Soyuz launches fourth OneWeb cluster
After a nine-month hiatus caused by the coronavirus pandemic, the UK-based OneWeb company resumed the deployment of its low-orbital Internet-access constellation with the launch of a Soyuz-2-1b rocket carrying a batch of 36 fresh satellites. For the first time, the OneWeb cluster was launched from Russia's Vostochny Cosmodrome along a previously unused ground track. The liftoff took place as scheduled on December 18, 2020, at 15:26:26 Moscow Time (7:26 a.m. EST).
The fourth Soyuz mission with OneWeb satellites at a glance:
Preparing the fourth OneWeb mission
The fourth launch of OneWeb satellites, carrying 36 spacecraft, was expected to increase the Earth-orbiting constellation from 74 to 110 satellites, a step on the way to building a nearly 650-spacecraft network. The mission was designated ST29 to denote commercial Soyuz launches arranged by Arianespace's affiliate Starsem.
The OneWeb's first launch campaign in Vostochny kicked off on October 22, 2020, with the unpacking of the Fregat upper stage, which was mothballed at the center for several months. The space tug was installed at its work site inside the spacecraft processing center, MIK KA. Various support equipment, including spacecraft dispensers build by RUAG Space AB in Sweden to hold the satellites during their ride on the Soyuz rocket, landed at the Ignatievo airport in the city of Blagoveshensk aboard an Ilyusin-76 transport plane on November 2.
An Antonov-124-100 Ruslan transport plane with the 36 satellites intended for the launch departed Florida, where the spacecraft were built, on November 17. They arrived at Ignatievo on November 19, according to Roskosmos. On December 3, Roskosmos announced that its specialists had completed the pneumatic tests of the rocket's engines and begun electric tests.
In the meantime, the loading of the Fregat upper stage for the mission with propellant and pressurized gases was conducted at the fueling station from November 12 to December 1 and on December 4, the space tug was delivered to the spacecraft assembly building for the integration of the payload section.
Also, in the second half of November, all 36 OneWeb satellites were installed on their payload dispenser.
In early December, the launch was postponed from December 17, at 15:31:00 Moscow Time, to December 18, at 15:26:26 Moscow Time. (The launch window drifts five minutes forward with every 24-hour delay.)
OneWeb satellites are encapsulated under a payload fairing in Vostochny on December 11, 2020.
The satellite cluster was encapsulated under its payload fairing on December 11 and the payload section was transported to the vehicle assembly building on December 12. On the same day, it was integrated with the third stage of the Soyuz-2-1b rocket. After the assembly was completed with the connection between the third and the second stages on December 13, the rocket was given the green light for the rollout to the launch pad on December 14. The rocket made it to the pad as planned and was enclosed into the mobile service tower for most of the countdown to liftoff.
Planned countdown milestones for the ST28 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 similar timeline and flight parameters as those employed in the previous OneWeb launch from Baikonur. 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 used during the ascent to orbit was used for the first time by a Soyuz rocket launching from Vostochny.
The four boosters of the first stage should 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 separated at T+3 minutes 35 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 fired 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 allowed the third stage to reenter and fall back to the ground without reaching orbit.
Planned upper stage maneuvers
One minute after the separation from the third stage, the Fregat fired its main engine for 4 minutes and 7 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 major maneuver and the separation of the first batch of satellite was taking place out of contact with mission control.
Upon reaching the apogee of the transfer trajectory, Fregat was programmed to re-ignite its engine for 32 seconds to make its orbit circular at an altitude of around 450 kilometers.
The first pair of OneWeb satellites was released in opposite directions from their dispenser 1 hour 18 minutes and 20 seconds after launch.
In the following 15 minutes after the release of the first quartet of satellites, Fregat made a 15-second burn with its small attitude control thrusters to get in position for another release around three minutes later of four more satellites. The Fregat was programmed to repeat its thruster firing and 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.
At 18:30 Moscow Time (15:30 UTC, 10:30 a.m. EST), the Fregat reentered the communications range and mission control was able to confirm that the 3rd, 4th, 5th and 6th batch of OneWeb satellites successfully separated from their carrier. Then, still in direct view of ground stations, the 7th quartet also disembarked from Fregat, which Head of Roskosmos Dmitry Rogozin immediately confirmed to a wider public. However, the vehicle then went out of communications range for another 1 hour 18 minutes and 55 seconds.
The final four of 36 passengers separated from their space tug 3 hours 51 minutes and 40 seconds after their liftoff from Vostochny. But only at 20:03 Moscow Time (17:03 UTC, 12:03 p.m. EST), did the empty Fregat reappear in the view of ground stations and the successful separation of the 8th and 9th OneWeb quartets could be confirmed.
Around an hour after the release of the final quartet, the Fregat was 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 had to perform 11 active maneuvers: three with its main engine and eight firings of the SOZ attitude control thrusters.
As in all previous missions, the satellites had to use their own electric propulsion systems to climb to an operational orbit of around 1,200 kilometers.
Separation of the 8th batch of satellites from the Fregat upper stage.
Timeline of the ST29 mission on December 18, 2020:
During the active portion of the flight, the Fregat upper stage flew three times out of communications range with ground control:
Fourth OneWeb cluster attached to the Fregat upper stage is lowered in horizontal position in preparation for rolling its payload fairing, Click to enlarge. Credit: Roskosmos
Payload section with 36 OneWeb satellites is being prepared for integration with the third stage of the Soyuz-2-1b rocket on December 12, 2020. Click to enlarge. Credit: Roskosmos
Soyuz rocket with 36 OneWeb satellites shortly after arrival at the launch pad in Vostochny. Click to enlarge. Credit: Roskosmos
Soyuz-2-1b rocket lifts off from Vostochny on Dec. 18, 2020. Click to enlarge. Credit: Roskosmos
Less than 50 minutes after liftoff, Fregat left communications range of ground stations for 1 hours 18 minutes and 42 seconds. Click to enlarge. Credit: Roskosmos
Fregat conducted its second orbit correction before completing first orbit of the mission. Click to enlarge. Credit: Roskosmos
Separation of the 1st OneWeb cluster took place near the Equator during the first orbit of the mission. Click to enlarge. Credit: Roskosmos
Separation of the 2nd OneWeb cluster took place at end of the first orbit of the mission and was quickly confirmed by ground stations. Click to enlarge. Credit: Roskosmos
The second manuever with attitude control thrusters prepared the release of the third satellite quartet. Click to enlarge. Credit: Roskosmos
The separation of the third OneWeb quartet took place 1 hour 56 minutes after launch. Click to enlarge. Credit: Roskosmos
A T+02:12:30, Fregat conducted its 3rd maneuver with its SOZ thrusters lasting 12 seconds. Click to enlarge. Credit: Roskosmos
The separation of the fourth OneWeb quartet took place 2 hour 15 minutes after launch. Click to enlarge. Credit: Roskosmos
A T+02:31:40, Fregat conducted its 4th maneuver with its SOZ thrusters lasting 11 seconds. Click to enlarge. Credit: Roskosmos
The separation of the fifth OneWeb quartet took place 2 hour 35 minutes after launch. Click to enlarge. Credit: Roskosmos
A T+02:50:50, Fregat conducted its 5th maneuver with its SOZ thrusters lasting 10 seconds. Click to enlarge. Credit: Roskosmos
The separation of the sixth OneWeb quartet took place 2 hour 54 minutes and 10 seconds after launch. Click to enlarge. Credit: Roskosmos
A T+03:10:00, Fregat conducted its 6th maneuver with its SOZ thrusters lasting 8 seconds. Click to enlarge. Credit: Roskosmos
The separation of the 7th OneWeb quartet took place 3 hours 13 minutes and 20 seconds after launch. Click to enlarge. Credit: Roskosmos
A T+03:29:10, Fregat conducted its 7th maneuver with its SOZ thrusters lasting 7 seconds. Click to enlarge. Credit: Roskosmos
The separation of the 8th OneWeb quartet took place 3 hours 32 minutes and 30 seconds after launch. Click to enlarge. Credit: Roskosmos
A T+03:48:20, Fregat conducted its 8th maneuver with its SOZ thrusters lasting 6 seconds. Click to enlarge. Credit: Roskosmos
The separation of the 9th OneWeb quartet took place 3 hours 51 minute and 40 seconds after launch. Click to enlarge. Credit: Roskosmos