Two astronauts floated outside the International Space Station early Friday for the first of four planned spacewalks to wrap up a complex multi-year job to replace 48 aging batteries in the lab's solar power system with 24 more powerful lithium-ion units.
Getting off to a fast start, space stationand ran well ahead of schedule throughout the day, completing all of their planned tasks and starting work originally planned for the next spacewalk in the series next Wednesday.
"I think we've done enough for one day," one of the spacewalkers quipped before heading back to the airlock to wrap up a six-hour seven-minute excursion.
The battery replacement work began in January 2017 and based on Friday's results, the astronauts should be able to complete the work next month, ensuring smooth, reliable power distribution through the rest of the decade if not beyond.
"I think it's safe to say, barring any unforeseen type of failures, we'll be good on batteries for a number of years to come," said Kenny Todd, deputy space station program manager at the Johnson Space Center in Houston. "The longevity of the new technology batteries gets us well out through what will most likely be the end of the program."
Floating in the Quest airlock module, Cassidy and Behnken switched their spacesuits to battery power at 7:32 a.m. EDT to officially kick off the 228th EVA in station history, the fourth so far this year and the seventh for both astronauts.
Assisting with the lab's robot arm from inside the station were Douglas Hurley, Behnken's crewmate aboard theMay 30, and cosmonaut Ivan Vagner, who launched aboard a Soyuz on April 9 with Cassidy and cosmonaut Anatoly Ivanishin.
Floating out of the airlock, Cassidy reported that a small wrist mirror, used to help him read spacesuit displays that cannot be seen directly, had somehow worked loose and drifted away at about a half a mile per hour. Tipping the scales at just a tenth of a pound, the lost mirror posed no threat to the station or the crew, and in any case Cassidy had a spare.
NASA is wrapping up the replacement of all 48 of the space station's older-generation nickel-hydrogen batteries with 24 smaller yet more powerful lithium-ion units, along with circuit-completing "adapter plates" to fill in for batteries that were removed but not replaced.
The new batteries are arranged in sets of six in integrated electronics assemblies, or IEAs, at the bases of the station's four main solar array wings. Each wing is made up of two extendable blankets of solar cells and the electricity they generate is delivered throughout the station using eight electrical buses, or channels, two per IEA.
The batteries in each IEA store power generated when the arrays are exposed to sunlight and then provide the electricity needed to keep the station operating during the lab's passes through Earth's shadow.
Spacewalks in 2017 and March 2019 replaced the 24 left and right inboard solar array batteries with 12 lithium-ion units.
For those replacements, the station's robot arm had the reach necessary to assist the astronauts with battery relocations and unbolting and only four spacewalks were required. The outboard arrays and batteries pose a more difficult challenge.
During two spacewalks last October and another two more this past January — which were NASA'sand — astronauts replaced the batteries at the far left end of the station's truss.
Because the outboard work site is so far from the robot arm's outermost anchor point, four spacewalks were required because the astronauts had to manually move batteries back and forth between a storage pallet and the integrated electronics assembly where they were installed.
Cassidy and Behnken plan to carry out four essentially identical spacewalks to replace the 12 nickel-hydrogen batteries in the outboard right-side set of arrays with six lithium-ion units.
During Friday's excursion, the astronauts removed five of the six older-generation batteries in one power channel, installed two new batteries and two adapter plates. During next week's spacewalk, the sixth nickel-hydrogen battery in the circuit will be removed and a third lithium-ion unit will be installed along with one more adapter plate.
During two spacewalks next month, Cassidy and Behnken plan to replace the final six old batteries in the right-side outboard truss segment and install the final three lithium-ion power packs.
But those spacewalks will depend in part on how the first two go and the status of plans to bring Behnken and Hurley back to Earth in the Crew Dragon ferry ship around Aug. 2. If problems crop up, the final two spacewalks could be deferred and carried out by a future station crew.