Soyuz launches eighth OneWeb cluster
A Soyuz-2-1b/Fregat rocket is delivering a fresh batch of 36 satellites for the UK-based OneWeb company after lifting off on July 1, 2021, from Vostochny Cosmodrome. It is the fourth launch of the year into the OneWeb constellation, boosting it from 218 to 254 spacecraft.
The eighth Soyuz mission with OneWeb satellites at a glance:
Preparing the eighth OneWeb mission
According to OneWeb, with 254 satellites in orbit — the number to be achieved with the successful eighth mission, which was dubbed "Hello North Pole" — the company would be able to provide a complete Internet connectivity for clients located above the 50th parallel of our planet, including the North Pole, as early as the end of 2021. Hence, the logo designed for the mission and its name.
The rocket for the eighth OneWeb mission was one of the two launch vehicles shipped to the spaceport from the production factory at RKTs Progress during the night from May 6 to May 7, 2021.
On May 21, specialists from its Vostochny branch of the TsENKI ground infrastructure center and NPO Lavochkin had transported the Fregat upper stage for the mission from the spacecraft processing building, MIK KA, to the fueling station. According to Roskosmos' announcement on May 25, the fueling operations were scheduled to begin in the near future and be completed by June 18.
The satellites for the mission were ready for departure to the launch site on June 8, 2021, and Roskosmos confirmed that they had arrived at the Ignatievo airport near Vostochny on June 10.
The assembly of the first and second stage boosters for the mission was performed on June 14 and the payload section with all 36 satellites and the Fregat upper stage was fully assembled by June 24, 2021. The next day, the payload section was transferred from the spacecraft processing hall to the vehicle assembly building for integration with its Soyuz-2 rocket, which was completed on June 25. The fully assembled vehicle was then loaded on its transporter-erector for a trip to the launch pad. The rollout of the vehicle to the launch pad took place as scheduled on the morning of June 28. In the long-established tradition, the rocket left the assembly building at 07:00 local time (01:00 Moscow Time).
Operations on the pad
Upon arrival to the pad, the rocket rocket was raised upright, and the mobile service tower was moved into position around the vehicle. In the course of the first day on the pad, personnel were scheduled to connect measurement and flight control cabling to the rocket, as well as fueling and pneumatic lines. The autonomous checks of the Fregat upper stage and, one hour later, of the rest of the rocket were also planned. The integrated tests of the rocket and the launch simulation were completed during the second day on the pad.
On June 30, the personnel performed a battery checks aboard the OneWeb satellites and flushed the fueling system with high-concentration hydrogen peroxide starting at 11:15 Moscow Time. This was followed by the attachment of fueling lines to the rocket and final operations.
The State Commission was scheduled to convene for the final time before launch on July 1 to clear the rocket for fueling and liftoff.
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.
The ascent profile of the mission had a timeline and flight parameters similar to those employed in the previous OneWeb launches 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 (L+117.8 sec.), but the core booster of the second stage continued firing until 4 minutes and 48 seconds into the flight (L+287.5 sec.). In the midst of its operation, the payload fairing protecting the payload in the dense atmosphere split into two halves and dropped off at T+3 minutes 35 seconds (L+214.8 sec.). Immediately after the separation of the second stage, the aft section of the third stage split into three fragments and separated at L+292.1 seconds.
The fragments of the rocket were 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 continued firing until 9 minutes and 22 seconds into the flight, releasing the Fregat upper stage and its cargo on a ballistic trajectory with an apogee of 249 kilometers, just short of orbital velocity at L+561.8 seconds. This allowed the third stage to reenter and fall back to the ground at a predicted remote area of the ocean instead of reaching orbit.
Upper stage maneuvers
One minute after separation from the third stage, Fregat should fire its main engine for 307 seconds to enter an elliptical (egg-shaped) 150 by 427-kilometer transfer orbit with the highest point (apogee) near the target altitude for the release of OneWeb satellites.
After its first maneuver, Fregat will climb passively for nearly an hour. Soon after an orbital insertion, the space tug and its passengers will leave the communications range of ground stations for 1 hours 18 minutes and 42 seconds, therefore Fregat's second maneuver and the separation of the first batch of satellites will be taking place out of contact with mission control. The restart of the Fregat's engine for a 31-second firing will then happen near the apogee of the transfer orbit making it circular at an altitude of around 450 kilometers.
The first quartet of OneWeb satellites will be released in opposite directions from their dispenser 1 hour 18 minutes and 20 seconds after launch. It will be followed nearly 16 minutes later by a 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.
Fregat is programmed to repeat its thruster firing and the four-satellite release routine seven more times, evenly distributing quartets of satellites along their orbit.
When the Fregat reenters the communications range, mission control should be able to confirm that the 3rd, 4th, 5th and 6th batch of OneWeb satellites had indeed 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 again go out of communications range for another 1 hour 18 minutes and 55 seconds.
The final four of the 36 OneWeb 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, 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 is scheduled to 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.
Timeline of the OneWeb mission on May 28, 2021:
The official logo of the eighth OneWeb mission, ST33. Credit: OneWeb
Payload arrangement for the OneWeb launch on the Soyuz rocket with 36 satellites. The satellites are attached to a 5.5-meter-tall, 1.7-meter-in-diameter adapter built by RUAG Space. Credit: Arianespace
Fregat upper stage for the eighth OneWeb mission is transported to the fueling station on May 21, 2021. Click to enlarge. Credit: Roskosmos