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|Proton launches third Blagovest satellite
The second and final mission of the Proton rocket in 2018 successfully delivered the Blagovest-13L satellite for the four-bird constellation of military communications spacecraft to be deployed in geostationary orbit 36,000 kilometers above the Earth's surface. The liftoff took place as planned on Dec. 21, 2018, at 03:20 Moscow Time.
Blagovest No. 13L mission at a glance:
Preparing the third and fourth Blagovest missions
On October 1, 2016, ISS Reshetnev announced the beginning of autonomous tests of the attitude control and stabilization system, SOIS, for the third Blagovest satellite.
On July 2, 2018, the head of the company Nikolai Testoedov said that the assembly of the satellite was scheduled to be completed in October 2018, so that its launch could take place from Baikonur after a 45-day campaign in December 2018. At the same time, the assembly and testing of the fourth satellite was expected to be completed in 2018 to enable its launch in the first quarter of 2019.
The launch of the third Blagovest was previously scheduled for November 2018, but the possibility of delays to as far as January 2019 was reported in July 2018.
In August 2018, industry sources said that third Blagovest would fly on December 22 of the same year. That date held for the rest of 2018 and the launch was even advanced by a day to Dec. 21, 2018.
Peculiarly, the launch of Blagovest-13L coincided with the planned shift to a new time zone of the Kzyl-Orda Region of Kazakhstan, the home of Baikonur Cosmodrome. The clock switch by one hour backwards to the fourth time zone (UTC/GMT +5 hours) was scheduled to take place at midnight from December 20 to December 21. However, according to the KazTAG news agency, the facilities in Baikonur would not make the switch until after the Blagovest launch set for 06:20 Astana Time (00:20 GMT) on December 21. The delay was required to keep the clocks in Baikonur synchronized with the processing and launch timeline of the upcoming Proton mission.
How Blagovest was launched
A Proton-M rocket with a Briz-M upper stage carrying Blagovest No. 13L lifted off from the snow-covered Pad 24 at Site 81 in Baikonur Cosmodrome on Dec. 21, 2018, at 03:20:00.020 Moscow Time (7:20 p.m. EST on December 20). The first, second and third stage of the launch vehicle operated for nine minutes and 40 seconds, releasing the payload section, including the upper stage and the satellite, into a ballistic trajectory just short of orbital velocity.
Around 10 minutes after the scheduled liftoff time, the official Russian press, quoting a statement from the Ministry of Defense, reported that a Proton-M rocket had been launched from Baikonur with a military spacecraft at 03:20 Moscow Time. According to the Ministry of Defense, ground assets of the Titov Chief Test Space Center of the Air and Space Forces, VKS, began tracking the vehicle at 03:25 Moscow Time.
A few minutes later, the Ministry of Defense also confirmed that the payload section with the space tug and the military satellite had separated from the third stage of the Proton-M vehicle as planned at 03:30 Moscow Time.
Around 1.5 minutes after the separation from the third stage, the Briz-M fired its own engine for less than four minutes to reach an initial parking orbit. It then made a swing around the Earth before firing again, this time for 17.7 minutes. The maneuver was designed to push the stack into a highly elliptical orbit, which the vehicle was to continue climbing for more than two hours.
The Briz-M's engine then fired again for nearly 18 minutes, this time, stretching the orbit so that its apogee (the highest point) ended up at the altitude of the geostationary orbit 36,000 kilometers above the Earth's surface. Shortly after the completion of its third maneuver, the space tug jettisoned its nearly empty external tank.
According to information from NORAD, the external tank from the Briz-M stage delivering Blagovest-13L was tracked in a 401 by 35,688-kilometer orbit with an inclination 48.67 degrees toward the Equator, as expected.
The remaining stack then climbed passively for five hours, before Briz-M initiated its fourth and final engine firing lasting slightly more than 13 minutes.
The maneuver was designed to circularize the orbit and tilt the orbital inclination to match the plane of the Equator, getting the spacecraft ready for separation from Briz slightly more than a minute after the fourth Briz firing.
After the successful release of the satellite, the Russian Ministry of Defense gave it an official designation Kosmos-2533.
Six days after the Dec. 21, 2918, launch, RIA Novosti news agency reported that the Briz-M had released the Blagovest-13L satellite into an orbit with some minor deviations from the required parameters. As of December 22, the satellite was tracked by NORAD in an 35,348 by 35,749-kilometer orbit with an inclination 0.19 degrees toward the Equator and an orbital period of 1,436 minutes (86,160 seconds).
According to Russian industry sources, the trajectory measurements showed that the actual orbital period (the time it takes the satellite to make a single revolution around the Earth) for Blagovest-13L was 720 seconds short of the planned number.
However, before launch, the mission control had already anticipated that the final orbital period for the payload could fall short up to 500 seconds, which flight planners could actually use to their advantage, when managing the easterly drift of the satellite toward its testing position in the geostationary orbit.
Because the 720-second deviation in the orbital period was causing the drift of the satellite in the same direction as the planned move, the "out-of-spec" orbital period could still be successfully compensated for during the planned initial adjustments of the satellite's orbit with its ion thrusters without overuse of xenon propellant, industry sources said. The same orbital corrections were also expected to fix a slight deviation in the eccentricity of the satellite's orbit (or deviation from a perfect circle). Briz-M left the satellite with a deviation in the eccentricity of 0.0047, which just within the required limit of 0.005. However, in order to gradually adjust the eccentricity, mission control had to divide the previously planned maneuvers, adding extra engine firings into the flight scenario.
Finally, the satellite's orbital inclination was required to be as close to zero as possible, to match its orbital plane with that of the Equator and thus eliminate any "wobbling" of the satellite's position in the sky for a ground observer and, more importantly, for communications antennas pointing at it. However, mission controllers hoped that no propulsion would be required to correct the 0.19-degree deviation thanks to the natural evolution of its orbit. Ballistic experts forecasted that by Jan. 20, 2019, the inclination would fall to 0.1 degree and by February 15, it would be reduced further to a mere 0.05 degree.
Peculiarly, Briz-M upper stages associated with all three Blagovest launches were tracked within a protected region of the geostationary orbit, where they were potentially posing a collision threat for operational satellites. The Briz-M stage that delivered Blagovest-13L satellite was tracked in an orbit, which had a perigee (lowest point) 230 kilometers above the geostationary altitude of 36,000 kilometers from Earth and an apogee 6,200 kilometers higher than the geostationary orbit. Clearly, Briz-M had performed some maneuvering after the release of the satellite, but, for some reason, fell short of reaching a safe burial orbit.
Blagovest satellite. Credit: ISS Reshetnev
A Blagovest satellite during assembly and testing. Credit: ISS Reshetnev
A Proton-M rocket with Blagovest No. 13L satellite on the launch pad in Baikonur. Click to enlarge. Credit: TsENKI
Blagovest No. 13L lifts off on Dec. 21, 2018. Click to enlarge. Credit: TsENKI