Russia’s Aerospace Forces launched a Soyuz-2-1b rocket Friday, carrying a satellite designed to give the Kremlin advance warning of missile attacks. Soyuz lifted off from the Plesetsk Cosmodrome at about 10:46 Moscow Time (07:46 UTC), beginning a multi-hour mission to deliver the Tundra No.4 satellite into an elliptical Molniya orbit.
Friday’s launch carried the fourth Tundra satellite into orbit. Tundra spacecraft, which form part of Russia’s Kupol missile detection system, monitor the Earth Do from their high vantage points watching for signs of missile launches below. Kupol, which was previously known as Edinaya Kosmicheskaya Sistema (EKS) – meaning Unified Space System – is a replacement for the Soviet-era Oko system that stood watch during the Cold War.
The Tundra satellite was built by RKK Energia, based around the Viktoria platform that the company developed with its previous experience constructing Yamal communications satellites in the late 1990s. Tundra incorporates an infrared telescope to detect heat sources – such as the exhaust from missile launches – with complementary optical and ultraviolet sensors also installed. Using this suite of instruments, the missile can be tracked throughout its flight, allowing its potential targets to be identified more quickly than with ground-based radar tracking.
In addition to its missile detection payload, each Tundra spacecraft is also equipped with an emergency communications payload that could be used to send orders to strategic missile bases in the event of a nuclear war.
Tundra satellites operate in Molniya orbit – a class of highly-elliptical orbit that allows them to spend most of their time over the northern hemisphere. Molniya orbits, whose name comes from the Russian word for lightning, were first used in the 1960s by their namesake series of Soviet communications satellites.
A Molniya orbit is inclined at about 63.4 degrees to the equator. This inclination not only ensures that the satellite passes over far northern latitudes of the Earth’s surface, but it also reduces to near zero perturbations that would cause the argument of perigee to change over time. Combining the 63.4-degree inclination with an argument of perigee between 270 and 360 degrees, the apogee of the orbit – the point farthest from Earth – is frozen over the Northern hemisphere. An orbital period of just under 12 hours allows two full revolutions to be completed per day – so the satellite always reaches apogee over the same two points on the Earth’s surface every day.
For missile detection satellites like Tundra, the Molniya orbit allows a small constellation of satellites to provide continuous coverage of critical regions from where missile attacks could originate, including North America as well as the North Atlantic and Pacific Oceans, from where submarine-launched ballistic missiles could be fired. These orbits also allow coverage of the Arctic – the shortest route between missile bases in the United States and many of their likely targets in Russia – which would not be possible if the satellites were operated in geostationary orbit.
As well as the Tundra satellites, the Kupol system includes a ground segment, with the main control center located in the military town of Serpukhov-15 near Moscow.
Russia and the United States both maintain constellations of early-warning satellites to alert their respective governments and militaries of potential incoming missile threats. The US equivalent to Kupol is the Space-Based Infrared System (SBIRS) operated by the US Space Force. Unlike Kupol, SBIRS primarily uses geostationary satellites which can continuously observe a full disc of the Earth from a fixed position relative to the surface. Additional sensors piggybacked on National Reconnaissance Office (NRO) satellites in Molniya orbits are used to observe the far northern regions that are out of sight of the geostationary spacecraft.
Now that Tundra No.4 has reached orbit, it will be assigned a new name under the Kosmos series that Russia uses to refer to its military satellites publicly. Kosmos designations are assigned sequentially, beginning with the Kosmos 1 satellite launched in March 1962. In the early days of the space race the designations were also applied to prototypes in the Soviet human spaceflight and planetary exploration programs and to interplanetary probes that failed to leave Earth orbit. However, in recent years the designations have been applied exclusively to military spacecraft. Tundra No.4 is expected to become Kosmos 2546.
Friday’s Tundra launch was carried out by a Soyuz-2-1b rocket with a Fregat upper stage. Soyuz-2-1b is one of three versions of the Soyuz-2 rocket, the current generation in a series of rockets that date back to the dawn of the space age. Soyuz is a descendent of Sergei Korolev’s R-7 missile – the world’s first intercontinental ballistic missile – which first flew in May 1957 and was used to deploy the first satellite, Sputnik, five months later.
The R-7 was a two-stage missile, but to make it more suited to satellite launches several versions with additional stages were developed – initially the three-stage Vostok and four-stage Molniya. A more powerful three-stage version, Voskhod, was introduced in 1964 incorporating the third stage of the Molniya. Soyuz began life as an enhanced version of Voskhod, designed to carry the Soyuz spacecraft then under development for human spaceflight missions. Soyuz first flew in November 1966.
Early Soyuz rockets were used exclusively in support of the Soyuz spacecraft. However, in 1973 the Soyuz-U variant was introduced, designed as a universal replacement for a myriad of different versions of the R-7 then flying. Soyuz-U would go on to become the most-launched orbital carrier rocket in history, making over 780 flights and only retiring in 2017. Two variants – the Soyuz-U2 which used synthetic kerosene propellant to gain additional performance, and the Soyuz-FG which incorporated upgraded engines, were also flown.
Soyuz-2 was developed as a modernized replacement for the Soyuz-U and Soyuz-FG rockets and was the first version of Soyuz to incorporate digital flight control systems. First flying in 2004, the rocket also featured improved engines on its first and second stages. The addition of an optional Fregat upper stage – which had previously been tested on four Soyuz-U launches and then used on a number of Soyuz-FG missions – allowed higher orbits to be reached and more complex missions performed than with the three-stage Soyuz alone. This capability meant that Soyuz-2 could also replace the only other surviving member of the R-7 family, the Molniya-M, which made its last flight in 2010.
Three different versions of the Soyuz-2 have been developed, with different levels of performance for different types of mission. The Soyuz-2-1a was the first version of Soyuz-2 to fly, and aside from the avionics and engine upgrades is fairly similar to the earlier Soyuz-U, with its third stage powered by and RD-0110 engine. Soyuz-2-1b, which was used for Friday’s launch, also incorporates a redesigned third stage with an RD-0124 engine. The Soyuz-2-1v is a smaller rocket consisting of the second and third stages of a Soyuz-2-1b – the former re-engined with an NK-33 powerplant – without the four boosters that make up the iconic first stage of a traditional Soyuz rocket.
Soyuz launches can take place from five operational launch pads at four different launch sites. These include the Baikonur Cosmodrome in Kazakhstan, the Vostochny Cosmodrome in eastern Russia and the Centre Spatial Guyanais in Kourou, French Guiana. Two pads are located at Site 43 of the Plesetsk Cosmodrome in Northern Russia, from where Friday’s launch took place. Site 43 was originally built to support operational R-7A missile deployments in the early 1960s, serving in this role until the R-7A was declared obsolete in 1968, and taking on its new role as an orbital launch complex in 1969.
The two pads at Site 43 – designated 43/3 and 43/4 were initially used by Vostok-2M, Voskhod and Molniya-M rockets, with the first Soyuz launch from the complex being the maiden flight of the Soyuz-U in 1973 from Pad 3.
Work to convert Pad 4 for Soyuz-2 launches began in 2001, with the facility entering three years of maintenance downtime. In October 2002 a Soyuz-U failed on liftoff from Pad 3 and debris fell back onto the launch pad, taking it out of use pending repair. Although Pad 4 was brought back into service in 2004 with the first Soyuz-2-1a launch, Pad 3 would not see another launch until December 2019.
Soyuz rockets are assembled horizontally in a hangar – or MIK – and transported to the pad by rail. Once at the pad, Soyuz was raised to vertical and the pad’s four hold-down arms, its umbilical towers and the two halves of the service tower were raised into position around the rocket.
The first and second stages of Soyuz burned simultaneously. The first stage consisted of four boosters, clustered around the central second stage, or Blok-A. Each of the boosters – designated Blok-B, V, G and D – was powered by a single RD-107A engine while the second stage had an RD-108A. These engines were nearly identical – each burning RG-1 kerosene propellant and liquid oxygen in four combustion chambers – but the RD-108A also included four vernier nozzles, which provided attitude control during the climb towards orbit.
The startup sequence began about sixteen seconds before liftoff with the first and second stage engines igniting at their preliminary thrust levels. These were slowly brought up to full thrust as the countdown ticked towards zero, when the launch pad’s arms swung open and Soyuz began its ascent.
For the first 118 seconds of the flight the combined five engines on the first and second stages burned to power Soyuz away from the launch pad. Once the first stage exhausted its propellant it separated, with residual oxygen being vented through the nose of each booster to push it away from the second stage. The four boosters separating from the core of the rocket creates the distinctive Korolev Cross in the sky, named after the rocket’s designer.
After first stage separation, the second stage continued to burn its RD-108A engine for another 170 seconds before the rocket’s third stage took over. The separation of the second stage from the third was a “fire-in-the-hole” staging event, where the third stage ignited before second stage shutdown or separation had occurred. A lattice interstage structure at the top of the second stage allowed exhaust gasses from the third stage to escape safely. This type of separation is normal for Soyuz, as it keeps propellant settled in the third stage tanks without the need for additional ullage motors. A few seconds after the stages separated the third stage’s aft skirt was also jettisoned, splitting into three sections.
Like the first two stages, the third stage of Soyuz-2-1b burned RG-1 propellant and liquid oxygen. Its RD-0124 engine fired for around four and a half minutes before deploying Fregat to carry the Tundra satellite the rest of the way to orbit. Shortly after separating from the third stage, Fregat ignited its S5.98M engine for its first burn, setting up an initial parking orbit.
Fregat, which used storable propellant – unsymmetrical dimethylhydrazine (UDMH) and dinitrogen tetroxide – can restart its engine multiple times in flight allowing complex missions to be performed. To reach Molniya orbit and deploy Tundra No.4, it would have likely made two more burns – for a total of three – over a period of several hours after launch. Following the completion of Fregat’s last burn, Tundra separated from the upper stage.
Friday’s launch was Russia’s first since 25 April, when a Soyuz-2-1a sent the Progress MS-14 cargo craft on its mission to the International Space Station, and the country’s first military launch since March. With space and satellite programs currently disrupted by the worldwide medical situation, Russia’s next orbital launch is not likely to occur until July. A military Soyuz-2-1b launch with a navigation satellite to upgrade the GLONASS constellation is expected around the middle of the month, with another Progress launch to the space station slated for 23 July.
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