OneWeb 4 | Soyuz 2.1b/Fregat

Lift Off Time
(Subject to change)
December 18, 2020 – 12:26:26 UTC | 15:26:26 MSK
Mission Name
OneWeb 4
Launch Provider
(What rocket company is launching it?)
Russian Federal Space Agency/Arianespace
Customer
(Who’s paying for this?)
OneWeb
Rocket
Soyuz 2.1b
Launch Location
Site 1S, Vostochny Cosmodrome, Russia
Payload mass
5,310 kg (~11,700 lbs)
Where are the satellites going?
Polar low-Earth orbit. Initial orbit of 450 km circular at 87.4°, final orbit of 1,200 km
Will they be attempting to recover the first stage?
No, this is not a capability of Soyuz
Will they be attempting to recover the fairings?
No, this is not a capability of Soyuz
Are these fairings new?
Yes
This will be the:
– 56th launch of Soyuz 2.1b
53rd Soyuz mission operated by Ariane Space
– 3rd operational launch of OneWeb satellites
– 1st OneWeb launch since filing for bankruptcy
Where to watch
Official livestream

What’s all this mean?

Arianespace is launching 34 OneWeb internet communication satellites on a Soyuz 2.1b rocket into a 1,200 km polar orbit. The rocket will take off from Vostochny Cosmodrome, in Russia. This launch will boost the number of OneWeb satellites launched to 108. OneWeb 4 will be OneWeb’s first launch since being acquired by the United Kingdom. The contract for this mission was revised in September, but is still part of the contract before OneWeb was acquired.

Despite Soyuz being a Russian rocket, the launch provider is still Arianespace. Ariane essentially subcontracts Roscosmos to launch a Soyuz on their behalf.

What is OneWeb?

OneWeb is a planned satellite internet constellation with the goal of providing internet coverage to the entire globe. Similar to SpaceX’s Starlink, the OneWeb constellation aims to deliver semilow-latency internet to locations where ground-based internet is unreliable or unavailable.

OneWeb plans to have 648 satellites in their constellation, providing them with the 600 satellites needed for global coverage and an additional 48 on-orbit spares incase a satellite fails. These satellites are in a 1,200 km low-Earth polar orbit, which is significantly lower than the global internet services available today, which orbit at 35,786 km above the Earth in geostationary orbit. However, the orbit of OneWeb’s satellites is still significantly higher than the 550 km orbit that SpaceX’s Starlink satellites are in. OneWeb is expecting the final 648 satellite constellation to provide download speeds of roughly 50 Mb/s.

Final orbits of the 648 satellite constellation (Credit: Airbus)

Due to the relatively low nature of this orbit, the OneWeb constellation’s primary goal is providing internet connectivity and communication.

The constellation consists of 18 orbital planes, with 36 satellites in each plane. However, in May of 2020 OneWeb submitted a permit application to increase their constellation size to 48,000 satellites.

What is a OneWeb satellite?

Each OneWeb satellite has a compact design and a mass of around 150 kg. The satellites are each equipped with a Ku-band antenna, operating between 12 and 18 GHz (.01665 and .02498 meters). One interesting note is that these satellites will use a slightly abnormal frequency, eliminating interference with satellites in geostationary orbit.

The OneWeb satellites were built by OneWeb satellites, which is a joint venture between OneWeb and Airbus.

The satellites are designed to safely deorbit after 25 years, however this leaves many concerned as this orbital region is already the most crowded with space debris.

Artist depiction of a OneWeb satellite (Credit: TechCrunch)

OneWeb’s return

In March of 2020 OneWeb filed for Chapter 11 bankruptcy and laid off most of their employees. However, OneWeb was able to maintain operations for the 74 satellites they current had in orbit. After the future of OneWeb was questionable for several months, in November of 2020 the UK government and Bharti Enterprises invested over a billion dollars into OneWeb with the current goal of finishing the constellation.

What is Soyuz 2.1b?

Introduced in 1966, the Soyuz rocket (also known as R7) has been the workhorse of the Soviet/Russian space program. The first launch of the Soyuz 2.1a version on November 8, 2004 from the Plesetsk Cosmodrome represented a major step in the Soyuz launch vehicle’s development program. Fregat is the upper (4th) stage of Soyuz 2.1, and it first flew in the year 2000.

Evolution of the R7 / Soyuz rocket family
Evolution of the R7 / Soyuz rocket family (Credit: NASA / Peter Gorin / Emmanuel Dissais)

The Soyuz version currently being used for most satellite launches (as distinct from crewed capsules or cargo capsules to the ISS) is a four-stage launch vehicle, which consists of:

  • four side boosters (booster stage)
  • a central core booster (first stage, which is lit at the same time as the side boosters, on the ground)
  • an upper (central) stage which is common to all Soyuz rockets regardless of payload
  • the re-startable Fregat “upper” stage (fourth stage) – this is not always used, for example it is not used with Soyuz spacecraft or Progress spacecraft

Side Boosters

The side boosters’ RD-107A engines are powered by liquid oxygen and kerosene, which are the same propellants used on each of the rocket stages. The kerosene tanks are located in the cylindrical part and the liquid oxygen tanks in the conical section. Each engine has four combustion chambers and four nozzles.

During side booster separation, the boosters perform a well-known pattern, in which they peel off and cartwheel outwards! This is known as the “Korolev cross,” which is named after Sergei Korolev, the Chief Design Engineer of the USSR space program in the 1960s.

Korolev cross during side booster stage separation on a Soyuz launch
“Korolev cross” seen during side booster stage separation on a Soyuz launch.

Soyuz Center Core

The center core is fitted with an RD-108A engine, and also has four combustion chambers and four nozzles. It also has four Vernier thrusters, used for three-axis flight control once the side boosters have separated. The third stage engine’s thrust enables the stage to separate directly from the central core. This is called “hot staging.”

Second Stage

The third stage uses either an RD-0110 engine in the Soyuz ST-A (2.1a) version or an RD-0124 engine in the ST-B (2.1b) version. This flight is using a 2.1b vehicle, so in this case, the stage has an RD-0124 engine.

Rocket-motor-RD-0124
RD-0124 motor at Salon-du-Bourget 2013. (Credit: Pline)

Soyuz Fregat Upper Stage

Flight qualified in 2000, the Fregat upper stage is an autonomous and flexible stage that is designed to operate as an orbital vehicle. It extends the Soyuz launcher’s capability, now covering a full range of orbits (LEO, SSO, MEO, GTO, GEO and Earth escape). Fregat is independent of all the other stages, as it has its own guidance, navigation, attitude control, tracking, and telemetry systems. The engine burns storable propellants – UDMH (unsymmetrical dimethylhydrazine) and NTO (nitrogen tetroxide) – and can be restarted up to 50 times in flight so that it can carry out very complex missions.

The Fregat upper stage is encapsulated in a fairing with the payload and a payload adaptor/dispenser. It is entirely independent from the rest of the rocket, having its own systems on board for guidance, navigation and control. It also provides its own telemetry data back to the ground.

Fregat uses the S5.92 engine, which uses unsymmetrical dimethyl hydrazine (UDMH) for fuel and nitrogen tetroxide (NO4) for oxidizer. The propellent is hypergolic, which means they combust on contact. The fuel and oxidizer will combust as soon as they meet in the combustion chamber.

Rocket section written by Andy Law

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