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Image Credit: Yuzhny Space Center / Roscosmos.

Arianespace to launch their 1000th satellite Tuesday evening

Arianespace and Starsem are targeting Tuesday evening, September 14, 2021 at 18:07 UTC / 23:07 QYZT (local time) for the launch of a Russian Soyuz rocket from the Baikonur Cosmodrome in Kazakhstan. The mission, designated “ST35”, will orbit 34 additional spacecraft, including the 1000th satellite to be launched by Arianespace, for OneWeb’s low Earth orbit satellite constellation.

The flight will be the ninth rocket launch conducted by Arianespace in 2021 and the six Soyuz to be launched by the company this year.

Soyuz and the 34 OneWeb satellites at the launch pad in Baikonur. Image Credit: Yuzhny Space Center / Roscosmos.
Soyuz and the 34 OneWeb satellites at the launch pad in Baikonur. Image Credit: Yuzhny Space Center / Roscosmos.

The OneWeb spacecraft

The Soyuz rocket will launch a total of 34 satellites for OneWeb’s high-speed Internet broadcasting 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 288 previously launched satellites, increasing the number of crafts the constellations is made of to 322.

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

The Soyuz 2.1b/Fregat, the configuration used to launch the upcoming 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 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 a single launch.

A Soyuz blasts off from the Baikonur Cosmodrome, carrying 34 OneWeb satellites into orbit. Image Credit: Roscosmos.
A Soyuz blasts off from the Baikonur Cosmodrome, carrying 34 OneWeb satellites into orbit. 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 deplete and they will be jettisoned from the Blok-A core stage.

Almost five minutes into the flight, the Blok-A runs out of propellant and separates from the Blok-I third stage, which then continues to propel 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 separates 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 enters a second coast phase, lasting one hour and eight minutes.

At T+1 hour and 6 minutes, the Fregat reignites its S5.92 engine for a second time, to insert the payloads into their target orbit. 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 will be deployed from the dispenser 3 hours and 45 minutes after the launch at the Baikonur Cosmodrome, bringing an end to the launch vehicle’s mission.

Over the next couple of weeks, the 34 spacecraft will use their own onboard propulsion system to position themself into their final operational orbits.


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