Outside the International Space Station (ISS), Oleg Novitsky and Pyotr Dubrov have completed a near 7 hour extravehicular activity, or EVA/spacewalk, to finalize external preparations for the removal to the Pirs docking compartment that has served the Station for nearly 20 years.
Delivered in 2001, Pirs will be removed from the ISS no earlier than 17 July 2021 to make room for the new Nauka science module on the Russian segment of the outpost.
Officially beginning at 05:53 UTC/01:53 EDT, the 2 June spacewalk saw the two Russian cosmonauts leave the Poisk module — also known as Mini-Research Module 2 (MRM2) — with a variety of tasks.
The main focus, however, was completion of decommissioning activities related to the Pirs docking compartment, work that was successfully completed across several orbits of the Earth.
After leaving the airlock of the Station’s Poisk module, Novitsky and Dubrov expertly worked through a variety of small issues that are not altogether uncommon on spacewalks — such as bolts not behaving as expected.
First up, the two cosmonauts took a pressurized container out of the airlock with them and temporarily installed it on the Zarya module. From there, they were able to remove a failed fuel flow regular on Zarya and seal it inside the pressurized container — which was unbolted later in the EVA and jettisoned, or thrown, overboard for natural decay and destruction in Earth’s atmosphere.
PET 6hrs 20mins. Pirs is now officially decommissioned ahead of being undocked by a Progress vehicle and sent to its doom via a (controlled) destructive re-entry. pic.twitter.com/bZYRbyKxQm
— Chris Bergin – NSF (@NASASpaceflight) June 2, 2021
SpaceX
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This type of “throw-it-away” element for Station spacewalks/repairs is somewhat common on both the Russsian and US-European-Canadian-Japanese-segments for elements that are either too large or too hazardous to be brought back into the Station or that can’t be taken away by visiting cargo craft.
Novitsky and Dubrov then moved the Strella crane from Pirs and firmly attached it to Poisk while also working to disconnect the cabling that has allowed the module’s critical KURS automated rendezvous system to function.
With Progress MS-16 already docked to Pirs in preparation for the module’s removal, the automated docking system is no longer needed.
The cables were carefully disconnected from Pirs and temporarily reconnected to the Zvezda module, where controllers in Mission Control Moscow were able to test them and confirm they were still functioning.
After the Nauka module arrives later this year, another spacewalk will reconnect the cables to Nauka’s rendezvous system to bring its docking port online.
Work then continued with the cosmonaut duo removing a gap spanner between Pirs’ spacewalk ladder and Zvezda. Once that task was complete, Pirs was considered “decommissioned” — the first ISS module to reach this status.
Now Petr and Oleg have time to rest for a while. All the connectors are connected to the transfer compartment of the Zvezda module. pic.twitter.com/IzVB70ZHwt
— Katya Pavlushchenko (@katlinegrey) June 2, 2021
Mission Controllers near Moscow then evaluated the EVA’s timeline and concluded that the final task could go ahead as planned from a timeline and crew fatigue standpoint — with both Novitsky and Dubrov noting they felt fine to continue.
This final activity saw the cosmonauts install two experiment packages outside Poisk, including one to study microflora and another to monitor a variety of materials and the effects on them of the low Earth orbit environment.
With those experiments installed, Novitsky and Dubrov collected their tools and reentered the Poisk module. With hatch closure, the two completed the sixth ISS EVA of the year at the International Space Station and the 238th spacewalk overall in support of the outpost.
Russian EVAs are timed from hatch open to hatch close; as such, Poisk’s hatch was closed at 13:12 UTC/09:12 EDT, concluding the venture at a Spacewalk Elapsed Time of 7 hours 19 minutes.
If all goes to plan, the module that will take Pirs’ docking place on the Station will launch no earlier than 15 July on a Proton rocket from the Baikonur Cosmodrome in Kazakhstan. Once Nauka is safely in orbit and initial checkouts are performed and the health of the module is confirmed, Russian mission controllers will use the Progress MS-16 cargo craft to remove Pirs from the Station.
The module’s removal will be a somewhat mirror of its arrival. Launched with a modified Progress propulsion section, Pirs autonomously docked to the Zvezda service module’s nadir, or Earth-facing, port before the modified Progress propulsion unit undocked itself from Pirs and flew away.
The Nauka module, in preparation for launch in 2021. (Credit: RSC Energia)
Now, the entire Progress MS-16 craft, which launched on 15 February 2021 and delivered thousands of kilograms of supplies to the Station, will be used to remove Pirs. Instead of commanding the hooks connecting Progress to Pirs to retract, the docking hooks that have held Pirs to Zvezda for 20 years will be commanded to retract instead, and Progress will pull Pirs away from the Station as it leaves.
In this way, Progress MS-16 will not undock from the Station, but rather Pirs will undock — with Progress MS-16 then maneuvering the still-mated pair away from the ISS before safely deorbiting the module for a destructive end-of-life plunge into Earth’s atmosphere.
A few days later, Nauka will maneuver itself up to the ISS, rendezvous, and dock itself to the now-vacant port on Zvezda.
Meanwhile, prior to Pirs’ departure and Nauka’s arrival, the seventh and eight EVAs of the year will occur later this month when European Space Agency astronaut Thomas Pesquet and NASA astronaut Shane Kimbrough conduct two spacewalks from the Quest airlock to install the first two IROSA, International Space Station Roll-Out Solar Arrays.
The new arrays will boost the ISS’s power generation capability, which has naturally been decaying since the original set of eight solar array wings were delivered between December 2000 and March 2009 over the course of four Space Shuttle missions: STS-97/Endeavour, STS-115/Atlantis, STS-117/Atlantis, and STS-119/Discovery.
In all, the six new arrays from Boeing, the first two sets of which are scheduled to launch no earlier than Thursday, 3 June on SpaceX’s CRS-22 mission of Cargo Dragon, will bring the ISS back to near-full power capacity and set the stage for a major scientific and physical expansion effort on the US-segment of the Station, which includes Japan, Europe, and Canada as well.
The efforts on both sides of the Station mark the the most intense construction efforts on the outpost since initial US assembly of the ISS were completed by the STS-134/Endeavour crew exactly 10 years ago in June 2011 with the handoff of Endeavour’s Orbiter Boom Sensor System (OBSS) on the Orbiter’s 25th and final mission.
Lead image: Novitsky and Dubrov working outside Poisk. Credit: NASA
