Veteran Spacewalkers Tackle Final Space Station Battery Swaps

The last of the nickel-hydrogen batteries were removed from the S-6 truss during Thursday’s EVA-67. Photo Credit: NASA

Bob Behnken now sits within the Top Ten list of the world’s most experienced spacewalkers, with Chris Cassidy only a couple of spots behind, following Thursday’s six-hour session of Extravehicular Activity (EVA) outside the International Space Station (ISS). Working an hour ahead of the timeline, the two former astronaut office chiefs worked with calm professionalism to pluck all six aging nickel-hydrogen batteries out of the station’s far-starboard S-6 truss and install three smaller, lighter and more capable lithium-ion batteries in their place. Wrapping up U.S. EVA-67 after exactly six hours, there is now only a single task remaining to complete a three-year-plus campaign of upgrades on the station’s power infrastructure. A new lithium-ion battery on the P-4 truss, which blew a fuse last year, will be replaced on a future spacewalk.

The first lithium-ion batteries were installed back in January 2017. Smaller, lighter and more capable than their nickel-hydrogen predecessors, they should support the station’s power needs for the remainder of its lifetime. Photo Credit: NASA/Twitter/Thomas Pesquet

Efforts to replace a total of 48 nickel-hydrogen batteries in the space station’s four power-generating trusses—12 each in the starboard-side S-4 and S-6 segments and the port-side P-4 and P-6 segments—with 24 lithium-ion units have been ongoing since January 2017. The S-4 work was done first, followed by the P-4 work in March 2019, with both tasks requiring only a pair of EVAs, as their work sites were situated “inboard”, closer to the center of the station. However, the P-6 and S-6 trusses lie further “outboard”, out of easy reach of the 57.7-foot-long (17.6-meter) Canadarm2 robotic arm, which placed added demands on the spacewalkers in getting themselves, their tools and the batteries out to the worksite. As such, the P-6 battery work, conducted between October 2019 and last January, necessitated four EVAs. And the S-6 task is expected to follow a similar pattern, with Cassidy and Behnken having completed one power channel in two spacewalks on 26 June and 1 July and the second channel during today’s EVA-67.

With the completion of EVA-67, Expedition 63 Commander Chris Cassidy (left) and Flight Engineer Bob Behnken have wrapped up the battery replacements on the S-6 truss. Photo Credit: NASA

Preparations for today’s spacewalk spanned several days. Late last week, the astronauts dumped water and purged gas from their suits and ran through step-by-step procedures and participated in a conference with specialists in Mission Control. The Expedition 63 crew awakened early Thursday, breakfasted and headed directly into EVA preparations in the inner “equipment lock” of the Quest airlock. During this period, Behnken and Cassidy participated in standard In-Suit Light Exercise (ISLE), flexing their arms and legs to speed up their metabolic rates to help rid their blood of excess nitrogen.

Activities to suit-up Behnken and Cassidy occurred in the inner “equipment lock” of the station’s Quest airlock. Photo Credit: NASA

Aided by Expedition 63 crewmates Doug Hurley—sporting “Karen + Jack” socks, in honor of his wife and son—and Ivan Vagner, they donned their suits and Simplified Aid for EVA Rescue (SAFER) backpacks, before being moved into the outer “crew lock” just before 6:30 a.m. EDT. Overseeing today’s spacewalk from the Mission Control Center (MCC) at the Johnson Space Center (JSC) in Houston, Texas, was a team led by Flight Director Allison Bolinger, Capcom Josh Kutryk of the Canadian Space Agency (CSA) and Spacewalk Officer Sandra Moore. Already 25 minutes ahead of the timeline, Behnken opened the hatch at 7:10 a.m. EDT, as the station flew high above South America.    

Bob Behnken at work during his previous EVA on 1 July. Photo Credit: NASA

The two men set briskly to work, with Kutryk’s calm guidance in their earpieces, configuring their tools and tethers and performing “buddy checks” of each other’s suits, before heading to their initial work sites. First up for Cassidy was the installation of a high-definition camera, which was soon confirmed to be relaying good data to the ground. He then joined Behnken to kick off the battery work in earnest. Original plans called for the duo to remove five of the six nickel-hydrogen batteries and install all three lithium-ion batteries, but the astronauts worked so adeptly that at one point they were more than 70 miles ahead of the timeline. Discussions in Mission Control about whether to fit the sixth battery removal into EVA-67 were communicated up to the men by Kutryk.

Bob Behnken now sits at No. 8 on the world list of spacewalking supremos. Photo Credit: NASA

He advised them that they were expected to complete the final battery removal and still be back inside Quest within six hours and 30 minutes, well within the seven-hour limit of their suits’ consumables. Behnken and Cassidy pressed Kutryk at one point about how the additional work would impact their “cleanup” time at the end of the EVA. He responded that at least an hour remained before cleanup needed to start, affording them plenty of time and Mission Control’s preference “to jump into it right here”.

The two seasoned spacewalkers did not need to be told twice and, despite an instance of elevated carbon dioxide levels in Cassidy’s suit and a slight increase in his metabolic rate, they pressed on with the sixth and final battery removal. As EVA-67 drew to a close, the station now has 23 of its planned 24-strong set of lithium-ion batteries fully functional. Another battery, installed onto the P-4 truss by Expedition 59 spacewalkers Anne McClain, Nick Hague and Christina Koch during a pair of EVAs in March 2019, later blew a fuse and two of the old nickel-hydrogen batteries were re-installed to take its place. A replacement lithium-ion battery was launched aboard a SpaceX Dragon cargo mission last December and will be installed on a future spacewalk.

Behnken at work at the S-6 work site. Photo Credit: NASA

Returning inside the Quest airlock at 1:10 p.m. EDT—exactly six hours to the very minute since they stepped outside—Behnken and Cassidy can reflect upon a job well done. Although both men now have nine EVAs to their credit, Behnken sits slightly ahead of Cassidy on actual spacewalking hours, with a grand total of 55 hours and 41 minutes. He made three EVAs on each of his two shuttle flights and has done another three in the last three weeks. This places him in eighth place on the list of the world’s most experienced spacewalkers. As for Cassidy, he now sits at No. 12 on the list, having totaled 49 hours and 22 minutes from three spacewalks on his shuttle flight in 2009, another three from his last ISS increment in 2013 and a further three with Behnken.

Next up for these two spacewalking supremos is another EVA on Tuesday, 21 July, planned to run for up to seven hours. It also is expected to mark the 300th U.S. spacewalk since Ed White poked his head out of Gemini IV on 3 June 1965 and then spent 21 minutes tumbling in the void. Following in White’s footsteps have come another 128 U.S. spacewalkers, including 14 American women. Between them, they have walked on the Moon and floated in the ethereal blackness of cislunar space, they have fixed crippled space stations and repaired and upgraded Hubble. And from three men crammed into an airlock for the first and so-far-only EVA to include more than two people to last year’s triumphant all-female EVA, American spacewalkers have done it all.

By the time we reach the 400th U.S. EVA, perhaps it will be back on the surface of the Moon. Or even Mars.   

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