Soyuz-FG's long road to retirement
The 21st century version of the legendary Russian Soyuz rocket family, which carries cosmonauts into orbit, has the designation Soyuz-FG, where "FG" stands for "forsunochnaya golovka" -- Russian for the injector head. It was the main component which had gotten a makeover when the Soyuz-FG variant was introduced in 2001. Despite much more significant improvements in the works, the Soyuz-FG's working career then span over nearly two decades.
General architecture of the Soyuz-FG rocket
Soyuz-FG: A small step forward
The Soyuz-FG represented the fifth round of gradual upgrades since the end of the 1950s in what is known today as the Soyuz rocket family. The focus of the FG program were the main engines on the four boosters of the first stage and on the core booster of the second stage.
In development since around 1993, the new injector heads were designed to improve the mixing of fuel and oxidizer sprayed inside the combustion chambers of the modified RD-107A (14D22) and RD-108A (14D21) engines which propel the first and second stage, respectively. The older RD-107 (11D512) and RD-108 (11D511) engines used 260 two-component centrifugal injectors, while the new engines received more than 1,000 one-component injectors. They allowed finer aeration of propellant for more thorough burning of its components while also reducing the probability of high-frequency vibrations inside the combustion chambers. (813)
Because RD-107 and RD-108A were successfully tested and ready for flight ahead of other upgrades planned for the Soyuz-2 series of rockets, the developers decided to introduce an intermediate version of the rocket designated Soyuz-FG (11A511U-FG), which would feature the modified engines on the first and second stage. (814)
This relatively small upgrade increased the specific impulse of the engine by around five seconds or by 1.3 percent. As a result, Soyuz-FG could carry from 250 to 300 kilograms of extra payload to a 200-kilometer orbit when compared to that of the Soyuz-U variant. When launched with the manned Soyuz transport spacecraft (its main payload), Soyuz-FG could deliver up to 7,200 kilograms in the low Earth's orbit. The Soyuz-FG could also carry the 7,400-kilogram Progress cargo ship.
All other components of the Soyuz-FG were borrowed largely unchanged from the Soyuz-U variant, which also remained in operation. As its older siblings, the Soyuz-FG was equipped with a flight control system developed at the SKB Polisvit design bureau and serially produced at the Kommunar factory. Both organizations were based in the city of Khrakov, Ukraine.
A typical flight profile
According to a generic flight profile, the Soyuz-FG drops its four boosters of the first stage 118 seconds after liftoff, while the second stage continues firing until 287 seconds in flight. Depending on the mission, the third stage inserts its payload into an initial Earth's orbit from 520 to 540 seconds after launch.
The payload fairing protecting the satellites during the ascent through the atmosphere can be dropped from 127 to 207 seconds into the flight at an altitude from 70 to 100 kilometers above the Earth's surface, when the rocket has a velocity from 1,800 to 2,200 meters per second. The exact parameters of the ascent timeline depend on the available drop zones for a given ascent trajectory. (120)
Long road to retirement
Like all previous launchers assigned to carry crews, the Soyuz-FG would have to be "man-rated" during test launches with unmanned satellites, before it could be entrusted with the life of cosmonauts. In the case of Soyuz-FG, its introduction was timed to precede the first mission of the Soyuz TMA spacecraft variant, which could take advantage of the launcher's extra cargo capacity.
On May 21, 2001, the first Soyuz-FG successfully launched the Progress M1-6 cargo ship, followed by two more flawless launches with Progress spacecraft in 2001 and 2002. On October 30, 2002, Soyuz-FG carried its first crew riding to orbit in the Soyuz TMA-1 spacecraft. The rocket has remained the sole carrier of manned vehicles ever since. By 2016, after 15 years in service, Soyuz-FG had made 48 launches with the manned Soyuz spacecraft and two missions with the Progress cargo ships within the ISS program and eight missions with commercial payloads.
Ironically, the Soyuz-FG was initially seen only as a stop-gap variant on the road to the Soyuz-2 series, which would incorporate the newest features of the Soyuz-FG, in addition to much more radical upgrades, including a new-generation flight control system.
However, the plans to switch human missions from the Soyuz-FG to the Soyuz-2, initiated as early as 2005, took years longer than planned.
As of 2012, the production of Soyuz-U-PVB and Soyuz-FG variants was expected to cease by the beginning of 2016. In 2014, the conflict with Ukraine, which supplied flight control avionics for Soyuz-U and Soyuz-FG, made the switch even more urgent. With the two former Soviet republics at a virtual state of war, NASA had to ask the US State Department to plead with the Ukrainian government to supply necessary hardware for Soyuz-FG and Soyuz-U-PVB. To make matters worse, in April 2015, the second attempt to launch a Progress cargo ship on a Soyuz-2-1a rocket resulted in a dangerous accident, which could have doomed a crew had it been onboard.
The Soyuz-2-1a test flight program resumed in December 2015, but the actual switch of human missions to Soyuz-2.1a was put off as far as 2019. According to NASA sources, soon after the Progress M-27M accident, top Roskosmos officials assured the head of the NASA Space Station Program Office Manager Michael T. Suffredini that they would not retire the old reliable Soyuz-FG for as long as the US space agency continues booking seats on the Soyuz spacecraft for its astronauts heading to the ISS. As of 2017, the most recent iteration of the NASA contract for Soyuz flights would end in 2019.
Not surprisingly, in March 2017, the official Russian press announced that human missions would be switched from Soyuz-FG to the Soyuz-2-1a rocket in 2019 or 2020. As of September 2017, the plan was to switch human missions to Soyuz by the beginning of 2019.
On Aug. 11, 2017, RKK Energia submitted an integrated schedule to Roskosmos to use the two remaining Soyuz-FG rockets for the launches of the Progress MS-10 (No. 440) cargo ship on Oct. 11, 2018, and that of the Progress MS-11 (No. 441) scheduled for Feb. 6, 2019.
These rockets were originally manufactured for the launches of the Soyuz MS-12 (No. 742) spacecraft in March 2019 and Soyuz MS-13 (No. 743) in September 2019.
On Aug. 30, 2017, Roskosmos gave a contract to RKTs Progress in Samara to conduct minor rework on the two Soyuz-FG rockets to adapt them for the Progress MS vehicles.
As of September 2017, the two final Soyuz-FG rockets had been scheduled to fly in April and September 2020. However the Roskosmos leadership was pressing the industry to retire the FG variant as early as 2019 to cut costs and avoid problems with Russian security services, which put serious obstacles in obtaining avionics and associated technical assistance from Ukraine's Kommunar plant. As a result, at least one of previously planned launches of Soyuz-FG in 2020 could be performed in 2019, industry sources said.
As of October 2018 (before the launch of Progress MS-10), a total of four Soyuz-FG rockets remained available and one was still undergoing assembly, industry sources said.
The final Soyuz-FG rocket launch Soyuz MS-15 spacecraft on September 25, 2019.
Soyuz-FG rocket with the Soyuz MS-13 spacecraft shortly before liftoff on July 20, 2019.
Specifications of the Soyuz-FG rocket:
Payload capabilities of the Soyuz-FG rocket as compared to Soyuz-U*:
Chronology of Soyuz-FG missions:
Soyuz-FG rocket launches European Mars Express probe on June 2, 2003. Credit: ESA
A Soyuz-FG rocket with the Soyuz TMA-17M spacecraft leaves assembly building at Site 112 on July 20, 2015. Click to enlarge. Credit: Roskosmos
Liftoff of Soyuz rocket. Click to enlarge. Credit: RKTs Progress
A demo version of the RD-107A engine. Click to enlarge. Copyright © 2010 Anatoly Zak
An adapter connecting Soyuz spacecraft to its Soyuz FG launch vehicle. Click to enlarge. Credit: Roskosmos
A Soyuz-FG rocket with the Soyuz-TMA-17 spacecraft shortly after its rollout to the launch pad in Baikonur on July 20, 2015. Click to enlarge. Credit: Roskosmos
A Soyuz-FG rocket lifts off with the Soyuz MS-05 spacecraft on July 28, 2017. Click to enlarge. Credit: NASA
Soyuz-FG launches Soyuz MS-07 on Dec. 17, 2017. Click to enlarge. Credit: Roskosmos
A long-exposure shot captures the ascent trajectory of the Soyuz-FG rocket with the Progress MS-10 spacecraft on Nov. 17, 2018. Click to enlarge. Credit: RKK Energia
Four boosters of the first stage and the escape rocket are seen separating during the launch of Soyuz MS-15 spacecraft on September 25, 2019. Credit: NASA