Russian Orbital Segment

[1] The segment currently consists of six modules, which together essentially comprise the base configuration of the cancelled Russian space station Mir-2.

[3] Now primarily used for storage, Zarya provides ports for Soyuz and Progress spacecraft and the European ATV to dock to the station.

Zarya was originally intended as a module for the Russian Mir space station,[citation needed] but was not flown as of the end of the Mir-1 program.

The fifth module to be launched, Rassvet, is primarily used for cargo storage and as a docking port for visiting spacecraft.

A backup flight article for FGB-based Zarya, known in production as FGB-2, was originally planned to serve as the Universal Docking Module, though its construction had been halted at 70% completion in the late 1990s.

It functioned as the ROS's airlock, storing EVA spacesuits and providing the equipment necessary for cosmonauts to exit the space station.

As of January  2021[update], neither Roscosmos 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.