A second docking compartment, Stykovochniy Otsek 2, was planned with the same design. However, when the Russian segment of the ISS was redesigned in 2001, the new design no longer included the SO-2, and its construction was canceled. After another change of plans the SO-2 module finally evolved into the Poisk module, which was added to the ISS in 2009.
The docking compartment has two primary functions: provide a docking port for visiting Soyuz and Progress spacecraft and serve as an airlock for Russian EVAs. The docking port can accommodate one Soyuz-TMA or one Progress-M spacecraft. Visiting spacecraft can deliver people and cargo to and from to the space station. In addition, the Docking Compartment can transfer fuel from the fuel tanks of a docked Progress resupply vehicle to either the Zvezda Service Module Integrated Propulsion System or the ZaryaFunctional Cargo Block. It can also transfer propellant from Zvezda and Zarya to the propulsion system of docked vehicles—Soyuz and Progress. The two airlocks are used for spacewalks by cosmonauts wearing Russian Orlan-M spacesuits. The Pirs docking compartment was manufactured by RKK Energia. The Docking Compartment is similar to the Mir Docking Module used on the Mir space station. The docking compartment's planned lifetime as part of the station was five years.
Launch
Pirs was launched on 14 September 2001, as ISS Assembly Mission 4R, on a Russian Soyuz-U rocket, using a modified Progress spacecraft, Progress DC-1, as an upper stage. The 3580 kilogram Pirs Docking Compartment is attached to the nadir port of the Zvezda service module. It docked to the InternationalSpace Station on 16 September 2001, and was configured during three spacewalks by the Expedition 3 crew. Two Strela cargo cranes were later added by the STS-96 and STS-101 missions, carried up on Integrated Cargo Carriers and installed during EVAs.
Future
Pirs was originally scheduled to be detached from the nadir port of the Zvezda module in 2013 to make room for the Russian Multipurpose Laboratory ModuleNauka. This has been delayed first to 2017 and then to 2018 due to a series of launch failures with the Proton rocket leading to delays in the launch of Nauka. Current ISS flight manifest, drafted in early Summer 2020, has the Progress MS-15 mission extending to 274 days. Progress MS-15 would perform the planned deorbiting of the Pirs module on or around April 23, 2021. Pirs could become the first permanent ISS module to be decommissioned, and would be destroyed during atmospheric re-entry.
