Spacewalkers set the stage for future ISS additions
NASA astronauts Chris Cassidy and Bob Behnken completed their fourth spacewalk in less than a month to upgrade the International Space Station, setting the stage for future additions to the 20-year-old outpost.
Lasting 5 hours, 29 minutes, U.S. EVA-68 was dedicated to installing a robotics storage unit and preparing various locations for new parts for the outpost. This includes items such as a commercial research airlock and advanced solar arrays.
Spacewalkers replace batteries during first three outings
The first three spacewalks in this series each lasted around six hours and occurred on June 26, July 1 and July 16. Those, also performed by Cassidy and Behnken, were primarily focused on finishing a years-long process of replacing the aging nickel-hydrogen batteries on the station’s exterior truss with more-efficient lithium-ion batteries.
Those three spacewalks replaced batteries on the S6 truss segment. Previous spacewalks dating back to January 2017 focused on the P4, P6 and S4 truss segments. In total 48 nickel-hydrogen batteries were expected to be replaced with 24 lithium-ion units and 24 adapter plates. They were brought to the ISS in sets of six via four Japanese Kounotori spacecraft, the most recent, Kounotori 9, arrived in May 2020.
All but one lithium-ion battery was installed successfully. During a 2019 spacewalk, it was discovered that one of the new units failed. An older nickel-hydrogen battery was re-installed in its place while a future spacewalk is scheduled to install a new lithium-ion battery, which has since been delivered to the outpost.
It was expected the S6 truss battery replacement work would take four spacewalks. However, Cassidy and Behnken completed all of their tasks, plus some get-aheads, in only three outings. So the fourth spacewalk on July 21, 2020, was used to lay the groundwork for future spacewalks and hardware installation.
Once the duo opened the airlock and switched their space suits — Extravehicular Mobility Units — to battery power at 11:12 UTC, their first task was to install a new protective storage unit called Robotic Tool Stowage or RiTS on the Mobile Base System. Affectionately called the “robot hotel,” the device is designed to house equipment accessories for the Canadian Space Agency’s Dextre robotic “ hand,” also called the Special Purpose Dexterous Manipulator.
Video courtesy of Orbital Velocity
“RiTS provides thermal and physical protection for tools stored on the outside of station, not only freeing up room on board but also allowing the Canadian Space Agency’s Dextre robot to access them more quickly,” said RiTS Hardware Manager Mark Neuman in a July 21 NASA news release.
Two units of a tool called the Robotic Leak Locator, or RELL, were the first occupants to the RiTS robotic hotel, according to NASA
“RELL is a great example how robots with the right tools can simplify life for astronauts,” Neuman said. “Dextre can use RELL to detect ammonia leaks, eliminating the need for astronauts to perform the same task during a spacewalk.”
Both RiTS and RELL, as well as lessons learned in robotic servicing on the ISS, could be used on deep space destinations, such as NASA’s planned Lunar Gateway outpost later this decade.
H-fixture removal work
Once RiTS was installed and its occupants checked into their quarters, Cassidy and Behnken moved onto the second set of tasks, removing “H-fixtures” on the base of two solar arrays — mast canisters — on the port side of the ISS, according to NASA.
These were originally used for ground processing of the arrays before they were launched and are no longer needed. In their place is expected to be installed a piece of equipment to hold new solar arrays within the next several years.
Called iROSA, or ISS Roll Out Solar Array, these power-generating devices are designed to improve and augment the existing eight arrays, which collectively take up a space larger than an American football field. As they are aging — the oldest pair was launched in 2001 with the other three launched between 2006 and 2009.
Each iROSA is expected to be placed in front of the legacy arrays, according to NASA, and be attached via a modification kit installed onto the same mount the H-fixtures are on.
While each iROSA will shadow about two-thirds of the legacy arrays, the setup is expected to “increase power performance compared to the legacy ISS solar array.”
Ultimately, six iROSA devices will be delivered via three SpaceX Dragon cargo launches starting as early as 2021, according to NASA.
Only two H-fixtures were removed during U.S. EVA-68. A total of six need to be removed for all six iROSA modification kits to be installed.
One H-fixture was originally scheduled to be removed during the July 1 spacewalk. However, complications prevented its removal and required teams on the ground to re-evaluate their procedures and develop a way to pry them away from the canister.
Preparing for Bishop
The final major set of tasks planned for this spacewalk involved the removal of coverings on the port-side berthing cone on the Tranquility module. This was done to make way for a new commercial research airlock — NanoRacks’ Bishop airlock.
Bishop is designed to allow for large volumes of equipment to be transferred outside the outpost. This would include CubeSats and commercial and government-sponsored experiments, according to NASA.
This location was previously the home for the PMA-3 docking adapter. In 2017 it was moved to the space-facing port of the Harmony module to prepare for a second international docking adapter, which has since been installed.
Bishop is expected to be sent to the ISS inside the SpaceX CRS-21 mission as early as fall 2020.
Before heading in, the duo also routed Ethernet cables and removed a lens filter cover from an external camera, NASA said.
Overall, this was the 10th spacewalk for Cassidy and Behnken, four of which occurred in the last month.
Cassidy’s career spacewalking time now stands at 54 hours, 51 minutes. Behnken, meanwhile, is now at 61 hours, 10 minutes. This places them at ninth and fourth, respectively for most overall time spent outside a spacecraft.
The duo also tied the record for the most spacewalks ever conducted by NASA astronauts — 10 each. The others are Michael Lopez-Alegria and Peggy Whitson.
Additionally, this was the 231 spacewalk in support of ISS assembly and maintenance since 1998. According to NASA, spacewalkers have now spent a total of 60 days, 12 hours and 3 minutes outside the outpost.
Preparing to return to Earth
With these spacewalks completed, the next major milestone for Behnken is to return to Earth with Doug Hurley. The two launched to the ISS on May 30 inside the Demo-2 Crew Dragon capsule is to return to Earth. This was the first human spaceflight from Florida since July 2011.
Demo-2 is a test mission. While Hurley and Behnken helped augment the Expedition 63 crew, increasing its total size to five people, the duo’s other objectives were to evaluate Crew Dragon. This included, among other things, a habitability test with four people and a safe-haven test with the spacecraft sealed off from the outpost for 24 hours.
With all of the major objectives at the ISS completed, only one major thing remains for the Demo-2 crew — returning home.
As things stand now, the Demo-2 crew is expected to undock from the ISS on Aug. 1 and re-enter Earth’s atmosphere a day later on Aug. 2 to splash down off the coast of Cape Canaveral, Florida.
A successful splashdown will allow NASA to finish going over the results of the mission, certifying it for operational use. The first such mission is set to occur some six weeks after splashdown with the launch of the Crew-1 mission.
Crew-1 is slated to see NASA astronauts Michael Hopkins, Victor Glover and Shannon Walker, as well as Japanese astronaut Soichi Noguchi, fly to the ISS for a six-month stay.
Video courtesy of NASA
Derek Richardson has a degree in mass media, with an emphasis in contemporary journalism, from Washburn University in Topeka, Kansas. While at Washburn, he was the managing editor of the student run newspaper, the Washburn Review. He also has a website about human spaceflight called Orbital Velocity.