Pirs (, meaning "pier") – also called Stykovochny Otsek 1 (SO-1; , "docking module") and DC-1 (Docking Compartment 1) – was a Russian module on the International Space Station (ISS). Pirs was launched on 14 September 2001, and was located on the Zvezda module of the station. It provided the ISS with one docking port for Soyuz and Progress spacecraft, and allowed egress and ingress for spacewalks by cosmonauts using Russian Orlan space suits. Pirs was docked to Zvezda for almost 20 years, until 26 July 2021, where it was decommissioned and undocked by Progress MS-16 to make way for the new Nauka module. Poisk module A second docking compartment, Stykovochniy Otsek 2 (SO-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. Design and construction The docking compartment had two primary functions: provide a docking port for visiting Soyuz and Progress spacecraft and serve as an airlock for Russian EVAs. The docking port could accommodate one Soyuz-MS or one Progress-MS spacecraft. Visiting spacecraft could deliver people and cargo to and from to the space station. In addition, the Docking Compartment could transfer fuel from the fuel tanks of a docked Progress resupply vehicle to either the Zvezda Service Module Integrated Propulsion System or the Zarya Functional Cargo Block. It could also transfer propellant from Zvezda and Zarya to the propulsion system of docked vehicles — Soyuz and Progress. The two airlocks were used for spacewalks by cosmonauts wearing Russian Orlan-M spacesuits. The Pirs docking compartment was manufactured by RKK Energia. The Docking Compartment was 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 launch vehicle, using a modified Progress spacecraft, Progress DC-1, as an upper stage. The Pirs Docking Compartment was attached to the nadir (bottom, Earth-facing) port of the Zvezda service module. Docking Pirs docked to the International Space Station on 17 September 2001, at 01:05 UTC, and was configured during three spacewalks by the Expedition 3 crew. Two Strela cargo