Expedition 63 Commander Christopher Cassidy and Joint Operations Commander Robert Behnken, both NASA astronauts, completed the three and a half year process of upgrading the International Space Station’s power systems during a spacewalk on July 21st.
The spacewalk, designated US EVA-68, marked the 10th EVA for both astronauts, who have each accumulated over 50 hours of spacewalking time each during their respective careers.
Upon exiting the Quest airlock, Cassidy and Behnken’s EVA-68 marked the 12th and final in a series of spacewalks to replace all of the aging Nickel-Hydrogen (Ni-H2) batteries located on the outside of the ISS with newer Lithium-Ion batteries.
The effort to replace the batteries began in January 2017 when Expedition 50 astronauts Shane Kimbrough and Peggy Whitson ventured outside to begin the labor-intensive process on the S4 Truss segment.
In the three and a half years since, NASA and International astronauts have carried out nine more EVAs as part of the replacement efforts, fully replacing the older batteries on the S4, P4 and P6 truss segments and leaving just the S6 Truss remaining.
Chris Cassidy, who launched aboard Soyuz MS-16 in April of this year, and Behnken, who launched the following month aboard SpaceX’s Crew Dragon Demo-2 mission, had already completed two spacewalks focusing on the replacement of batteries on the S6 Truss element’s 1B electrical channel before moving on to the 3B power channel — work that completed today.
The first of those two spacewalks for the 1B power channel occurred on June 26th, with the second following on July 1st.
Each truss segment contains two power channels, each with its own solar arrays and set of batteries. Cassidy and Behnken’s first two EVAs successfully completed replacement of all six batteries of the 1B power channel on the S6 Truss.
Behnken and Cassidy began work on the 3B power channel on the S6 truss last week with the goal of removing five of six 3B channel Ni-H2 batteries followed by installation of the first three lithium-ion batteries.
Cassidy and Behnken worked so far ahead of the planned timeline on that spacewalk that they were actually able to remove all six Ni-H2 batteries instead of just the five per the original plan — which officially completed removal of all Ni-H2 batteries from the Station’s power systems.
With the spacewalk successful, it marked the penultimate EVA in the effort to upgrade the batteries on the ISS.
The final spacewalk, EVA-68, took place July 21st and saw Behnken and Cassidy complete the battery and electrical work, bringing an end to the three and a half year process.
Cassidy and Behnken also performed a host of other tasks on this EVAs, including — among other things — routing and connecting ethernet cables for external experiment data transmission to scientists.
Behnken during the second EVA of STS-130, 2010. (Credit: NASA)
Toward the end of the spacewalk, Behnken and Cassidy made their way down from the S6 truss towards the Node 3/Tranquility module in order to prepare the module for installation of the commercially built Bishop cubesat airlock module, which will be used to deploy small satellites from the ISS.
NanoRacks, an American company that has built several technologies utilized today aboard the ISS, have developed Bishop alongside Thales Alenia Space and Boeing, and are set to see it launched in October this year as un-pressurized cargo aboard SpaceX’s Commercial Resupply Services-21 (CRS-21) mission — the first flight of SpaceX’s upgraded Cargo Dragon 2 spacecraft.
Although the Bishop airlock was not installed during EVA-68, the tasks at Node-3/Tranquility were important in preparing the module for installation of the small airlock, which should occur shortly after its arrival on CRS-21.
For both this EVA, Behnken served as EV-1 (lead spacewalker), wearing red stripes on his Extravehicular Mobility Unit (EMU, or spacesuit), while Cassidy served as EV-2, wearing no stripes on his EMU.
As with the previous three spacewalks, Crew Dragon Demo-2 Spacecraft Commander and Expedition 63 crewmember Doug Hurley supported the EVA from inside the Station, helping the two EV crew members suit up, as well as controlling the robotic elements of the excursion from inside the outpost’s Cupola module at the Robotics Work Station.
Expedition 63 following the arrival of Crew Dragon Demo-2. (Credit: NASA)
Roscosmos cosmonauts Anatoli Ivanishin and Ivan Vagner, both Expedition 63 Flight Engineers, will also lend a hand in EVA preparations.
Today’s activities mark the 231st spacewalk dedicated to assembly and maintenance of the International Space Station.
With EVA-68, Behnken and Cassidy have amassed 10 spacewalks each, joining former NASA astronauts Michael Lopez-Alegria and Peggy Whitson with the most spacewalks by Americans.