Soyuz launches fifth OneWeb cluster
The deployment of the Internet-delivery satellite constellation for the UK-based OneWeb company resumed in 2021 with the launch of a Soyuz-2-1b rocket carrying a fresh batch of 36 satellites. Originating from Russia's Vostochny Cosmodrome, the fifth OneWeb mission lifted off on March 25, at 05:47 Moscow Time.
The fourth Soyuz mission with OneWeb satellites at a glance:
Preparing the fifth OneWeb mission
The fifth OneWeb launch would increase the number of satellites in the constellation from 110 to 146 satellites out of planned 650 spacecraft. The mission had a designation ST30 in the naming system used by Arianespace and its affiliate Starsem, which managed the campaign. The launch was initially planned for February 25, 2021, but by the end of January, it was postponed until March 25, 2021. A fresh batch of 36 satellites arrived at the Ignatievo airfield near the city of Blagoveshensk aboard an An-124 transport plane on February 26, 2021. From Ignatievo, trucks delivered satellites to Vostochny, kicking off a month-long launch campaign.
By March 10, all 36 satellites had been attached one by one to their payload dispenser inside the spacecraft processing building, and the cluster was ready for integration with its the Fregat upper stage and the payload fairing. The resulting payload section was then moved to the vehicle assembly building and integrated with the third stage of the Soyuz-2-1b rocket on March 18, followed by the final assembly of the vehicle and its loading on the transporter-erector on March 19. On March 20, the State Commission overseeing the campaign met and gave the green light to the rollout of the rocket to the launch pad, which took place on the morning of March 22, 2021.
Due to controversies often surrounding space activities in rural areas of Russia, Roskosmos publicized environmental monitoring activities around the impact sites. According to the State Corporation, a group of experts from Roskosmos and the environmental ministry of the Yakut Republic were dispatched to the drop zone of rocket parts, to be used during the launch, to take soil and snow samples for radiation and contamination tests. Due to bad weather helicopter flights to Kobyask and Aldan districts had to be postponed until March 22 and 23. The soil sampling and radiation measurements would then be repeated in the area after the launch.
On March 24, Roskosmos announced that the previous day, the launch vehicle had passed the general tests with flying colors, as well as a simulation of the three-stage ascent process. At 02:50 Moscow Time (08:50 local), members of the personnel took their positions at the launch complex and started the third day of operations on the pad with checks of battery charges on 36 satellites to be delivered in the mission.
The main activity included flushing of the propellant loading lines with high-concentration hydrogen peroxide (initiated at 06:00 Moscow Time) and the fuel cooling. The specialists then attached propellant loading lines to the rocket and conducted final operations.
The meeting of the State Commission overseeing the tests was scheduled for the night from March 24 to 25, when the decision would be made to proceed with the fueling of the rocket, Roskosmos said. The fueling operations were scheduled to start at 01:20 Moscow Time on March 25, 2021.
Final assembly of the Soyuz rocket for the 5th OneWeb mission in Vostochny on March 19, 2021.
Planned countdown milestones for a typical OneWeb mission, according to Arianespace:
Launch profile of the OneWeb mission originating from Vostochny
Approximate ground track of the OneWeb mission.
A Soyuz-2-1b rocket carrying a cluster of 36 OneWeb satellites lifted off as scheduled from 1S pad in Vostochny on March 25, 2021 at 05:47:33.180 Moscow Time (11:47 local time, 02:37 UTC). (It will be 10:47 p.m. EDT on March 24.)
The ascent profile of the mission had a similar timeline and flight parameters as those employed in the previous OneWeb launch from Vostochny. After a few seconds of vertical ascent, the launch vehicle headed northward to align its ascent trajectory with a near-polar orbit inclined 87.4 degrees toward the plane of the Equator. The particular ground track employed during the ascent to orbit from Vostochny had so far been unique to OneWeb missions.
The four boosters of the first stage separated 1 minute and 58 seconds after liftoff, but the core booster of the second stage continued firing until 4 minutes and 48 seconds into the flight. In the midst of its operation, the payload fairing protecting the payload in the dense atmosphere split into two halves and drop off at T+3 minutes 35 seconds.
The fragments of the rocket are expected to fall at Drop Zones No. 873 and 875 in the Aldan and Kobyask Districts of the Sakha (Yakut) Republic in the Russian Far East.
The third stage will continue firing until 9 minutes and 22 seconds into the flight, releasing the Fregat upper stage and its cargo on a ballistic trajectory, just short of orbital velocity. This will allow the third stage to reenter and fall back to the ground at a predicted remote area of the ocean instead of reaching orbit.
Planned upper stage maneuvers
One minute after the separation from the third stage, the Fregat fired its main engine for 307 seconds to enter an elliptical (egg-shaped) transfer orbit with a lowest point (perigee) of around 140 kilometers above the Earth and the highest point (apogee) of around 425 kilometers above the Earth's surface, which is near the target altitude for the release of OneWeb satellites.
After its first maneuver, the Fregat climbed passively for nearly an hour. Soon after an orbital insertion, Fregat left communications range of ground stations for 1 hours 18 minutes and 42 seconds, therefore its second maneuver and the separation of the first batch of satellites took place out of contact with mission control. The restart of the Fregat's engine for a 31-second firing took place near the apogee of the transfer orbit and made it circular at an altitude of around 450 kilometers.
The first quartet of OneWeb satellites was then released in opposite directions from their dispenser 1 hour 18 minutes and 20 seconds after launch. It was followed nearly 16 minutes later by the 15-second firing of the small attitude control thrusters, SOZ, aboard Fregat to get the vehicle in position for the second quartet drop around three minutes later.
The Fregat was programmed to repeat its thruster firing and the four-satellite release routine seven more times, evenly distributing quartets of satellites along their orbit.
The fourth batch of OneWeb satellites separate from the Fregat upper stage.
When the Fregat would reenter the communications range, mission control will be able to confirm that the 3rd, 4th, 5th and 6th batch of OneWeb satellites separated from their carrier. Then, still in direct view of ground stations, the 7th quartet will also disembark from the space tug. However, the vehicle will then go out of communications range for another 1 hour 18 minutes and 55 seconds.
The final four of 36 passengers will separate from their space tug 3 hours 51 minutes and 40 seconds after their liftoff from Vostochny. But the empty Fregat will reappear in the view of ground stations later making it possible to confirm the separation of the 8th and 9th OneWeb quartets.
Around an hour after the release of its final passengers, the Fregat is programmed to initiate a braking maneuver with its main engine designed to push the stage on a disposal orbit, resulting in its quick destruction in the upper atmosphere nearly six hours after launch over a remote area of the Pacific Ocean. In total, Fregat will perform 11 active maneuvers: three with its main engine and eight firings of the SOZ attitude control thrusters.
As in all previous missions, OneWeb satellites will have to use their own electric propulsion systems to climb to an operational orbit of around 1,200 kilometers.
In the post-launch press-release, NPO Lavochkin announced that the Fregat upper stage had completed the third firing of its main engine around five hours after launch, directing itself on a reentry trajectory over the remote area of the Pacific Ocean.
Separation of the 8th batch of satellites from the Fregat upper stage.
Timeline of the ST29 mission on December 18, 2020:
During its active portion of the flight with OneWeb satellites originating from Vostochny, the Fregat upper stage goes out of communications range with ground control three times:
Payload arrangment for the OneWeb launch on Soyuz rocket with 36 satellites. Credit: Arianespace
The fifth OneWeb cluster and its preparation team. Click to enlarge. Credit: Roskosmos
The fifth OneWeb cluster is encapsulated under its payload fairing. Click to enlarge. Credit: Roskosmos
Soyuz lifts off on March 25, 2021. Click to enlarge. Credit: Roskosmos