There were two planned Russian element Docking Compartments (DCs) during the assembly sequence to provide egress/ingress capability for Russian-based EVAs and additional docking ports on the International Space Station. They are called "SO1" (Pirs) and "SO2". "SO1" (Pirs) was launched in August 2001 and "SO2" has been cancelled.

The Russian docking compartment was manufactured by RKK Energia. The Docking Compartment is similar to the ones used on the Mir space station. It provides docking ports for the Soyuz-TMA and Progress-M spacecraft. It also has an airlock to accomodate spacewalks by Russian cosmonauts wearing Orlan-M spacesuits.

The "SO1" Docking Compartment was delivered and attached to the International Space Station by special versions of the Progress-M supply spacecraft. The Docking Compartment has a mass of 3,630 kg.

The "SO1" (Pirs) is currently connected to the lower Service Module (Zvezda) docking port. It will be moved to the Science Power Platform, side docking port, above the ISS Zvezda module. This is scheduled to take place in 2009.

The "SO1" was scheduled to be discarded and reenter when the "SO2" is installed on the International Space Station.

The "SO2" has been cancelled and deleted due to lack of funding and the "S01" Pirs will continue to be used.

Pirs Docking Compartment — airlock specifications

• Length: 5 meters
• Diameter: 2.2 meters
• Weight: 3,630 kilograms
• Volume: 6 cubic meters

Sources

Some of the material in this article came from NASA [1].