The Russian Orbital Segment (ROS) is the name given to the components of the International Space Station (ISS) constructed in Russia and operated by the Russian Federal Space Agency (Roskosmos). The ROS handles Guidance, Navigation & Control for the entire Station.
The segment currently consists of five modules, which together essentially comprise the base configuration of the cancelled Russian space station Mir-2. The segment is controlled directly from Roskosmos's Mission Control Center in Moscow.
The first module, Zarya, otherwise known as the Functional Cargo Block or FGB, was the first component of the ISS to be launched, and provided the early station configuration with electrical power, storage, propulsion, and navigation guidance, until a short time after the Russian service module Zvezda docked and was transferred control. Zvezda contains the ESA built DMS-R Data Management System. Now primarily used for storage, Zarya provides ports for Soyuz spacecraft, Progress spacecraft and the European ATV to dock to the station. Ships boosting the station's orbit dock to the aft port (the rear port according to the station's normal orientation and direction of travel). The FGB is a descendant of the TKS spacecraft designed for the Russian Salyut program. 5.4 tons of propellant fuel can be stored and transferred automatically to and from ships docked. Zarya was originally intended as a module for the Russian Mir space station, but was not flown as of the end of the Mir-1 program. Developed by Russia and the former Soviet Union, construction of Zarya was funded by the United States and NASA, and Zarya remains a US-owned module.
The second module, Zvezda, is the station's Service Module - it provides a living environment for the crew, contains the ISS's main engine system, and provides a docking port for Soyuz, Progress and Automated Transfer Vehicle spacecraft.
The third module, Pirs, functions as the ROS's airlock, storing EVA spacesuits and providing the equipment necessary for cosmonauts to exit the space station. It also serves as a docking compartment for Soyuz and Progress spacecraft.
The fourth module, Poisk, is similar to Pirs. Redundancy in airlocks allows one airlock to be repaired internally and externally whilst crew use the other airlock to exit and re-enter the station.
The fifth module, Rassvet, is primarily used for cargo storage and as a docking port for visiting spacecraft.
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 which will take the place of Pirs. In October 2011, it was reported that Nauka was expected to be launched in December 2013. Prior to the arrival of the MLM, a Progress robotic spacecraft will dock with PIRS, depart with that module, and both will be discarded and burn up in the atmosphere. Nauka will then use its own engines to attach itself to the ROS. This module will be separated from the ISS before de-orbit with support modules and become the OPSEK space station. It contains an additional set of life support systems and orientation control. Power provided by its solar arrays will mean the ROS no longer relies on power from the USOS main arrays. Nauka's mission has changed over time. During the mid-1990s, it was intended as a backup for the FGB, and later as a universal docking module (UDM). Its docking ports will be able to support automatic docking of both space craft, additional modules and fuel transfer.
The Oka-T-MKS is a planned companion module to the ISS, which is as of December 2012 under construction. The module will be free-floating most of the time as an autonomous orbital space laboratory for the conduction of experiments, and dock with the ISS for experiment maintenance about every 180 days. The Oka-T-MKS space laboratory was contracted to Energia by Roscosmos in 2012. Originally projected for a 2015 launch date, this has been pushed back by a couple of years.
On June 17, 2009, the Russian Federal Space Agency (Roskosmos) presented to NASA and the other ISS partners a proposal to add additional modules to the Russian segment to ensure its viability past 2016 or even 2020. To this end, a Nodal Module that would be attached to the nadir docking port of the MLM Nauka would facilitate the attachment of two additional, larger modules that would be capable of providing an independent power source to the Russian segment should current plans to deorbit the US segment of the ISS after 2016 move forward. As proposed, the Nodal Module would be launched during 2013 by a Soyuz launcher in a similar fashion to how the Pirs and Poisk MRM-2 modules were lifted to orbit. The two larger modules, nominally referred to as Scientific and Power Producing Modules 1 and 2, would be lifted to orbit via Proton launchers in 2014 and 2015, respectively. These two modules would be attached to the port and starboard sides of the Nodal Module, leaving its aft docking port accessible for possible future expandability and its nadir port accessible for docking by Soyuz or Progress spacecraft. Because of the proximity of the Nodal Module to the planned attachment point of MRM-1 on the nadir docking port of Zarya FGB to facilitate docking of Soyuz and Progress spacecraft, the module's forward-facing port will be unusable. As of January 2010, neither Roskosmos nor NASA have provided further details of these modules or verification that they have been officially funded by the Russian government or added to the ISS launch manifest schedule. 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 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 will be equipped with an active hybrid docking port, which enables docking with the MLM module. The remaining five ports would be passive hybrids, enabling docking of Soyuz and Progress vehicles, as well as heavier modules and future spacecraft with modified docking systems. However more importantly, the node module was conceived to serve as the only permanent element of the future Russian successor to the ISS, 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. This would be a progression beyond the ISS and Russia's modular MIR space station, which are in turn more advanced than early monolithic first generation stations such as Skylab, and early Salyut and Almaz stations.