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Soyuz launches the 10th OneWeb cluster

A Soyuz-2-1b/Fregat rocket lifted off Tuesday from Baikonur Cosmodrome in Kazakhstan with a batch of 34 satellites for the UK-based OneWeb company. It is the 10th mission overall and the sixth launch of the year to build the OneWeb constellation, expanding it from 288 to 322 spacecraft.


The 10th Soyuz mission with OneWeb satellites at a glance:

Mission and spacecraft designation
ST35 OneWeb (Satellites 289 - 322)
Launch vehicle
Soyuz 2-1b / Fregat No. 123-05
Payload fairing
81KS 1000-0 No. Ya15000-042
Launch site
Launch date and time
2021 Sept. 14, 21:07:19.121 Moscow Time
Payload mass (including dispenser)
34 OneWeb satellites, 5,510 kilograms total
Target orbit
Altitude: ~450 kilometers, inclination 87.4 degrees*

*Satellites will use their own propulsion system to enter a 1,200-kilometer operational orbit



Preparing the 10th OneWeb mission


A cluster of 34 satellites for the 10th OneWeb mission was integrated with its Fregat upper stage on Sept. 3, 2021.

The 10th OneWeb launch was originally planned for August 26 but by mid-August 2021, the mission slipped until September 14.

On July 9, 2021, Roskosmos announced that personnel of the Yuzhny space center in Baikonur and RKTs Progress had completed the integration of the first and second stages of the launch vehicle for the mission. The batch of 34 OneWeb satellites arrived at Baikonur aboard An-124 transport plane on August 25, 2021.

The seven-day process of loading propellant components aboard the Fregat upper stage for the flight was completed at the fueling facility of Site 31 by August 29, 2021. On the morning of September 1, the space tug was transferred to the processing building at Site 112 for integration of the payload section. By September 2, the payload fairing for the mission was assembled at the processing building at Site 112 and was also ready for integration with the satellites. All the components were then moved inside a clean room facility at Site 112, used for integration of OneWeb payloads. Here, on September 3, the payload dispenser holding the cluster of 34 satellites was mated with Fregat and, in the following day, after the completion of electric checks, the stack was rotated into horizontal position and rolled inside its payload fairing. On September 7, the payload section was reloaded from its work site inside processing building at Site 112 onto a railway platform and transported to Site 31 for integration with the launch vehicle.


On September 10, Roskosmos announced that the State Commission overseeing the preparations for the launch had given the go ahead to the rollout of the rocket to the pad, which took place on the morning of September 11.

Launch profile of the OneWeb mission originating from Baikonur


A Soyuz-2-1b rocket with a Fregat-M upper stage and carrying a cluster of 34 OneWeb satellites lifted off as scheduled from Site 31 in Baikonur on Sept. 14, 2021, at 21:07:19 Moscow Time (2:07 p.m. EDT).

After a few seconds of vertical ascent, the launch vehicle headed northward, across Kazakhstan and Russia to align its ascent trajectory with a near-polar orbit inclined 87.4 degrees toward the plane of the Equator.

The four boosters of the first stage separated T+117.8 seconds after liftoff, but the core booster of the second stage continued firing until 287.5 into the flight. It separated moments after the ignition of the third stage. Less than two seconds later (T+289.2 seconds), the tail section of the third stage split into three segments and separated as well. Another second later (T+290.4 seconds), the payload fairing, which protected the payload in the dense atmosphere, split in the two fragments and fell off.

The third stage completed its firing and separated at T+563.8 seconds, releasing the Fregat upper stage and its cargo on a ballistic trajectory with a highest point 191 kilometers above the Earth's surface, but just short of orbital velocity. It allowed the third stage to reenter and fall into a projected area of the Arctic Ocean, north of the Canadian coast.

Exactly one minute after the separation from the third stage, the Fregat fired its main engine for 4 minutes and 11 seconds entering a transfer elliptical (egg-shaped) orbit with the lowest point (perigee) 140 kilometers above the Earth and the highest point (apogee) 425 kilometers above's the Earth's surface, which was near the target altitude for the release of OneWeb satellites.

Upper stage maneuvers


After its first maneuver, the Fregat climbed passively for nearly an hour. Upon reaching the apogee of the transfer trajectory, Fregat re-ignited its engine for 34 seconds making its orbit circular at an altitude of around 450 kilometers.

Then, 1 hour 11 minutes and 40 seconds after launch, the first pair of OneWeb satellites was released in opposite directions from their dispenser.

In the following 15 minutes, Fregat made a 15-second burn with its small attitude control thrusters to get in position for another release around three minutes later, this time, of four satellites.

Roskosmos confirmed that the deployments of first two groups of satellites had taken place as planned at 22:18 and 22:38 Moscow Time on September 14.

The Fregat then repeated its thruster firing and release routine seven more times, evenly distributing the quartets of satellites along their orbit. The final four of 34 passengers were scheduled to be off their space tug 3 hours and 45 minutes after their liftoff from Baikonur.

According to Roskosmos, the third, fourth, fifth and sixth quartets were successfully separated at 23:16, 23:35, 23:54 Moscow Time on September 14 and at 00:13 Moscow Time on September 15, respectively. The eighth group of satellite was released at 00:33 Moscow Time. Finally, four satellites from the ninth group also disembarked as planned, completing the mission, according to Roskosmos.

Around 1 hour and 20 minutes after the release of the final quartet, the Fregat was programmed to initiate a braking maneuver which was designed to push the stage on a disposal orbit, resulting in its quick destruction in the upper atmosphere nearly six hours after launch.

Following their release, the satellites were expected to maneuver to their operational orbits 1,200 kilometers above the Earth's surface, using onboard electric thrusters.


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Page author: Anatoly Zak; Last update: January 1, 2022

Page editor: Alain Chabot; Last edit: September 14, 2021

All rights reserved


insider content



Payload arrangement for the OneWeb launch on the Soyuz rocket with 34 satellites. The satellites are attached to a 5.5-meter-tall, 1.7-meter-in-diameter adapter built by RUAG Space. Credit: Arianespace


Official logo for the tenth OneWeb mission. Credit: Arianespace


Fregat upper stage for the 10th OneWeb mission undergoes fueling in August 2021. Click to enlarge. Credit: Arianespace