Astronauts upgrade station power system in six-hour spacewalk

Two astronauts floated outside the International Space Station on Friday for a six-hour spacewalk to replace aging batteries for the laboratory's solar power system, an upgrade needed to keep the outpost running into the next decade, NASA said.

U.S. astronaut Shane Kimbrough left the station’s airlock at about 6:30 a.m. EST (1130 GMT) to begin his second spacewalk this month. He was joined minutes later by French crew mate Thomas Pesquet, a rookie astronaut making his first spacewalk.

Kimbrough and Pesquet breezed through work on the batteries and completed several maintenance chores before heading back inside the station just before 12:30 p.m. EST (1730 GMT), a half-hour earlier than originally planned.

"Thanks for all the help,” Kimbrough radioed to NASA’s Mission Control in Houston.

The men continued work started during a spacewalk earlier this month to hook up an array of 428-pound (194 kg) lithium-ion battery packs, about the size of a small refrigerator, to the station's solar power system. They replace nickel-hydrogen batteries that are losing the ability to hold a charge.

The first six of the new 24 lithium-ion batteries arrived at the station aboard a Japanese HTV cargo ship in December. The remaining 18 new lithium-ion battery packs will be flown to the station on future Japanese resupply missions.

Nine of the old batteries will be loaded aboard the cargo ship that will depart the station later this month and burn up in the atmosphere. Three defunct batteries will be stored outside the station.

The U.S. National Aeronautics and Space Administration expects it will take about three years to complete the space station's power system upgrade, which will keep it operational until at least 2024.

Before this month's spacewalks, ground control teams used the station's robotic arm to move the new batteries into position and remove the old ones. This robotics work cut the number of spacewalks needed for the project from six to two, NASA said.

The solar-powered station draws power from the batteries when it flies in darkness, circling about 250 miles (400 km) above Earth.

The space station, which is about the size of a five-bedroom house, is a $100 billion research laboratory, owned and operated by 16 nations.

(Editing by Letitia Stein and Bill Trott)