Prichal, with its six docking ports, would have served as the only permanent element of OPSEK, while other modules would come and go as their life span and mission required.

[5] In the mid-2000s, RKK Energia, the manufacturer of the Russian Orbital Segment (ROS) components, added the Uzlovoy Module (UM) to the future configuration of the ISS.

[2][8][9] Despite its small size, this four-ton, ball-shaped module could play an extremely important role in the Russian space program.

[1] In November 2018, executive director for Manned Space Programs of Roscosmos Sergei Krikalev indicated that Prichal was ready to fly, while there were still "little problems" with Nauka.

On 31 July 2021, technicians sent the spacecraft to the technical complex of the Baikonur Cosmodrome to continue assembly and pre-flight preparation in accordance with the schedule for the further development of the Russian segment of the International Space Station.

Over the next few months Prichal was checked out before the module was placed in a fairing and attached to a Soyuz 2.1b launch vehicle for delivery to the station.

[13] By early October 2021, Prichal had undergone tests of onboard automatic systems and the launch readiness simulation using ground diagnostics equipment.

On 11 October, specialists began powering up the module's onboard systems and bringing them to launch readiness using ground testing equipment.

The module and its space tug were then lowered into a horizontal position and moved into the anechoic zone, where tests of the spacecraft's KURS-NA radio system began on 20 October.

[14] On 12 October, the Soyuz 2.1b booster was assembled and moved to the erecting hall in perpetration for mating with Prichal and its service module.

[15] On 5 November, specialists conducted tests of solar panels aboard the Progress space tug by exposing them to an array of electric lights.

At the same time, the preparation of cargo items slated for delivery to the station aboard Prichal was in the final stages, according to Roscosmos.

[16] On 10 November, a meeting of technical management in Baikonur cleared the Progress M-UM space tug with the Prichal module for irreversible operations, including fueling and loading of pressurized gases to the composite spacecraft.

On 12 November, Roscosmos announced that a three-day process of pneumatic testing on all boosters comprising the Soyuz-2.1b launch vehicle for the Prichal mission had been completed.

On the same day, the resulting stack was transferred to Hall 102 inside the spacecraft processing building at Site 254 for installation of the protective fairing, which was performed on 16 November, thus completing the assembly of the payload section.

[23] On 23 November 2021, considered a backup day in the on-pad processing, specialists conducted checks of propellant lines in preparation for fueling of the launch vehicle.

[26] Upon completion of the joint tightness checks, the Russian crew members opened the transfer hatches and carried out the final operations to dismantle the docking mechanism, transfer the Progress power supply system to the unified station power supply, and mothball the cargo ship on 27 November 2021.

[citation needed] The ROSS is planned to be a completely new space station, without inheriting any module from Russian Orbital Segment of ISS.