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Image Credit: Vostochny Space Center / Roscosmos.

Soyuz launches the next 36 OneWeb satellites

A Soyuz 2.1b/Fregat rocket earlier today successfully blasted off from the Vostochny Cosmodrome in Russia, carrying the next 36 spacecraft for OneWeb’s satellite constellation into a low Earth orbit.

Launch of the four-stage, medium-lift launch vehicle occurred at 09:40 UTC / 18:40 YAKT from Site 1 at the Vostochny Cosmodrome in the Far East of Russia.

The mission, designated “ST-36”, was managed by Arianespace, Starsem and Roscosmos and was the seventh OneWeb mission launched in 2021. Over half of the 650 planned satellites have now been placed into an orbit around planet Earth.

Soyuz and its payload blast off from the Vostochny Cosmodrome in Russia. Image Credit: Vostochny Space Center / Roscosmos.
Soyuz and its payload blast off from the Vostochny Cosmodrome in Russia. Image Credit: Vostochny Space Center / Roscosmos.

The OneWeb satellites

The Soyuz rocket launched a total of 36 satellites for OneWeb’s satellite constellation into a 450 km high and 84.7 degrees inclined low Earth orbit. Once the spacecraft have reached their operational orbits, they will join the 322 previously launched satellites, increasing the number of crafts the constellations is made of to 358.

Once all 650 satellites are placed into orbit, OneWeb plans to provide high-speed, low-latency Internet access to every place on the planet.

The company expects to begin commercial services in the UK, Alaska, Canada, Northern Europe, Greenland, Iceland and the Arctic Sea by the end of 2021.

The 36 OneWeb satellites launched seen during integration atop the Fregat upper stage. Image Credit: Vostochny Space Center / Roscosmos.
The 36 OneWeb satellites launched seen during integration atop the Fregat upper stage. Image Credit: Vostochny Space Center / Roscosmos.

The Soyuz rocket

The Soyuz rocket is a Russian launch vehicle derived from the Vostok rocket, the launch vehicle used to launch Yuri Gagarin, the first human to fly to space.

The Soyuz first flew in 1966 and has since conducted over 1,900 crewed and uncrewed launches, making the vehicle the most frequently flown rocket ever developed.

The rocket is launched from four different spaceports in three countries on three continents and is capable of carrying over eight tonnes into a low Earth orbit, or over three tonnes into a geostationary transfer orbit.

The Soyuz 2, the modernized version of the Soyuz currently in service, had its maiden flight in 2004 from the Plesetsk Cosmodrome in Russia.

The Soyuz 2.1b/Fregat, the configuration used to launch today’s OneWeb mission, is a four-stage, liquid-fueled, medium-lift launch vehicle.

The first stage is comprised of four liquid oxygen (LOX) / RP-1 fueled boosters, known as Blok-B, V, G and D. Each booster is 19.6 m in length, up to 2.68 m in diameter and is equipped with a single four-chamber RD-107A rocket engine, providing over 800 kN of thrust at sea level.

The four boosters are attached to the Blok-A core stage, which has a length of 27.10 m, a diameter of up to 2.95 m and a launch mass of almost 100 tonnes. The Blok-A is powered by a four-chamber RD-108A rocket engine, burning liquid oxygen and RP-1 as propellants. The stage has a burn time of over 280 s and provides almost 800 kN of thrust.

The rocket’s third stage, known as the Blok-I, is 6.70 m tall, has a diameter of 2.66 m and a launch mass of about 28 tonnes. It also utilized LOX and RP-1 as propellants and provides around 300 kN of thrust in vacuum.

The final stage, the Fregat, is a 3.35 m wide and 1.50 m tall space tug, equipped with a single S5.92 liquid rocket engine, burning dinitrogen tetroxide (NTO) and unsymmetrical dimethylhydrazine (UDMH) as propellants. The Fregat is able to reignite its engine multiple times, making it possible to launch several satellites into different orbits in a single launch.

Launch of the Soyuz 2.1b/Fregat rocket from the Vostochny Cosmodrome. Image Credit: Vostochny Space Center / Roscosmos.
Launch of the Soyuz 2.1b/Fregat rocket from the Vostochny Cosmodrome. Image Credit: Vostochny Space Center / Roscosmos.

Mission profile

At T 0, the four RD-107A rocket engines of the Soyuz’s four boosters and the single RD-108A engine of the rocket’s core stage ignited, lifting the launch vehicle off the pad and toward low Earth orbit.

About two minutes after launch, propellant levels in the four boosters depleted and they were jettisoned from the Blok-A core stage.

At T+3 min 35 s, the two payload fairing halves were jettisoned from the rocket, exposing the Fregat upper stage and the payloads to the vacuum of space.

Almost five minutes into the flight, the Blok-A run out of propellant and separated from the Blok-I third stage, which then continued to propel the 36 satellites toward their target orbit.

9 ½ minutes after liftoff, the rocket’s third stage separated from the Fregat upper stage, which then coasted for about a minute, before igniting its engine for around four minutes. After cut off of the NTO / UDMH fueled stage, the Soyuz enterd a second coast phase.

At T+1 hour and 13 minutes, the Fregat reignited its S5.92 engine for a second time, to insert the payloads into their target orbit. That was followed by the separation of the first four OneWeb satellites from their dispenser.

Over the next ~2 ½ hours, the Fregat firedg its ACS (Attitude Control System) thrusters eight times, to properly orientate the stage ahead of the satellites’ separations. Each burn was followed by the separation of four more satellites.

The final four spacecraft were deployed from the dispenser 3 hours and 51 minutes after the launch at the Vostochny Cosmodrome, bringing an end to the launch vehicle’s mission.

Over the next couple of weeks, the 36 spacecraft will use their own onboard propulsion system to position themself into their final operational orbits.


Sources:

https://www.arianespace.com/press-release/soyuz-st36-oneweb-success/

http://en.roscosmos.ru/22423/

https://www.arianespace.com/wp-content/uploads/2015/09/Soyuz-Users-Manual-March-2012.pdf

https://www.arianespace.com/wp-content/uploads/2021/05/ST32-launchkit-EN2.pdf

https://www.arianespace.com/wp-content/uploads/2020/03/ST28-launch-kit_EN2.pdf

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