# Baikonur Cosmodrome Site 31

45°59′46″N 63°33′51″E﻿ / ﻿45.99611°N 63.56417°E﻿ / 45.99611; 63.56417
Baikonur Site 31, also designated as Site 31/6, is a launch complex at the Baikonur Cosmodrome in Kazakhstan. It serves as a key launch site, supporting Soyuz-2 launches for both crewed and uncrewed missions. The site was first utilized on 14 January 1961 for a test flight of the R-7A, an intercontinental ballistic missile on which the Soyuz rocket family was based. Since 2020, following Roscosmos' transition from the Soyuz-FG to the Soyuz-2 rocket for crewed missions, Site 31 has become the primary launch site for Soyuz flights to the International Space Station (ISS). This shift occurred after Site 1/5, also known as Gagarin's Start, failed to secure funding for upgrades to accommodate the slightly larger Soyuz-2 rocket. Before that, it only saw a handful of crewed flights when Site 1/5 was unavailable.

## History

Construction of Site 31/6 at Baikonur began in late 1958 as a second launch complex for the R-7 intercontinental ballistic missile (ICBM) at the cosmodrome. The numbering of the sites reflected Baikonur’s role as a secondary ICBM base, with the primary being the Plesetsk Cosmodrome, which featured four launch complexes. While Site 1/5 was primarily a test facility, Site 31 was designed as an operational "battle station" for the R-7, equipped with specialized infrastructure. This included an assembly building, a processing facility for nuclear warheads, a diesel-powered energy plant, and a nearby residential complex. Drawing on the experience gained during the construction of Site 1, engineers made several design improvements for Site 31. The flame trench was scaled down, and assembly and support facilities were closer to the launch pad to improve efficiency and streamline operations. Construction was completed by the end of 1960, and the first R-7 ICBM successfully launched from Site 31/6 on 27 February 1961.
As the R-7's role as a nuclear delivery system diminished, Site 31 was repurposed to support orbital launches, including those carrying cosmonauts. The facility’s design allowed access to orbits with four different inclinations. By 1966, a dedicated fueling station had been established to support piloted spacecraft and satellite operations. The site played a key role in preparing early Soyuz spacecraft, including the original Soyuz 7K-OK and the circumlunar 7K-L1 vehicles. The facility experienced a devastating on-pad explosion in December 1966 that claimed three lives during the Soyuz 7K-OK No.1 mission. It resumed operations in January 1969, launching the Soyuz 4 mission and supporting numerous missions throughout the 1970s. Following the explosion of Soyuz 7K-ST No.16L at Site 1 in 1983, Site 31 became critical for crewed missions, launching Soyuz T-10, T-11, and T-12 in 1984. Even after the repairs were completed, Site 31 remained an important backup to Site 1, hosting 12 of the 100 Russian crewed launches by 2006.
In 2005, it was reported that Site 31 was selected to receive significant upgrades to accommodate the larger, modernized Soyuz-2 rocket and to support an anticipated demand for flights to the International Space Station with the impending retirement of the Space Shuttle. These upgrades were completed between 2007 and 2008, and improvements included an overhauled fueling system, a modernized flight control bunker, and air-conditioning and communications systems to support payload integration. These updates enabled the resumption of launches from Site 31 in 2009, with Progress M-66 marking the first cargo mission that year, followed by Progress M-07M in 2010 and Progress M-15M in 2012. In 2012, piloted launches formally resumed with the successful liftoff of Soyuz TMA-06M, following the completion of further refurbishments. While Roscosmos had originally planned to upgrade Site 1 to support Soyuz-2 launches, that plan was eventually canceled.