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August 17th, 2011 by William Graham
A Proton-M rocket, with the fiftieth Briz-M upper stage, launched Russia’s Ekspress-AM4 communications satellite, after an early morning liftoff from the Baikonur Cosmodrome. However, having launched at 03:25 Thursday local time (21:25 UTC on Wednesday) - and the Proton-M completing its mission successfully – the Briz-M failed to deploy Ekspress-AM4 into a geosynchronous transfer orbit after it was reported to have lost all power at the time during – or shortly after – the fourth burn.
Ekspress-AM4 is the latest in a series of communications satellites operated by the Russian Satellite Communications Company. Developed to replace the earlier Gorizont satellites, the first Ekspress spacecraft was launched in October 1994. Early satellites were built by NPO PM, using the MSS-2500-GSO satellite bus. After the first two satellites, the Ekspress-A series was introduced, consisting of four spacecraft with additional transponders and longer design lives.
Including AM4, eight Ekspress-AM series satellites have been launched since the first flew in 2003. Unlike earlier series, they are not all based around the same bus; the seven already in operation are all MSS-2500-GSOs, however Ekspress-AM4 was built by EADS Astrium around the EuroStar-3000 bus, and future launches will include the Ekspress-1000 and 2000 platforms developed by NPO PM.
A further Ekspress satellite, Ekspress-MD1, was launched in 2009 to provide alternative communication services. A second MD-series spacecraft is expected to launch in December.
With a mass at liftoff of 5,700 kilograms Ekspress-AM4 will be the largest and most powerful satellite in the RSCC’s fleet. It carries sixty three transponders, with thirty operating in the IEEE C band, twenty eight in the Ku band, two in the Ka band, and three in the L band. The satellite is equipped with two solar arrays, which are capable of generating 16 kW of power. Ekspress-AM4 has a design life of fifteen years.
Ekspress-AM4 is the twenty fifth EuroStar-3000 series spacecraft to fly, across all variants. The first, Eutelsat W3A, was launched in 2004. Of the satellites launched, thirteen including Ekspress-AM4 have been in the EuroStar-3000 configuration, three have been in the EuroStar-3000GM configuration, eight have used the EuroStar-3000S variant, and South Korea’s Chollian, or COMS-1, satellite used a modified version.
The Proton-M/Briz-M rocket used to launch Ekspress-AM4 was a four-stage rocket. All four stages were fuelled by hypergolic propellants; unsymmetrical dimethylhydrazine oxidised by dinitrogen tetroxide. Proton was originally developed as the Universal Rocket 500, or UR-500; a huge intercontinental ballistic missile capable of delivering a hundred-megaton nuclear warhead with a range of 10,000 kilometres.
The Universal Rocket series, designed by Vladimir Chelomey, also included the UR-100 missile from which the Rokot and Strela carrier rockets were developed. Several other rockets were planned, including UR-200 which was designed to be versatile enough to operate as a conventional nuclear-armed ballistic missile, a Fractional Orbit Bombardment System missile, and as a launch system for satellites, anti-satellites and manned spaceplanes.
Despite making several successful test flights, the UR-200 was cancelled for political reasons after Nikita Khrushchev was removed from power. Larger rockets, the UR-700 and UR-900, were designed to facilitate manned landings on the Moon and Mars respectively, but were never developed.
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Whilst the UR-500 was never used as a missile, it made four flights in 1965 and 1966; three of which placed N-4 “Proton” satellites into orbit, and the fourth failed to launch another N-4. After launching these spacecraft, the rocket became known as Proton; it was originally intended to have been named Gerkules (Hercules) – a name also suggested for the N1, or Atlantis.
A third stage was added to the UR-500 to produce the Proton-K, which had a far greater payload capacity. The three-stage Proton-K was used to launch Salyut and Almaz space stations, TKS spacecraft, and modules for Mir and the International Space Station.
Sergei Korolev proposed using the Blok-D upper stage under development for the N1 rocket as a fourth stage to launch manned circumlunar missions with Soyuz spacecraft. Although a manned mission was never launched, the Proton-K/Blok-D combination proved successful in launching communications satellites into geosynchronous orbit.
The Proton-K initially had exceptionally poor reliability: in 1969 alone it suffered eight launch failures from ten attempts. As a result it took ten years and sixty one launches to complete its state trials. After a suborbital test flight was conducted in 1970, its success rates began to improve. Today, the Proton-K is still in service; however it is believed to be just one launch away from retirement.
The Proton-M, which has more powerful engines than the Proton-K, and a modernised, digital flight control system, made its first flight on 7 April 2001. The launch of Ekspress-AM4 is the fifty third flight of a Proton-M, and the forty-sixth flight of the Proton-M/Briz-M combination. The Proton-M is the most powerful rocket currently operated by Russia, and is mostly used for launches to geosynchronous orbit.
The first stage of the Proton-M was powered by six RD-276 engines, producing 11 meganewtons of thrust. Around 3.1 seconds before liftoff, the command was given to start the first stage engines, which ignited 1.75 seconds before launch. Fifteen hundredths of a second before launch, the engines were throttled up to full thrust.
At T-0, the Proton-M lifted off from Area 200/39, beginning its climb towards orbit. About sixty five and a half seconds later, it passed through the area of maximum dynamic pressure. The second stage’s four engines ignited 119 seconds into flight, and the first stage was jettisoned 4.4 seconds later.
The second stage was powered by three RD-0210 engines, and one RD-0211 equipped with a gas generator. The stage produced 2.4 meganewtons of thrust, and burned for 211.1 seconds. Around 2.4 seconds before the second stage burned out, the third stage’s RD-0124 vernier engine ignited, and seven tenths of a second after burnout, the second stage was jettisoned.
The third stage’s main engine, an RD-0123, ignited 2.4 seconds after staging, and 10.6 seconds later the payload fairing separated from around the spacecraft. The third stage produced approximately 614 kilonewtons of thrust during the main engine burn, which lasted for about 238.8 seconds. Afterwards, the vernier continued to burn for another 11.9 seconds. One tenth of a second after the vernier engine shut down, the Briz-M separated from the third stage.
The Briz-M upper stage was developed in the 1990s, and first flown on a Proton-K launch on 5 July 1999, which was carrying the Gran No.45L communications satellite. The launch ended in failure before the Briz-M could be tested, after the second stage exploded. The first successful launch of a Briz-M occurred on 6 June 2000, when a Proton-K/Briz-M launched the final Gorizont satellite.
Two further launches were made with Proton-K rockets, both successfully; the AMC-9 communications satellite, and three GLONASS navigation satellites, were launched in 2003. The GLONASS launch is to date the only Briz-M launch which has not targeted either a geosynchronous or geosynchronous transfer orbit. All other GLONASS launches on Proton rockets have been conducted using Blok-DM upper stages; either the Blok DM-2, DM-2M or DM-03, although another launch with a Briz-M is expected to occur later this year.
The remaining forty six Briz-M launches were all made in combination with Proton-M rockets. The first launch occurred on 7 April 2001, carrying a long-obsolete Ekran-M broadcasting satellite. The vast majority of Proton-M/Briz-M rockets since then have carried commercial communications satellites on launches conducted by International Launch Services, however two launches have been made with Raduga-1M military communications satellites, and three flights have deployed Ekspress satellites, which are not considered commercial payloads.
Proton-M/Briz-M rockets have experienced three launch failures; two outright and one partial. One of the outright failures, the launch of JCSAT-11 in September 2007, was caused by the failure of the first stage to separate from the second. The other two failures were due to problems with the Briz-M.
In February 2006, a Proton-M/Briz-M launched Arabsat-4A. The flight profile called for the Briz-M to make three burns, the second of which would last thirty minutes. Towards the end of that burn the Briz-M’s engine cut out about 200 seconds early, leaving the spacecraft in a lower than expected orbit. Unable to raise the satellite to geosynchronous orbit, controllers deorbited it less than a month later.
An investigation determined that the failure had been caused by a blocked oxidiser line, and action was taken to prevent a recurrence. Two years later in March 2008, an identical failure occurred during the launch of AMC-14. In this case the Briz-M shut down 133 seconds before the end of a 32 minute burn. Another investigation was conducted, which discovered that a gas duct had ruptured due to a combination of overheating, pressure fluctuations through the long burn, and erosion. No three-burn missions have been conducted since that failure.
The Briz-M was developed from the Briz-K stage, which was used on the Rokot-K carrier rocket. The Rokot-K has since been replaced by the Rokot-KM, with a modernised Briz-KM upper stage. The core of the Briz-M which contains the engines, propellant tanks, avionics and electronic equipment, is based on the Briz-K. Mounted around the outside of the core is the Auxiliary Propellant Tank, which contains up to 14.6 tonnes of propellant. Fuel is drained from the APT first, and once empty it is jettisoned to reduce the vehicle’s mass.
A single 14D30 engine powers the Briz-M, with four 11D458 vernier engines and twelve 17D58E thrusters being used to provide attitude control. It can make up to eight burns, and produces 19.6 kilonewtons of thrust.
UPDATED – FAILURE:
During the launch of Ekspress-AM4, Briz-M was expected to perform five burns, which is the typical flight profile for a Briz-M placing a spacecraft into geosynchronous transfer orbit.
On a typical mission, the Briz-M would ignite for its first burn about 92 seconds after separating from the third stage. This burn would last about four and a half minutes, completing insertion into a low Earth parking orbit. About 51 minutes later, the second burn would begin as the Briz-M approached the ascending node of its parking orbit, raising the perigee into a new apogee at an altitude of around 5,000 kilometres.
This burn would last around 18.2 minutes, and would be followed by the vehicle coasting for almost a complete revolution, before beginning the third burn about two hours later.
The third burn of a typical mission would last about twelve minutes beginning to raise the orbit’s apogee towards geosynchronous altitudes, and be followed by a two minute coast during which time the Auxiliary Propellant Tank would be jettisoned. It is believed these three burns were successful.
However, a six-minute fourth burn would then be made to raise the apogee further, before entering the longest coast phase of the ascent. This coast would last for around five hours, until the vehicle reaches the apogee of its orbit.
Details in the Russian claim all contact was lost with the stage and spacecraft at either the time of the ignition of the Upper Stage for the fourth burn, or just after the burn was completed - citing a complete loss of power.
The mission was scheduled to carry out a fifth burn at apogee, lasting around seven minutes, to reduce orbital inclination and raise the perigee. Following another coast phase, the spacecraft would have separated from the Briz-M. In all, the ascent would have taken over nine hours to complete, from liftoff to spacecraft separation.
Ekspress-AM4 was launched from Pad 39 of Area 200 at the Baikonur Cosmodrome. One of four Proton launch complexes at Baikonur, Pad 39 has been used for the majority of Proton-M/Briz-M launches, and is overall the most used of the four pads.
The first launch from Pad 39 occurred in February 1980, and since then over 100 launches have been made from it, including the core and three other modules of Mir, three probes to Venus, a probe to Phobos, and the failed Mars-96 mission.
The launch of Ekspress-AM4 is the third flight of a Proton rocket this year. The next launch is planned to occur in a fortnight’s time, when another Proton-M/Briz-M will deploy the first Garpun satellite for the Russian military. However, this is now highly doubtful, as the failure of this mission will likely lead to a Russian commission level investigation.