Soyuz delivers ninth OneWeb cluster
A Soyuz-2-1b/Fregat rocket delivered a batch of 34 satellites for the UK-based OneWeb company in early hours of August 22, 2021, from Baikonur Cosmodrome in Kazakhstan. Around 48 hours earlier, the mission was aborted less than a minute before its scheduled liftoff due to a technical problem. It is the fifth mission of the year to build the OneWeb constellation, boosting it from 254 to 288 spacecraft.
The ninth Soyuz mission with OneWeb satellites at a glance:
Preparing the ninth OneWeb mission
On May 4, 2021, Roskosmos announced that the integration of the four boosters comprising the first stage of the Soyuz-2 rocket with the core booster of its second stage had been completed at the vehicle assembly building at Site 31 by a joint team ofthe Yuzhny branch of the TsENKI infrastructure center and RKTs Progress, the Soyuz rocket developer. At the time, this particular vehicle was in the storage mode, awaiting the start of the launch campaign. On July 9, Roskosmos announced that the launch vehicle for the ninth OneWeb mission had been placed on its processing work site in preparation for the final assembly. In early July, a delay in the satellites' shipment to Baikonur until July 28, required postponing the launch from early August to August 20.
The satellites for the mission arrived at the Krainiy airport by July 30, 2021. On Aug. 6, 2021, Roskosmos announced that specialists from the Yuzhny branch of the TsENKI ground infrastructure center at Site 31's fueling station had completed the seven-day process of loading the Fregat upper stage for the mission with propellant components and pressurized gases, and that vehicle had been returned to the spacecraft processing building at Site 112 for integration with its payload. The assembly of the payload section was completed by August 10. On August 13, Roskosmos announced the completion of the launch vehicle assembly. It was rolled out to the launch pad on the morning of August 16.
The integration of the two booster stages for the Soyuz rocket assigned to launch the ninth OneWeb mission was completed on May 4, 2021.
Operations on the pad
Upon arrival to the pad on August 16, the rocket rocket was raised upright and personnel connected measurement and flight control cabling to the rocket, as well as fueling and pneumatic lines.
The work on the pad on August 17 focused on final checks of all systems and concluded with integrated tests of the rocket and the launch facility, simulating the countdown and ascent of the vehicle until the separation of the spacecraft in the target orbit. All the data was then analyzed, Roskosmos said.
During August 18, which was considered a "back-up day", as well as in the first half of the day on August 19, the main activity included thermal conditioning of "naftil" (a Russian term for a rocket-grade kerosene), which was delivered to the pad in a 11G133 mobile road tanker.
The State Commission convened for the final time before launch on the evening of August 19, clearing the rocket for fueling and liftoff on August 20, 2021, at 01:23:17 Moscow Time.
On August 20, all preparations for launch went as planned, however 40 seconds before a scheduled liftoff, the automated sequence was interrupted. Publicly broadcast voice communications of the launch personnel at the time indicated that the launch abort was accompanied by the AVD command, which stands for Avariynoe Vyklyuchenie Dvigatelei or emergency engine cutoff. That usually means that propellant components had already filled the engine tracts and could require to remove the rocket from the pad to drain the engines.
However, shortly after the abort, Roskosmos announced that a new attempt to launch the mission would be made on August 21, at 01:18:20 Moscow Time. It appeared that the AVD command was issued prematurely, because live images showed that around seven or eight seconds after the zemlya-bort (ground-vehicle) command and the subsequent switch of the Block I third stage to internal power supply, there was opening of the valves indicating the shutdown of the launch sequence, observers noted. It was followed by the delayed retraction of the umbilical mast from the third stage, which likely triggered the abort.
In any case, by the end of the workday in Moscow on August 20, Head of Roskosmos Dmitry Rogozin announced another 24-hour delay "on the request from a foreign customer due to lack of readiness of its ground measurement assets." Around the same time, Arianespace announced that the launch "has been postponed to allow for additional mission planning preparation following the updated lift-off. The launch vehicle and 34 satellites remain in safe and stable conditions," Arianespace said.
According to Roskosmos, the fueling of the launch vehicle for another launch attempt proceeded as scheduled in late hours of August 21.
Launch profile of the OneWeb mission originating from Baikonur
After a few seconds of vertical ascent, the launch vehicle headed northward, across 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+117.9 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 was programmed to fire its main engine for 4 minutes and 11 seconds to enter 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 is 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. 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.
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 positions 1,200 kilometers above the Earth's surface, using onboard electric thrusters.
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
Logo for the 9th OneWeb mission. Credit: OneWeb
Payload section for the ninth OneWeb misison and its processing specialists at clean room facility in Baikonur. Click to enlarge. Credit: Arianespace
Payload section of the 9th OneWeb mission after completion of its assembly on August 9, 2021. Click to enlarge. Credit: Roskosmos
Integration of the upper composite with the booster stages of the Soyuz-2-1b rocket for the 9th OneWeb mission on on August 13, 2021. Click to enlarge. Credit: Roskosmos