Orbital Piloted Assembly and Experiment Complex

Around the predicted decommissioning of the International Space Station in the late 2020s, the Russian Federal Space Agency (Roscosmos) developed a concept in 2009 to construct a successor station in low Earth orbit.[1][2]

The 2009 concept considered re-using several ISS modules to form the initial parts of a new station, which were to be subsequently replaced by new modules.[4] On 17 June 2009, Roscosmos officially informed its ISS partner NASA about its intention to "build and prepare for operation the first elements of the orbital assembly and experimental piloted space complex by the end of the ISS life cycle".[4] As of 2017, those plans had been abandoned, and the new station was to be composed entirely of new purpose-built modules.[3]

According to the Russian crewed spaceflight contractor RKK Energia, the new station must be able to perform the following tasks:[5]

• Large spacecraft assembly
• Flight tests and launches
• Creating, servicing and completing inter-orbital tugs
• Providing medical and biological conditions required for the rehabilitation of interplanetary expedition crews after their return to Earth orbit.

Annotated image of the International Space Station's Russian Orbital Segment configuration as of 2011

OPSEK was to have followed the Salyut and Almaz series, Kosmos 557, and Mir as the 12th Russian space station launched. OPSEK is a third generation [6] modular space station.[7]

Examples of other modular stations include the former Soviet/Russian Mir, the International Space Station, and the proposed Chinese space station. The first space station, Salyut 1, and other one-piece or "monolithic" first generation space stations, such as Salyut 2, 3, 4, 5, DOS-2, Kosmos 557, Almaz, and NASA's Skylab station, were not designed for re-supply.[8] Generally, each crew had to depart the station to free the only docking port for the next crew to arrive. Skylab had more than one docking port but was not designed for resupply. Salyut 6 and 7 had more than one docking port and were designed to be resupplied routinely during crewed operation.[9] Modular stations can allow the mission to be changed over time and new modules can be added or removed from the existing structure, allowing greater flexibility.

Rassvet, left of center with the Russian science airlock temporarily stored on its side.

Computer generated image of the Russian Orbital Segment after Nauka docking

Expected Russian Orbital Segment modules around the time of OPSEK separation (2020 or later) arranged by launch dates:[10]

• 2000: Zvezda (DOS-8) - potential part of OPSEK.[11]
• 2009: Poisk (MRM-2) - potential part of OPSEK - Poisk (Russian: По́иск; lit. Search), also known as the Mini-Research Module 2 (MRM-2), Малый исследовательский модуль 2, or МИМ 2. Poisk is a Russian airlock module with two identical hatches. Its predecessor, Pirs, is used to store, service, and refurbish Russian Orlan suits. The outermost docking ports on both airlocks allow docking of Soyuz and Progress spacecraft, and the automatic transfer of propellants to and from storage on the station.[12]
• 2020: Nauka (FGB-2) - to form part of OPSEK - Nauka (Russian: Нау́ка; lit. Science), also known as the Multipurpose Laboratory Module (MLM) or FGB-2, (Russian: Многофункциональный лабораторный модуль, or МЛМ), is the major Russian laboratory module. This module will be separated from the ISS before de-orbit with support modules to become the OPSEK space station. It contains an additional set of life support systems and orientation control. Nauka's mission has changed over time; during the mid-1990s it was intended as a backup for the first FGB, and later as a Universal Docking Module (UDM). Its docking ports will be able to support automatic docking of both spacecraft, additional modules and fuel transfer. Prior to the arrival of the MLM, a Progress robotic spacecraft will dock with the International Space Station Pirs module, depart with that module, and both will be discarded. Nauka will then use its own engines to attach itself to the ROS after 2014.[13] The European Robotic Arm, which will service the Russian Orbital Segment, will be launched alongside the MLM.[14]
• 2020: Uzlovoy Module - to form part of OPSEK - Node Module (UM)/(NM). This 4-ton ball shaped module will support the docking of two scientific and power modules during the final stage of the station assembly and provide the Russian segment additional docking ports to receive Soyuz TMA (transportation modified anthropometric) and Progress M spacecraft. NM is to be incorporated into the ISS in 2016. It will be integrated with a special version of the Progress cargo ship and launched by a standard Soyuz rocket. The Progress would use its own propulsion and flight control system to deliver and dock the Node Module to the nadir (Earth-facing) docking port of the Nauka MLM/FGB-2 module. One port is equipped with an active hybrid docking port, which enables docking with the MLM module. The remaining five ports are passive hybrids, enabling docking of Soyuz and Progress vehicles, as well as heavier modules and future spacecraft with modified docking systems. More importantly, the node module was conceived to serve as the only permanent element of OPSEK. Equipped with six docking ports, the Node Module would serve as a single permanent core of the future station with all other modules coming and going as their life span and mission required.[15][16] Uzlovoy will be launched after Nauka MLM; launch dates will be 2022 or later.[17]
• 2022: Science and Power Module 1 (NEM-1) - to form part of OPSEK.[18]

• OPSEK information page
• Presentation.pdf, by Head of Russian Federal Space Agency, 17 June 2009
• Roscosmos YouTube channel
• RSC Energia: Science Research on ISS Russian Segment
• European Space Agency
• Russia (Energia)