Roscosmos completes the Russian assembly by attaching a new docking node to the station.

Roscosmos has successfully docked a new docking node module to the International Space Station (ISS) after launching it to the station on Wednesday, November 24 at 13:06 UTC / 8:06 a.m. EST.

The module will expand the Russian Segment's docking ports, and it is the outpost's final Russian model.

The original design for the Russian segment of the International Space Station (ISS) included a Universal Docking Module (UDM) to increase the number of docking ports available for future modules.

Due to budget constraints, this module was canceled early in the ISS program.

The UDM concept, however, spawned a new proposal for a Nodal Module (NM), which would give the Russian Segment expansion options because all of its docking ports were either in use or reserved for visiting spacecraft.

The Prichal ("pier") node is a departure from the previous Russian station design concept, which typically consisted of a core module (Zvezda in the case of ISS) with an attached spherical docking compartment to which all other modules were docked.

This means that as the core module ages and its systems fail, there is no choice but to rebuild the station from the ground up, even if the other modules are newer and fully functional.

The Node Module concept separates the spherical docking compartment from the core module and turns it into a stand-alone component.

The idea is that all station modules would dock to the Node Module, allowing each module to be replaced without having to undock them all.

In this sense, Prichal is the Russian equivalent of the Node modules found on the station's American segment.

Originally, it was planned that two Science

However, Roscosmos announced in April 2021 that the NEMs would no longer be part of the ISS and would instead be part of a new Russian space station for which a new Node Module would be built.

While Roscosmos has since walked back on those statements, given the Russian space program's budgetary realities and the ISS's remaining lifespan, it is unlikely that any additional modules will ever be docked to Prichal.

As a result, while Prichal is an intriguing module in many ways, it is already essentially a module without a purpose because it does not add any new capabilities to the ISS beyond what it already has.

Prichal is a spherical module with six docking ports - two axial and four radial - in total.

The docking ports are hybrid in design, combining the Androgynous Peripheral Attachment System (APAS) with the SSVP probe.

Although the docking collar is similar to the APAS design, the initial capture is done with a probe.

The hybrid system's goal is to provide a larger hatch passageway for permanent modules.

Prichal's zenith docking port is an active hybrid port with a probe that allows it to dock to the International Space Station.

The remaining five ports are hybrid passive ports with drogues that allow other modules to dock to them.

Prichal's nadir docking port has a special adapter called SSPA-GM that allows the hybrid docking system to be converted to one that works with the SSVP probe.

This adapter converts the nadir hybrid port's APAS docking collar to an SSVP docking collar while keeping the same docking drogue for initial capture.

This will allow Soyuz and Progress vehicles to dock at Prichal's nadir port, allowing the Russian Segment's four docking ports to remain open to visiting vehicles.

If a new module were to dock to Prichal, this adapter would have to be removed by a departing Progress spacecraft in order to return the nadir port to a hybrid configuration (with an APAS docking collar) in order for the new module to dock.

However, this would make the nadir port of Prichal unavailable for Soyuz and Progress dockings, reducing the number of Russian visiting vehicle ports to three.

Lyappa arm sockets are also included in Prichal.

Future modules arriving at Prichal will dock to the nadir port, as docking to any of the axial ports would cause issues with approach corridors and rotational loads.

The Lyappa arm, which would extend from the module and connect to a corresponding socket on Prichal, would then relocate the newly arrived module to an axial port.

The module would then be rotated and swung from the nadir port to the axial port by the Lyappa arm.

On the Mir space station, Lyappa arms were used, and the new Chinese station uses a similar concept.

The last time a Lyappa arm was used on-orbit was in April 1996 for the Priroda module's post-docking relocation.

For launch, Prichal was attached to a Progress spacecraft's modified propulsion segment, which will perform all rendezvous and docking maneuvers.

Progress M-UM, the specially modified propulsion segment, is essentially a Progress spacecraft with Prichal installed in place of the pressurized cargo compartment.

After delivering Prichal to the International Space Station, Progress M-UM will separate from Prichal and perform a destructive re-entry.

In 2001 and 2009, the Pirs and Poisk modules were delivered to the International Space Station using the same concept.

At 13:06 UTC / 8:06 am EST, Prichal was launched from Kazakhstan's Baikonur Cosmodrome atop a Soyuz 2.1b booster.

Prichal communicated down that everything was fine after separation from the Blok-I stage once in orbit, and the module began a two-day rendezvous with the ISS.

On Thursday, November 25, the Progress MS-17 spacecraft undocked from the Multipurpose Laboratory Module (MLM) Nauka's nadir docking port, taking with it an SSPA-GM Hybrid-to-SSVP docking collar adapter, the same type featured on Prichal.

This adapter was installed on Nauka's hybrid nadir port in order for Soyuz and Progress vehicles (which use the SSVP system) to dock there.

This was done as an "insurance policy" in the event that Prichal failed to reach orbit.

The adapter was removed by the departing Progress MS-17 only after Prichal was safely in orbit and on its way to the ISS, converting Nauka's nadir port back to hybrid configuration and making it ready to receive Prichal.

On Friday, November 26 at 15:19 UTC / 10:19 EST, Prichal docked at the Nauka nadir port, using the automated Kurs rendezvous system.

Following the leak checks, the hatch will be opened in the days ahead.

On December 21, the Progress M-UM propulsion segment will be separated from Prichal, and a Russian spacewalk will be performed on January 19 to connect cables between Nauka and Prichal.

On March 18,2022, the Soyuz MS-21 mission is scheduled to dock at Prichal for the first time.

(Photo courtesy of NASA: Prichal docks with the International Space Station.)

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