AKA: MRM 2;Poisk, Progress-M-SO 2;SO 1, Pirs, Progress-M-SO 1. Status: Operational 2001. Gross mass: 6,850 kg (15,100 lb). Height: 4.10 m (13.40 ft). Diameter: 2.60 m (8.50 ft).
The Stikovochniy Otsek No. 1 (SO1, Docking Module 1), article 240GK No.1L, was built by Energia and derived from Soyuz hardware. It had a mass of around 3900 kg and was a 4.1 m long, 2.6 m diameter ovoid. The SO1 was named Pirs (Russian for "pier") and was delivered to the station by Progress M-SO1 in a completely automatic rendezvous and docking operation. Pirs provided extra clearance from the Station for ships docking underneath Zvezda, and was used as an airlock for spacewalks using the Russian Orlan EVA suits.