks taking them all over the station," as Huot put it, Pesquet led the way back to the Quest airlock, where Whitson and Russian cosmonaut Oleg Navitskiy helped them back inside the station and out of their spacesuits. The spacewalk ended at 12:20 p.m. EST (1720 GMT) after five hours and 58 minutes.

Kimbrough has now racked up a total of 25 hours and 22 minutes of spacewalk time in his career. Pesquet, a rookie astronaut at the ISS, now holds five hours and 58 minutes of total spacewalk time. It may have been his first spacewalk, but he made it look like a piece of cake!

Email Hanneke Weitering at hweitering@space.com or follow her @hannekescience. Follow us @Spacedotcom, Facebook and Google+. Original article on Space.com.