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Image Credit: Roscosmos.

Arianespace to launch ninth mission for OneWeb

[UPDATED] A Russian Soyuz 2.1b rocket is scheduled to blast off from the Baikonur Cosmodrome in Kazakhstan on Saturday evening, August 21, 2021 at 22:13 UTC / Sunday morning, August 22 at 03:13 QYZT (local time). The four-stage, liquid-fueled, medium-lift launch vehicle will carry the next 34 satellites for OneWeb’s high-speed Internet broadcasting satellite constellation into a low Earth orbit.

The mission, which is managed by Arianespace, Starsem and Roscosmos, was originally scheduled to launch on August 19 at 22:23 UTC, but had to be postponed to no earlier than Friday, due to an off-nominal event. On Friday evening, Arianespace announced to postpone the launch another 24 hours to allow for additional time for mission planning.

The OneWeb satellites

Soyuz will launch 34 satellites for OneWeb’s high-speed Internet broadcasting satellite constellation into a 450 km high and 84.7 degrees inclined low Earth orbit. The spacecraft will join the 254 previously launched satellites, increasing the number of crafts the constellations is made of to 288.

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

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

The Soyuz launch vehicle

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 active service, had its maiden flight in 2004 from the Plesetsk Cosmodrome in Russia.

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

The first stage is comprised of four liquid oxygen (LOX) / RP-1 fueled strap-on 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 one launch.

A Soyuz rocket blasts off from the Vostochny Cosmodrome, carrying 36 OneWeb satellites. Image Credit: Roscosmos.
A Soyuz rocket blasts off from the Vostochny Cosmodrome, carrying 36 OneWeb satellites. Image Credit: 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 will ignite, lifting the launch vehicle off the pad and toward low Earth orbit.

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

Almost five minutes into the flight, the Blok-A will run out of propellant and separates from the Blok-I third stage, which will then continue to push the 34 satellites toward their target orbits.

Shortly after the ignition of the Blok-I, the two payload fairing halves will be jettisoned from the rocket, exposing the Fregat upper stage and the payload to the vacuum of space.

9 ½ minutes after liftoff, the rocket’s third stage will separate from the Fregat upper stage, which will then coast for about a minute, before igniting its engine for around four minutes. After cut off of the NTO / UDMH fueled stage, the Soyuz will enter a second coast phase, lasting one hour and eight minutes.

At T+1 hour and 6 minutes, the Fregat will ignite its S5.92 engine for a second time, to insert the payloads into their target orbits. This will be followed by the separation of the first two OneWeb satellites from their dispenser.

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

The final four spacecraft are expected to be deployed from the dispenser 3 hours and 45 minutes after the launch at the Baikonur Cosmodrome in Kazakhstan.

Once the satellites are deployed from the rocket, they will use their own onboard propulsion system to raise their transfer orbit and to position themself into their operational orbits.


Sources:

https://www.arianespace.com/press-release/flight-st34-postponement-of-the-launch/

https://www.arianespace.com/press-release/flight-st34-postponed-24-hours/

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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