Soyuz-FG


The Soyuz-FG was an improved variant of the Soyuz-U launch vehicle from the R-7 rocket family, developed by the Progress Rocket Space Centre in Samara, Russia. It featured upgraded first and second stage engines, RD-107A and RD-108A, respectively, with enhanced injector heads that improved combustion efficiency and specific impulse. The designation "FG" refers to forsunochnaya golovka in Russian.
Soyuz-FG made its maiden flight on 20 May 2001, delivering a Progress cargo spacecraft to the International Space Station. It became the primary vehicle for launching crewed Soyuz TMA, Soyuz TMA-M, and Soyuz MS spacecraft from 2002 until its retirement in 2019.
Launches occurred from the Baikonur Cosmodrome in Kazakhstan: crewed missions from Gagarin's Start and satellite launches from Site 31/6.

Design

Soyuz-FG was introduced in May 2001 as a transitional solution while the more advanced Soyuz-2 was still in development. Development of the upgraded RD-107A and RD-108A engines outpaced the rest of the Soyuz-2 rocket. The availability of the upgraded engines allowed their early use on Soyuz-FG, while Soyuz-U continued using existing engine stockpiles.
The RD-107A and RD-108A engines, replaced the older RD-107 and RD-108 units, switching from 260 two-component centrifugal injectors to over 1,000 one-component injectors. This refinement enabled more complete propellant combustion, reduced high-frequency vibrations in combustion chambers, and improved specific impulse by, a five percent improvement, which allowed for a payload increase of.
For uncrewed missions, Soyuz-FG could fly with a Fregat upper stage, built by Lavochkin in Khimki. The first flight of this configuration took place on 2 June 2003, with a total of ten such launches marketed by the European-Russian company Starsem.
Soyuz-FG flew 70 times, with one failure on 11 October 2018 during the launch of Soyuz MS-10. A faulty sensor led to a booster collision with the core stage shortly after liftoff, triggering an emergency abort. The crew—NASA astronaut Nick Hague and Russian cosmonaut Aleksey Ovchinin—safely returned to Earth.
Following the MS-15 launch on 25 September 2019, Soyuz-FG was retired in favor of the fully digital Soyuz-2, which offers more precise guidance and greater mission flexibility.