The ISS, now in its twenty-first year of continuous human occupation, has had a busy year of operations. Two new modules were added and 18 visiting vehicles were at the Station throughout the year. In total, 23 humans called the orbiting outpost home in 2021.

Russian Orbital Segment expansion

This year marked the completion of the Russian Orbital Segment – shortened to ROS – with the arrival of Nauka and Prichal, the first of which replaced the Pirs module.

Pirs, also known as Docking Compartment-1, arrived at the ISS on September 17, 2001. It served as the primary airlock module for the Russian segment prior to its decommissioning.

Pirs leaving the Station with Progress MS-16. (Credit: NASA)

A series of two Russian spacewalks occurred to decommission Pirs prior to departure. The first occurred in November 2020. The second spacewalk – performed by cosmonauts Oleg Novitsky and Pytor Dubrov – occurred in June 2021 and successfully moved the Strela crane to the Poisk module and removed docking antennas on Pirs.

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Progress MS-16 – a cargo resupply spacecraft – undocked from the Station on July 26th, bringing Pirs along with it. Progress had originally docked to Pirs on February 17th. For its undocking, instead of simply undocking from Pirs, the latches holding Pirs to the rest of the Station were unhooked, allowing Progress to carry the old module away from the Station.

Both Progress and Pirs then reentered the atmosphere and were destroyed the same day. In total, Pirs spent 19 years on the ISS.

The departure of Pirs and Progress occurred after the successful launch of the Nauka Multipurpose Laboratory Module (MLM) which launched on July 21 on a Proton-M rocket from Baikonur.

Overcoming communications and propulsion issues, Nauka finally docked to the nadir – or Earth-facing – port on Zvezda on July 29. Hours after docking, a software glitch on Nauka caused the module’s thrusters to fire – causing the Station to rotate about one and a half full rotations. Thrusters on the Zvezda module and Progress MS-17 were brought online to regain control, and Nauka’s engines were deactivated.

Contact and capture, docking confirmed. At 9:29am ET, the @Roscosmos Nauka science module arrived at the Earth-facing side of the @Space_Station‘s Russian segment: pic.twitter.com/svwaYm5UGS

— NASA (@NASA) July 29, 2021

Following docking, the first of two Russian spacewalks to integrate and outfit the new module occurred on September 3 by Novitsky and Dubrov. The following Extra-Vehicular Activity (EVA) occurred on September 9. Both EVAs installed ethernet cables, connecting Nauka with both the US Orbital Segment (USOS) and Zvezda. They were also able to install EVA handles on Nauka.

Soyuz MS-18 became the only Soyuz spacecraft to dock to the nadir port on Nauka on September 28, before undocking the following month. Progress MS-17 later docked to the module and departed on November 25, taking with it a temporary docking adaptor – freeing the port for Prichal.

Russia’s Prichal module then docked to the nadir port on November 26, while attached to Progress M-UM – a modified Progress propulsion section that maneuvered and docked Prichal to the Station. Prichal is a “Nodal” module, meaning it is spherical in nature and features six docking ports. This will allow for future expansion of the Russian segment, or for additional visiting vehicles to dock at the Station.

The Prichal module – the white sphere in the center – docked to the ISS, with its Progress M-UM tug still attached. Credit: NASA

The Progress M-UM tug then detached from Prichal on Dec. 23, completing the ROS expansion. Prichal is now available for visiting vehicles to dock with.

US Orbital Segment expansion

During the year, a number of spacewalks were conducted to install the first pair of ISS Roll-Out Solar Arrays – iROSAs for short.

Several spacewalks occurred in 2021 prior to the installation of the iROSA solar arrays, which included work on the Bartolomeo platform and the installation of new lithium-ion batteries.

The first iROSA was installed on ISS US EVA-75 on June 20. Crew-2 crew members Shane Kimbrough and Thomas Pesquet deployed the new solar array on the P6 truss. The new array was connected to the 2B power channel.

Deployment of the array was delayed due to issues on ISS US EVA-74 on June 14.

The iROSA solar arrays are based upon the ROSA that was tested on the ISS on June 18, 2017. The ROSA was delivered on a SpaceX Cargo Dragon during the CRS-11 mission and was later released from the ISS. Notably, NASA’s DART spacecraft also features two ROSAs.

Each iROSA is 63 feet long and 20 feet wide, compared to the heritage ISS solar arrays which are 115 feet long and 38 feet wide. The iROSA solar arrays each produce 23 kW of power, which supplements the existing heritage arrays that have degraded since deployment.

ROSA Deploy! (Second ROSA).

Play by Play: https://t.co/zrQSPSluLW pic.twitter.com/5RJOQWQuGD

— Chris Bergin – NSF (@NASASpaceflight) June 25, 2021

A second iROSA was installed on June 25 during ISS US EVA-76. Both Kimbrough and Pesquet participated in the EVA. The new iROSA was installed on the 4B power channel, located on the P6 truss, near the array installed in the prior spacewalk.

During ISS US EVA-77 on September 12, Pesquet and Akihiko Hoshide installed the 4A modification kit to the P4 truss, which will eventually support an iROSA array. CRS-25 is scheduled to deliver the iROSA for the P4 truss in 2022, which will be the last iROSA on the port side of the ISS.

The final EVA of the year was conducted by Crew-3 members Thomas Marshburn and Kayla Barron on December 2. Both were able to remove a broken S-band antenna on the P1 truss and replace it with a spare antenna.

Russian ASAT test

On November 15, an A-235 PL-19 Nudol anti-satellite missile was fired from the Plesetsk Cosmodrome in Russia for an apparent anti-satellite weapons test by the Russian military. The missile intercepted and destroyed a defunct Tselina-D electronic signals intelligence (ELINT) satellite, designated as Kosmos-1408.

The destruction of this satellite created 1,500 pieces of orbital debris, which spread out along the orbit caused a debris cloud. The debris crossed over into the orbit of the ISS over different periods in 90-minute intervals.

In response to the event, ISS mission control instructed the Expedition 66 crews to begin “safe haven activities” – during which the crew powered up and sheltered in their respective spacecraft, which included Crew Dragon Endurance (Crew-3) and Soyuz MS-19.

After the time of “highest risk” was over, the crews were able to reenter the ISS. However, the hatches on radial modules, including Columbus and Kibo, remained closed for a number of days until the risk further diminished.

The event sparked responses from members of the international community, including the US and the European Union.

Visiting vehicles of 2021

In 2021, a total of seven crewed missions arrived and/or departed the Station. This included Soyuz MS-17, Crew-1, Soyuz MS-18, Crew-2, Soyuz MS-19, Crew-3, and Soyuz MS-20.

In the spring, the Crew-1 and Crew-2 missions had a direct handover – where both crews are on the Station together for a short time – while in the fall delays led to an indirect handover between both Crew-2 and Crew-3 missions on the ISS. During the departure of the Crew-2 mission, Crew Dragon Endeavour conducted a fly-around of the ISS, providing new photos of the orbiting outpost.

Also in the spring, Soyuz MS-18 launched to the ISS for a direct handover with the Soyuz MS-17 crew, who later departed the Station in April. Soyuz MS-18 undocked in the fall with two spaceflight participants and one cosmonaut.

Both Pyotr Dubrov, and Mark Vande Hei have had their stays on the ISS extended, as they launched on Soyuz MS-18 in April of 2020 and will land on Soyuz MS-19. Upon landing they will have been in space for almost a year.

Below is a table of all visiting vehicles that were part of the ISS this year.

Spacecraft
Launch
Docking 
Undocking

Progress MS-15
July 23, 2020
July 23, 2020
Feb. 9, 2021

Soyuz MS-17
Oct. 14, 2020
Oct. 14, 2020
Apr. 17, 2021

Dragon Resilience (Crew-1)
Nov. 16, 2020
Nov. 17, 2020
May 2, 2021

CRS-21
Dec. 6, 2020
Dec. 7, 2020
Jan. 12, 2021

Progress MS-16
Feb. 15, 2021
Feb. 17, 2021
July 26, 2021

NG-15
Feb. 20, 2021
Feb. 22, 2021
June 29, 2021

Soyuz MS-18
Apr. 9, 2021
Apr. 9, 2021
Oct. 17, 2021

Dragon Endeavour

(Crew-2)

Apr. 23, 2021
Apr. 24, 2021
Nov. 8, 2021

CRS-21
June 3, 2021
June 5, 2021
July 8, 2021

Progress MS-17
June 29, 2021
July 2, 2021
Nov. 25, 2021

NG-16
Aug. 10, 2021
Aug. 12, 2021
Nov. 20, 2021

CRS-23
Aug. 29, 2021
Aug. 30, 2021
Sept. 30, 2021

Soyuz MS-19
Oct. 5, 2021
Oct. 5, 2021
March 2022 – On Orbit

Progress MS-18
Oct. 28, 2021
Oct. 30, 2021
On Orbit

Dragon Endurance

(Crew-3)

Nov. 11, 2021
Nov. 11, 2021
Apr. 2022 – On Orbit

Progress M-UM
Nov. 24, 2021
Nov. 26, 2021
Dec. 22, 2021

Soyuz MS-20
Dec. 8, 2021
Dec. 8, 2021
Dec. 19, 2021

CRS-24
Dec. 21, 2021
Dec. 22, 2021
On Orbit

Tourism flights

Soyuz MS-19 marked the first of two missions flying with spaceflight participants, instead of professional astronauts. The mission launched on a Soyuz 2.1a rocket on October 5 and subsequently docked to the Rassvet module the same day.

The Soyuz crew consisted of spaceflight participants Yulia Peresild and Klim Shipenko along with cosmonaut Anton Skaplerov. Both Peresild and Shipenko visited the Station to film a Russian movie called “The Challenge,” where Peresild was the actor and Shipenko was the director.

Peresild and Shipenko returned to earth on Soyuz MS-18 along with cosmonaut Oleg Novitsky on October 17.

Over a month later, Soyuz MS-20 launched on December 8 with Japanese spaceflight participants Yusaku Maezawa and Yozo Hirano along with Roscosmos cosmonaut Alexander Misurkin.

A precedent for the current Soyuz launch was created two months ago, when the crew had a commander — a professional cosmonaut and two non-professional spaceflight participants.

Then Peresild and Shippenko together with @Anton_Astrey were launched to the stars on the Soyuz MS-19 pic.twitter.com/UOmy4H6IgI

— РОСКОСМОС (@roscosmos) December 8, 2021

After arriving and docking to the Poisk module on the same day, the crew of three spent 11 days on the space station. Maezawa was filmed in multiple locations on the Russian segments in videos posted to social media. Maezawa bought his and Hirano’s seats through space tourism company Space Adventures.

Soyuz MS-20 later landed on December 20.

Both Soyuz MS-19 and Soyuz MS-20 were built so that the single cosmonaut could alone pilot and fly the Soyuz spacecraft, decreasing the amount of time needed for training for the spaceflight participants.

Looking forward to 2022

Axiom Space and SpaceX are targeting February 28 to launch a crew to the ISS on a SpaceX Crew Dragon. The mission, known as Axiom-1 or AX-1, will consist of former NASA astronaut Michael López-Alegría, American Larry Connor, Canadian Mark Pathy, and Israeli Eytan Stibbe.

Axiom-1 will be the first all-private crewed mission to the ISS.

The follow-up Axiom mission, Axiom-2, is planned for no earlier than (NET) fall of 2022. The mission will be commanded by former NASA astronaut Peggy Whitson, and the crew will also include John Shoffner.

Both missions are being flown for Axiom Space. The company is also building the first private space station, which will be built as part of the ISS.

Rendering of the ISS, featuring the planned Axiom segment on the left. Credit: Mack Crawford for NSF

The next Soyuz crew to launch to the ISS will be an all-Russian crew consisting of cosmonauts Oleg Artemyev, Denis Matveev, and Sergey Korsakov. The mission is planned to launch on Soyuz MS-21 in March.

The current Soyuz mission, Soyuz MS-19 – with Roscosmos cosmonauts Anton Shkaplerov, Pyotr Dubrov, and NASA astronaut Mark Vande Hei – is scheduled to return in March.

The NASA/SpaceX Crew-4 mission is currently slated for launch in April of 2022 and will transport NASA astronauts Kjell Lindgren, Robert Hines, and Jessica Watkins along with ESA astronaut Samantha Cristoforetti of Italy to the ISS.

Boeing and NASA are also targeting the launch of Starliner’s Orbital Flight Test-2 (OFT-2) in 2022, following an issue with valves in the service module discovered earlier in 2021. The current estimated flight date is in May, however, that is subject to hardware investigations and the Station’s ever-busy visiting vehicle schedule.

(Featured image: The ISS is seen from Crew Dragon Endeavour during the Crew-2 fly around after departure. Credit: NASA)

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