On Wednesday 5th September at 11:06 GMT (1:34 p.m. EDT), astronauts Suni Williams of NASA and Akihiko Hoshide of JAXA accomplished their primary spacewalk objectives – on their second attempt – with a little help from a toothbrush. They completed the installation of a power unit on the station’s truss. This was their second spacewalk in a week, following an unsuccessful excursion on August 30, and lasted 6 hours and 28 minutes.
“You don’t just ‘go outside. Usually that is the fun and easy part of the entire thing,” said Flight Engineer Williams, going on to enumerate the many preparatory tasks that have been occupying her time since August 30: “suit sizing, tool gathering and preparation, equipment gathering and preparations, studying new procedures, reviewing and talking through how to get us suited and how to get the airlock depressed, reviewing the tasks we will do with each other and with the robotic arm, talking about cleaning up, and then talking thru a plan to get back into the airlock, and any emergencies that can come up — loss of communications, suit issues, etc.”
The astronauts’ main task was to install a new Main Bus Switching Unit (MBSU) on the s-zero truss. The MBSU is a 100 kg component which is used to relay power from the solar arrays to the systems onboard. These MBSU are essential electrical distribution boxes for the ISS. Prior to Wednesday’s spacewalk, the situation was far from ideal as the MBSU-1 was disconnected from the spacecraft. The spacewalkers were assisted from within the station by colleague Joe Acaba, who operated the Canadarm 2 robotic arm, following a robotics choreography prearranged by Acaba and Hoshide.
On the August 30th spacewalk Williams and Hoshide failed to install the MBSU due to a faulty bolt during the reinstallation process. Following the original trouble, they tethered the MBSU to the station and began troubleshooting the issue, resulting in what proved to be the 3rd longest space station spacewalk in history at 8 hours and 17 minutes. On this second spacewalk the pair managed to solve the issue by clearing the bolt hole obstruction with the makeshift tools of a toothbrush, some wire cleaner, and some nitrogen gas.
While the MBSU was disconnected the station was operating only on 6 of its 8 power channels at 75% power, but the loss of a further channel resulted in a further drop of 12.5% power. Flight Controllers were able to reroute power to critical systems to minimize the impact on station operations. With the successful completion of this spacewalk the station is back to 87.5% capacity and still in a safe configuration while options are being considered for repairing the remaining faulty power channel.
Below, the press conference that followed successful completion of Wednesday’s EVA: