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Proton launches a pair of Russian communications satellites In its second and final mission of 2021, a Proton rocket lifted off from Baikonur with two Ekspress communications satellites on Dec. 13, 2021. After more than 18-hour delivery process, the rocket's Briz-M upper stage released the Ekspress-AMU3 and -AMU7 satellites into a high deployment orbit extending more than 50,000 kilometers from Earth.
Proton launch with Ekspress-AMU3 and -AMU7 satellites at a glance:
Newest pair of Ekspress satellites The Ekspress-AMU3 and -AMU7 satellites were built at ISS Reshetnev in the city of Zheleznogorsk for the main Russian state-owned operator of civilian communications satellites Kosmicheskaya Svyaz, GPKS. According to the official procurement documentation, GPKS paid 72 million Euro for the pair. They were the first of as many as 14 satellites promised to be launched during the 2020s to modernize Russian space communications assets. Typically for the Ekspress series, AMU3 and AMU7 were designed for providing stationary and mobile clients, among them the Russian government, with a variety of communications services, including digital TV and radio broadcasts, high-speed Internet access, with coverage extending across Russia and adjacent regions in C-, Ku and L-bands. The spacecraft use two deployable antennas with reflectors 2.4 and 2.2 meters in diameter. One is the multi-beam antenna operating in Ku-band, the other combines C- and Ku-bands. The satellites also have a dedicated L-band arrays. The service module for both satellites was based on Reshetnev's Ekspress-1000N platform, which allows two satellites to be stacked on top of each other for a shared ride to orbit on a single Proton-M/Briz-M rocket. One major difference from previous service modules in the series was the introduction of heat pipes replacing liquid coolant in the thermal control system. The vehicle's propulsion system was also upgraded with a single 29-gramm SPD-140D electric engine, in addition to a pair of SPD-100V engines all developed at OKB Fakel in Kaliningrad. The trust increase from 8 grams, delivered by each SPD-100V engine, enabled cutting the time needed for the transfer of the satellites from the deployment orbit to the operational position. The platform was equipped with a pair of solar panels built by Reshetnev and featuring gallium arsenide elements developed at NPP Kvant in Moscow. Initially, both satellites were expected to carry 20 C-band transponders, 16 Ku-band transponders and 1 L-band transponder. Ekspress-AMU7 was to be stationed over an equatorial point 145 East longitude and Ekspress-AMU3 would be deployed at 96.5 East. However, according to pre-production plans made after the Kremlin's annexation of Crimea in 2014, the Ekspress-AMU7 would be built first and carry a communications payload already procured from the Italian division of Thales Alenia Space, in the traditional Russian-European industrial partnership. In the meantime, the follow-on Ekspress-AMU3 was to be equipped with Russian-built transponders replacing banned European hardware. These plans never materialized, but in 2018, Reshetnev was able to strike a deal with Thales to supply antennas and transponder payloads for both satellites. Only in case of AMU7, for the first time, Thales Alenia ordered a 2.4-meter reflector from Reshetnev to be made from composite materials for the satellite's C-band antenna. Around the same time, Roskosmos made plans to switch the satellites from a single Proton to the third and fourth or fourth and fifth test flights of Angara-5/Persei rockets from Plesetsk. Roskosmos officials apparently saw the AMU3/7 mission as an opportunity for giving the Angara a real job, demonstrating the new rocket's validity for the international market. However, Russian communications officials reportedly pushed back, not willing to rely on an unproven and chronically delayed launch system for the costly mission. In 2019, after at least a year of wrangling and conflicting orders from Roskosmos, it took a special decision of the Russian government to re-assign the satellites back to a single Proton which had been manufactured in 2013 for a later cancelled GLONASS-M mission. By 2020, the planned orbital position for Ekspress AMU-3 was shifted to 103 degrees East longitude which was previously occupied by the ailing Ekspress-AM3 satellite launched in 2005 and was to be assigned to the Ekspress-103 satellite. Ekspress-AMU7 would still be stationed at 145 degrees East, replacing the defunct Ekspress-A4 spacecraft launched in 2002.
Known specifications of the Ekspress-AMU7 and AMU3 satellites:
In its final configuration, Ekspress-AMU7 was equipped with 16 active and two additional C-band transponders operating on backup equipment and two beacons; 20 Ku-band linear transponders and one beacon and one L-band active transponder, all capable of simultaneous operation. In the meantime, Ekspress-AMU3 received seven active C-band transponders and two active L-band transponders. The Ku-band payload has a transformable architecture. In the first configuration, it operates eight active transponders and in the second - 22. The communications payloads on both satellites were designed to receive radio signals from the ground, to amplify them with low interference, convert the received signal based on the bandwidth of the operational channel and then re-transmit the signal back to the ground. Development and launch campaign During the early planning for the AMU-3 and -7 development, their launch was penciled for 2016, but when the satellites appeared in the Russian Federal Space Program, which was approved in the mid-2010s, they were not expected to fly before 2018. However, by that time the production of the satellites was only starting at ISS Reshetnev and Thales Alenia Space. The completed communications payloads for AMU7 and AMU3 were scheduled for delivery to ISS Reshetnev from Thales Alenia Space, Italy, in March and May 2020, respectively. The fully equipped solar panels arrived at ISS Reshetnev from NPP Kvant early in 2020 and the service modules were cleared for tests. By the middle of the same year, the service module and the payload section of AMU7 were bolted together and it entered integrated electrical tests. Due to coronavirus restrictions, specialists from Thales had to participate in the tests remotely for the first time via a specially installed video cameras . At the time, the mission was expected in the second quarter of 2021. The assembly of the sister AMU3 satellite was completed in November 2020, and by that time, the launch of the dual payload had slipped toward the end of 2021. In early 2021, AMU7 underwent acoustic trials and high-frequency radio tests in the anechoic chamber. Roughly in parallel, AMU3 was going through electric and thermal tests, followed by vibration tests at the end of the Summer and by radio tests in the Fall of 2021. By September 2021, the launch of the two satellites was set for December 6. The Proton-M and Briz-M vehicles for the AMU3/AMU7 mission departed the production plant at GKNPTs Khrunichev in Moscow for Baikonur during the night from March 15 to 16, 2021, along with the three-stage Proton-M rocket assigned for the launch of the MLM Nauka module. The Ekspress-AMU-3 and -7 satellites arrived at Baikonur on October 19, landing at the Krainy airfield aboard an An-124 aircraft. They were then transported to Site 92 for initial processing. On October 30, the Ekspress-AMU3 satellite was transported to the fueling station at Site 91A, where it was loaded with propellant components. On November 1, Roskosmos announced that fueling operations had been completed and the spacecraft was scheduled to be delivered to the processing building at Site 92A for measuring the resistance of onboard power buses, checks of heater integrity and inspection of the solar panel mechanisms, Roskosmos said. It was unclear from the announcement whether these were standard launch campaign procedures or had they been prompted by some technical problems. In the same release, Roskosmos confirmed the planned launch of the mission in December 2021 but did not quote the December 6 launch date. The two-day fueling operations with Ekspress-AMU7 satellite were concluded at Site 91A by November 5. The satellite was then brought to the processing building at Site 92A for loading of xenon gas, Roskosmos said. (Xenon is used by the satellite's electric engines.) Around mid-November, the launch was postponed from Dec. 6, 2021, at 15:20 Moscow Time, to December 12, at 15:09 Moscow Time, due to problems with the Briz-M upper stage. On November 23, Roskosmos announced that the instruments aboard the upper stage had been replaced inside the processing building at Site 92A-50 and that the electrical tests of the stage had been completed. The three booster stages of the rocket had also been assembled inside the processing hall of the same building, Roskosmos said. On November 25, Roskosmos said that the high-pressure tanks aboard the Briz-M were being loaded with propellant components and by December 2, both spacecraft were installed on the upper stage. The stack was then covered with a payload fairing and moved to the final assembly hall, where on December 5, it was integrated with the booster stages of the Proton rocket, followed by electrical checks, connections of the thermal control hoses and the installation of thermal blankets on the payload fairing.
A Proton rocket with Ekspress AMU-3 and AMU-7 satellites arrives at the launch pad No. 39 at Site 200 on Dec. 9, 2021. Fatal propellant overload discovered aboard Briz-M Upon completion of the assembly, the Proton/Briz vehicle was prepared for the rollout from the vehicle assembly building to the outdoor fueling pad for loading low-pressure tanks of the Briz-M upper stage with highly toxic and dangerous hypergolic propellant components. The rollout operation took place on the morning of December 9, 2021. After the fueling of the Briz-M, the vehicle proceeded to Pad 39 at Site 200, where it was installed in a vertical position by the end of the day. However, shortly thereafter, another technical problem with the Briz-M stage forced the return of the rocket from the pad and the postponement of the launch. According to the head of Roskosmos Dmitry Rogozin, at least two issues were discovered with the space tug.
A Proton rocket with Ekspress AMU-3 and AMU-7 satellites at the Briz fueling pad. Russian officials never provided any details on the incident, but well-informed industry sources said that the propellant overload had been discovered aboard the Briz-M stage, which was reminiscent of the situation which doomed the launch of three GLONASS navigation satellites aboard a Proton/Block-DM03 vehicle in December 2010. Fortunately, this time, the embarrassing and potentially fatal issue was detected well before liftoff, but it still required the removal of the entire vehicle from the pad and its return to the outdoor fueling pad where extra propellant was carefully drained from the upper stage on December 10, before the rocket could be returned to the pad. Within 24 hours from the discovery of the problem, Rogozin said that the rocket would be returned to the pad on December 11 with the possibility of the launch on December 13. On December 11, Roskosmos confirmed that the mission had been scheduled for liftoff on December 13, at 15:07 Moscow Time. The second rollout of the rocket to the pad started at 04:30 Moscow Time on December 11. Launch profile  A Proton-M/Briz-M rocket carrying the Ekspress-AMU-3/AMU-7 pair lifted off from Pad 39 at Site 200 at Baikonur Cosmodrome on Dec. 13, 2021, at 15:07:00 Moscow Time (7:07 a.m. EST) After several seconds in vertical ascent, the Proton headed east along a standard ascent trajectory, which enabled it to reach an orbital inclination of 51.55 degrees toward the Equator. The firing of the first, second and third stages of the rocket inserted the payload section, comprising the Briz-M stage and the two satellites into a suborbital trajectory, just short of orbital velocity. Nearly 1.5 minute after the separation from the third stage, Briz-M fired its main propulsion system in order to reach an initial 178 by 180-kilometer parking orbit. Roskosmos confirmed the start of the maneuver, but the vehicle likely went out of range of ground station in the Russian Far East before the completion of the firing could be confirmed. Orbital maneuvers
CLICK TO ENLARGE After a period of passive flight around the Earth, Briz-M re-started its engine to stretch its nearly circular orbit to an ellipse with an apogee (highest point) 2,507 kilometers from Earth. (The perigee was increased only slightly to 199 kilometers.) The space tug and its passengers then made a nearly full loop along the transfer orbit, before Briz-M fired its engine for the third time to stretch the orbit even more. Before the Briz-M/Ekspress stack left the range of Russian ground stations, mission controllers had been able to confirm that the third firing had started and the initial parking orbit as well as the first transfer orbit had been within specifications, an industry source told RussianSpaceWeb.com. After the completion of the third burn, Briz-M was programmed to eject an empty external tank. The confirmation of the 3rd burn completion and the subsequent jettisoning of the tank came several hours later, when the vehicle re-appeared within range of Russian ground stations. In the meantime, Briz-M and its passengers completed another passive loop around the Earth, followed by the fourth engine burn, this time consuming propellant from Briz-M's core module. The fourth maneuver was intended to bring the apogee to 53,163 kilometers, while the perigee was to increase only to 408 kilometers. When the stack approached the new apogee, the Briz-M fired for the fifth time, entering a so-called super-synchronous transfer orbit with an apogee of 52,872 kilometers and a perigee of 18,714 kilometers. By climbing to an altitude exceeding 36,000 kilometers, where the satellites will ultimately operate, the upper stage was less bound by our planet's gravitational pull. As a result, Briz-M was able to carry a heavier payload during the energy-hungry fifth maneuver which also tilted the orbital plane of the satellites from 49.3 degrees to nearly matching the equatorial plane. During its ride to orbit, Ekspress-AMU7 was located on top of the two-satellite stack and it separated first from Ekspress-AMU3 nearly 17 hours and 50 minutes after liftoff from Baikonur. It was followed by the separation of Ekspress-AMU3 from the nearly empty Briz-M core module 18 hours and 7 minutes after launch. Shortly thereafter, Briz-M was programmed to use the remnants of its propellant to perform two pre-programmed braking maneuvers, pushing itself into a burial orbit safe from operational satellites. The satellites were to spend nearly two months using their low-thrust electric propulsion systems to reach their operational positions before entering service. Proton's upper stage leaves satellites in out-of-spec orbit Following the separation of two Ekspress satellites from the Briz-M upper stage, Roskosmos announced that the space tug had delivered its passengers to their target orbits. However, a behind-the-scene analysis of the mission's orbital parameters showed that despite very accurate transfer orbits formed by Briz-M, the target orbit specifications fell below planned, an industry source said. Although the out-specifications orbit was not believed to be fatal for the satellites, it would require their flight controllers to improvise some salvage maneuvers in order to get the spacecraft into their operational positions. The initial assessment indicated that the problem might be linked to the manufacturing and calibration history of the propulsion system used aboard Briz-M and that the anomaly might be similar to the one experienced during the launch of Ekspress-AM6 satellite in October 2014. Despite the out-of-specifications release, both satellites successfully reached their operational orbit by the end of March 2022.
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