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Proton-M succeeds in a cliff-hanger mission Sporting the latest round of modifications known as Phase IV, a Proton-M rocket boosted the exceptionally heavy Intelsat-31 communications satellite on June 9, during the third mission in 2016 for Russia's commercial workhorse. The rocket's Briz-M stage successfully completed the mission despite an apparent anomaly during the operation of the second stage Proton lifts off with the Intelsat-31 satellite on June 9, 2016. Credit: Roskosmos Intelsat-31 (DLA-2) mission at a glance:
Intelsat-31 (DLA-2)
The Intelsat-31 communications satellite built by Space Systems Loral, with the primary purpose of hosting the DLA-2 payload for London-based Intelsat company. The satellite was designed to provide in-orbit backup for the DirecTV Latin America Direct-to-Home, DTH, television platform, a leading DTH digital television services operator in Latin America. The C-band transponder payload on Intelsat-31 was designed for Intelsat's own communications infrastructure in Latin America, as well as for DirecTV services in Latin America. In the meantime, Ku-band transponders was to be used to expand its current DTH entertainment offerings for Pan Americana and provide backup and restoration services. Upon entering space, Intelsat-31 was to be co-located in a geostationary orbit 36,000 kilometers above the Equator at 95 degrees West longitude along with the Intelsat-30 (DLA-1) and Galaxy-3C satellites. There, it could augment and provide redundancy and reliability for broadcast services in Latin America. The satellite with a total power capacity of 20 kilowatts can be used by DirecTV Latin America for high definition programming in nine different countries. Intelsat-31 (DLA-2) specifications:
Basic design of Space Systems/Loral 1300 platform. Credit: SSL
Road to the launch pad
The Intelsat-31 satellite during pre-launch processing in Baikonur on May 27, 2016. The contract for the launch of the Intelsat-31 (DLA-2) satellite on a Proton rocket was signed in March 2013. It was to be the 11th Proton mission delivering spacecraft for Intelsat and the 5th launch to support DirecTV. As of beginning of 2014, Intelsat-31 was under construction by Space Systems/Loral of Palo Alto, California, based on the company's flight proven 1300 platform. The agreement for the launch was announced by the International Launch Services, ILS, on Jan. 14, 2014. It was the first launch assignment from Intelsat for one of two missions that the organization preliminary booked on Proton in March 2013. As of end 2014, the mission was expected in October or November 2015. After the delay of the ExoMars-2016 launch in September 2015, from January to March 2016, the launch of Intelsat was considered either at the end of January or in April 2016. Around March 2016, the mission was postponed until May 17 and it was later rescheduled for May 28, 2016. On May 19, GKNPTs Khrunichev announced that the launch would have to be postponed due to technical reasons discovered during pre-launch checks. No new launch date was announced at the time, but by May 25, the launch was scheduled for June 8. As it transpired, a replacement component had to be shipped to Baikonur to complete the repairs. On June 3, the fully assembled Proton rocket left Hall 111 inside Facility 92A-50 for a short trip by rail to an outdoor fueling station of the Briz-M upper stage. Due to hazardous nature of the operation and its proximity to Building 92A-50, the facility was cleared of non-essential personnel, an ILS representative said. The rocket spent two days at the Briz fueling station before rolling straight to its launch pad No. 24 at Site 81 on June 5, 2016.
Proton with Intelsat-31 is erected onto launch pad on June 5, 2016. Intelsat-31 launch profile
Proton-M Phase IV to carry Intelsat-31 into the super-synchronous orbit With its mass of 6.45 tons, the Intelsat-31 satellite was a suitable payload for the first flight of the Phase IV upgrade of the Proton-M rocket. However even this most powerful version still needed a special flight profile, which is only occasionally used to deliver its heaviest payloads. Rather than releasing its cargo into a Geostationary Transfer Orbit, GTO, the Proton's Briz-M upper stage will boost Intelsat-31 into a so-called Supersynchronous Transfer Orbit, SSTO. Climbing to an altitude exceeding 65,000 kilometers above the Earth's surface, or almost twice as high as the target orbit, the Briz-M will be less bound by our planet's gravitational pull than it would be at its usual destination. As a result, the space tug will be able to carry around 200 kilograms of extra cargo during an energy hungry maneuver, which will tilt the orbital plane of the satellite from the latitude of the Baikonur Cosmodrome in Kazakhstan closer to the equatorial plane. The Intelsat-31 launch will originate from Pad 24 at Site 81 in Baikonur. The primary pad No. 39 at Site 200, which would normally be used for commercial missions, was under repair at the time of this launch campaign. The liftoff of the Proton-M rocket with a Briz-M upper stage was originally scheduled for June 8, 2016, at 10:10:00 Moscow Time (3:10 a.m. EDT). However around three hours before the planned launch time, the International Launch Services, ILS, and Roskosmos announced that the mission had been postponed "due to an issue associated with electrical ground system equipment at Launch Pad 24." According to ILS, "the issue has been identified, equipment has been replaced and verification of all associated cabling and connectors was in work. The Proton launch vehicle and the Intelsat-31 satellite were unaffected and remained in a safe configuration at the launch site." "Pending a successful outcome of the cable and connector verifications," another launch attempt would be made 24 hours later, on June 9, 2016, at 10:10 Moscow Time, Roskosmos said. Several hours later, ILS announced that following the additional verifications of the cables and connectors associated with last night’s issue which resulted in a delay to the Intelsat 31 launch, the problem has been isolated to a connector on the flight vehicle. The ground system was wrongly identified as the cause of today’s delay. The flight connector issue has been resolved and the vehicle cleared for flight still 24 hours after the original launch time. After a 24-hour delay, the Proton-M rocket carrying Intelsat-31 lifted off on June 9, 2016, at 10:10:00.019 Moscow Time (3:10 a.m. EDT). According to a flight program, after a few seconds in vertical flight, the launch vehicle began heading east and slightly north to align with an orbital inclination of 51.5 degrees. The rocket passed the maximum dynamic pressure of the atmosphere 62 seconds into the flight. The Proton's first stage separated two minutes after the liftoff, but moments earlier, the second stage began to fire its engines through the lattice structure connecting the two boosters. The second stage continued firing until five minutes 26 seconds into the flight and then separated with the help of small solid motors firing against the direction of the flight. During the operation of the third stage, the payload fairing split in two halves and dropped away five minutes 46 seconds after the liftoff. The third stage completed its work and separated nine minutes and 41 seconds into the flight. At that point, the payload section, including the Briz-M upper stage and the satellite, was on a suborbital trajectory, just short of an orbital velocity. Around a minute and a half after the separation, Briz-M initiated its first engine firing lasting four minutes 17 seconds to reach an initial parking orbit at an altitude of around 173 kilometers. Roskosmos and ILS confirmed that maneuver had been completed successfully, however data from a ballistic center monitoring the mission indicated that the main engine on Briz-M had fired 34.57 seconds longer than planned. It was not immediately clear whether that deviation had represented a serious technical problem. At the same time, the telemetry indicated that the third stage had fallen short 28.2 meters per second in velocity by the time it had completed its firing.
The telemetry from the launch shows that the third stage developed a velocity of 7,279.5 meters per second instead of required 7,307.7 meters per second. Credit: GKNPTs Khrunichev / Novosti Kosmonavtiki In the meantime, multiple data from the operation of the second stage also showed abnormal performance, quickly making it the most likely source of a subsequent problem with the operation of the third stage. The telemetry from the flight indicated that one of four engines of the second stage was shut down nine seconds earlier than scheduled. Fortunately, three remaining engines were able to keep the rocket largely on track. The telemetry also showed that after the separation, the second stage impacted the ground short of its nominal impact area, clearly as a result of an anomaly during the flight.
The telemetry indicated that the engine responsible for the yaw axis of the rocket apparently shut down prematurely leading to a 1.7-degree deviation from the correct yaw angle around the time of separation between the second and third stage. Fortunately, all four engines on the stage can gimbal (pivot) up to 3 degrees and 15 minutes along one axis, which was enough to compensate for the asymmetrical thrust. Click to enlarge. Credit: GKNPTs Khrunichev
The second stage of the Proton rocket fell short of the nominal impact site, likely as a result of an anomaly in the propulsion system. Credit: GKNPTs Khrunichev Briz-M successfully completes orbital insertion After making an almost full revolution around the planet, less than an hour and a half later, Briz-M was to fire its engine again for less than 20 minutes to boost the apogee (highest point) of its orbit to 6,000 kilometers. ILS confirmed that maneuver as successful. After a more than two hours of unpowered flight, Briz-M was to perform two more engine burns, this time to raise the apogee to more than 65,000 kilometers from Earth. Since the external tank of the Briz-M stage nominally runs out of propellant in the middle of an almost 18-minute maneuver, the engine firing is split into two burns separated by the jettisoning of the empty tank. During the second half of the dual maneuver, the engine consumed propellant from Briz-M's remaining core tanks. The stack was then expected to climb passively for 10.5 hours to its supersynchronous altitude. The results of the maneuver would not be known for another six hours until the Briz would enter the range of Russian ground stations. However, data from the US Joint Space Operations Center indicated that the external tank from the Briz-M was dropped in a close to nominal 360 by 14,030-kilometer orbit with an inclination 50.8 degrees toward the Equator. Around 20:00 Moscow Time on June 9, Briz-M/Intelsat-31 stack reentered the range of Russian ground stations, which confirmed that the third and fourth firing of the space tug had been normal. At the end of the fourth maneuver, Briz-M fired extra 12.55 seconds. Upon reaching the apogee, Briz-M ignited its main engine for three minutes to enter a super-synchronous transfer orbit. The same maneuver also reduced the orbital inclination from 50.5 degrees to 29.6 degrees toward the Equator. After Briz-M had taken right position in space and began to spin, Intelsat-31 separated from its space tug into a 3,503 by 65,000-kilometer orbit still inclined 29.6 degrees toward the Equator. Around 01:30 Moscow Time on June 10 (6:30 p.m. EDT on June 9), ILS confirmed that Briz-M had performed its fifth engine firing as planned. The separation was scheduled to take place less than 13 minutes after the completion of the fifth maneuver and 15 hours 31 minutes after the liftoff from Baikonur. The operation actually took place just 20 seconds off the scheduled time, successfully concluding the mission at 01:40:40 Moscow Time on June 10, 2016. Briz-M was then to use its remaining propellant to maneuver to a burial orbit with two burns of attitude-control thrusters, SOZ, which were scheduled between 04:50 and 06:20 Moscow Time on June 10, 2016. There, all its pressurized contents were to be vented into space to reduce the possibility of an explosion and the proliferation of space junk. In the meantime, Intelsat-31 was to use its own electric propulsion system to match its orbital inclination to that of the equatorial plane and to raise its perigee and reduce its apogee to a circular orbit 36,000 kilometers above the Equator. Investigation into the close call Following the successful release of the Intelsat-31 satellite, Russia formed an accident commission to investigate the circumstances of a close call during the operation of the second stage's propulsion system and to develop corrective actions as necessary. According to industry sources, the problem was eventually traced to the breakdown of one of the propellant lines leading to the engine's turbo-pump, apparently as a result of the pipe's inadequate attachment and excessive pump loads.
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Click to enlarge.
Click to enlarge.
The propulsion section of the Proton's first stage at the impact site. Click to enlarge. |
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