Early launch targets

Prichal module mockup

The Orbital Piloted Assembly and Experiment Complex (OPSEK), was a proposed Russian space station, intended to support deep space human exploration missions to Mars, possibly the Moon, and Saturn. It was planned to be partially constructed in orbit, while attached to the ISS. 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.^[3][8] In September 2017, Roscosmos stated that there "no plans to separate the Russian segment from the ISS". This ended public OPSEK plans.^[9]

Launch delays

ISS Russian orbital segment after docking of UM Prichal module

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. The proposal involves the addition of a Nodal Module (a significant modification of the Universal Docking Module (UDM) design, increasing the number of docking ports from 4 to 6 and taking into account its location at the Nauka nadir and at the same time reducing its weight from 20 tons to 4 tons, partly by removing the additional life-support system ^[10]) and adding two additional science/energy modules to the segment around 2013-2015. These plans were tabled, due to Nauka delays.^[11] Since the refurbishment of the Nauka module, the Uzlovoy module is now the Prichal module.^[6][12][13] Despite its small size, this four-ton, ball-shaped module could play an extremely important role in the Russian space program.^[3]

The preliminary design was completed on 15 January 2011, when RKK Energia announced that its Scientific and Technical Council (NTS), conducted a meeting which reviewed and approved the preliminary design of the Nodal Module and associated hardware. The meeting also approved the specialized launch craft, a Progress cargo ship designated the Progress M-UM and the adaptation of the Soyuz launch vehicle for the launch of the Progress M-UM spacecraft-module.^[8][3]

Initially, the nodal module was expected to be incorporated into the ISS in 2012, but the launch has been postponed several times because of the delays with Nauka, which had to be launched prior to Prichal.^[3] 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.^[14]

At the control and test station of the S.P. Korolev Rocket and Space Corporation Energia (part of the Roscosmos State Corporation), technical tests of the Prichal nodal module as part of the Progress M-UM transport cargo vehicle-module were completed. 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. The RSC Energia specialists successfully completed a cycle of joint tests of the Prichal module with the integrated mock-ups for the Zvezda service module and the Nauka multipurpose laboratory module. After the final operations, the undocked components of the spacecraft and ground test equipment were prepared for shipment to the cosmodrome by rail.^[15]

Processing at Baikonur

After the successful launch of Nauka module, on 11 August 2021, Prichal arrived at Baikonur after a four-day train ride from Energia in Moscow with its service module, Progress M-UM. The module was extracted from its container and placed in the hard stand that previously held Nauka while the propulsion module was moved over to Soyuz Test Stand 2 in hall 104 at Site 254. On the same day, specialists from RKK Energia installed the module and its progress in their respective processing rigs at Site 254 and began setting up the automated test network of the processing complex. As part of incoming inspection procedure, specialists conducted visual inspection of the propulsion module of Progress M-UM, and performed testing of the solar panel deployment mechanism on the vehicle. 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.^[16]

On 20 September 2021, Prichal was transferred to the vacuum chamber and testing was done. During the test, Prichal was filled with compressed helium to checked the hatches for leaks. Once testing was complete the wiring was installed and Prichal was returned to the vacuum for its pneumatic test in October 2021.^[17]

By early October 2021, Prichal had undergone tests of onboard automatic systems and the launch readiness simulation using ground diagnostics equipment. On 4 October 2021, the module was lifted from its work site and transferred to the processing rig for the Progress M-UM space tug, where it was connected to the adapter of the propulsion compartment of the Progress with mechanical locks. Further integration activities included connections and tests of power, command and data interfaces between the module and the space tug.

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 in horizontal position and moved into the anechoic zone, where tests of the spacecraft's KURS-NA radio system began on 20 October. On 28 October, Roscosmos announced that vacuum tests had been successfully completed.^[18]

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.^[19]

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 final stages, according to Roscosmos. These operations including loading of around 700 kg (1,500 lb) of cargo inside Prichal for the Expedition 66 crew aboard the station, including food, personal protective equipment, water filters, repair hardware, hygiene and medical supplies.^[20]

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. By that time, specialists were setting up another round of tests, checking onboard systems for monitoring propellant loading levels and conducting autonomous tests of the measurement system.

By 13 November, fueling operations for Prichal were completed and it was returned to the spacecraft processing building at Site 254.^[21] Later on that day, thermal protection blankets were added to the propulsion compartment and to all the ports, except the nadir and zenith port, of Prichal module.^[22]

The following day, the spacecraft was integrated with its launch vehicle adapter, which served as an interface for the payload fairing and provided connections from the command system aboard the Progress M-UM space tug and the Prichal module to the flight control system of the Soyuz 2.1b launch vehicle. After the docking of the components, specialists conducted test activations of the onboard radio complex and other service systems, Roskosmos said. 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] After installation and mechanical fixation of both fairing halves, the electrical circuits of the fairing separation system were checked.^[24]

On 18 November, it was transported to the launch vehicle assembly building at Site 31 for integration with the Soyuz-2.1b launch vehicle, which was completed by 19 November.^[25] The rollout of the vehicle to the launch pad at Site 31 started at 00:30 UTC on 21 November 2021.^[26]

Following the arrival at the pad, the vehicle was erected into vertical position and specialists began preparation for tests of the launch vehicle and the spacecraft. Integrated tests of the launch vehicle were conducted in the second half of the day on 22 November 2021 and were successfully completed with the simulation of the flight from launch until the separation of the payload.^[27] 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. The meeting of the State Commission, overseeing the preparations for launch, was scheduled at 09:00 UTC (10:00 Baikonur time), clearing the launch vehicle for fueling and launch.^[28]

Multi-docking compartment

It is standard practice to dock Soyuz vehicles to the nadir ports of Rassvet and Prichal and dock Progress to the aft port of Zvezda and the zenith port of Poisk. This is because the transfer chamber which connects to Zvezda's aft port has a small leak which requires the hatches to remain closed as much as possible, which would block access to a Soyuz if it were docked to Zvezda's aft port. In addition, Progress crafts are preferred for the aft port as this enables them to perform ISS reboosts using their main engines. Progress crafts are also preferred for the Poisk zenith port as Poisk is now serving as the Russian Segment's EVA airlock following the departure of Pirs, and access to Soyuz craft docked to Poisk is blocked whilst Poisk is depressurized during spacewalks, which presents safety issues in an ISS evacuation scenario.^[38]

Space agency websites

• Russia (Energia)
• Russia (Federal)