Commander Shane Kimbrough and French crew member Thomas Pesquet plugged in three new lithium-ion batteries, adding to the three hooked up last week.
Just like before, the station's robotic handyman saved the spacewalkers considerable time — and risk — by removing the decade-old nickel-hydrogen batteries and positioning the new ones for wiring. The robot is named Dextre, short for dexterous, with 11-foot-long arms that were operated remotely by flight controllers in Houston.
Kimbrough and Pesquet hustled through the job. Within three hours, the men successfully wrapped up the battery work.
Pesquet, a rookie astronaut, became France's first spacewalker in 15 years. He called it "a big day."
"Better bring our A-game," Pesquet said in a tweet Thursday evening, "to be safe & efficient."
NASA describes the lithium-ion batteries as critical upgrades to the space station's solar power system. Eighteen more need to be installed over the next two to three years, for a total of 24. The next batch will arrive late this year or early next.
The batteries store electrical power generated by the massive solar wings and are used to run equipment when the 250-mile-high lab is on the nighttime side of Earth.
Both the new and old batteries are the same size: about 3 feet long and wide, and 1 ½ feet tall, or about as big as half a refrigerator. But the new lithium-ion batteries can hold more charge and keep it longer, and so only half as many are needed — 24 instead of 48.
Nine of these old batteries will be trashed at the beginning of February, burning up in the atmosphere along with the trash-filled Japanese cargo ship that delivered them last month.
For the Jan. 6 spacewalk, Kimbrough paired up with the other American on board, Peggy Whitson, the world's oldest and most experienced spacewoman. The lab is also home for three Russians.
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.
Spacewalk 2017 Astronauts Shane Kimbrough, Thomas Pesquet Upgrade ISS Power System
Kimbrough and Pesquet's tasks for Friday's spacewalk centered around installing adapter plates and connecting three lithium-ion batteries on the starboard truss, according to a NASA blog post. Kimbrough and flight engineer Peggy Whitson put another three batteries in place Jan. 6. When everything is finished, the astronauts will put the old nickel-hydrogen power sources on an external pallet for disposal.
On its website, NASA describes spacewalks as "any time an astronaut gets out of a vehicle in space," either to conduct experiments, do repairs or test equipment. As such, spacewalks occur periodically at the ISS — since 1998, there have been 196 spacewalks there. The distribution varies: in 2007, for example, astronauts conducted 20 spacewalks, but last year they only carried out three.
Outside the ISS, conditions are harsh. Flight engineer Doug Wheelock tweeted Friday that astronauts experienced temperatures of about 275 degrees Fahrenheit in sunlight and -275 degrees in shadow. When he went on his first spacewalk, Wheelock said, he "experienced a range of intense feelings ... from euphoria floating weightless to fear of the unforgiving environment."
The ISS, the first piece of which launched in 1998, is 356 feet long and weighs nearly 1 million pounds. It sees up to 10 people at a time.