Soyuz 2-1b launches latest GLONASS satellite – returns Plesetsk pad to service

Russia has launched a new satellite to replenish its GLONASS navigation system Tuesday, via a Soyuz-2-1b rocket with a Fregat-M upper stage. The launch took place at 11:54 Moscow Time (08:54 UTC), returning to service a launch pad at the Plesetsk Cosmodrome that has stood dormant for over seventeen years.

GLONASS is a network of navigation satellites originally developed by the Soviet Union and now maintained by Russia. It is similar in concept and purpose to the US Global Positioning System (GPS) or European Galileo system, and like those projects uses a fleet of spacecraft in medium Earth orbit to broadcast precise timing signals that a receiver can use to triangulate a location on the Earth’s surface.

The name GLONASS comes from the Russian Глобальная навигационная спутниковая система (Globalnaya Navigatsionnaya Sputnikovaya Sistema), meaning Global Navigation Satellite System, while the individual satellites are named Uragan, meaning Hurricane.

Satellite navigation relies on knowing how long signals from a satellite have taken to reach a receiver and using this to calculate the distance back to the satellite. In addition to the time, satellites broadcast orbital parameters that can be used to determine their positions in orbit. By computing how far a signal could travel from each satellite in the time calculated, and intersecting the results, the receiver can work out its location. Signals from four satellites are needed to determine a position, although additional signals can also be used to provide a more accurate fix.

To ensure accurate timing signals, GLONASS satellites are equipped with caesium atomic clocks. Each spacecraft broadcasts L1 and L2 navigation signals for both civilian and military uses. L1 signals are broadcast on frequencies around 1,602 megahertz – with different satellites operating on slightly different frequencies depending on their assigned channel. L2 signals vary similarly between satellites, but are at lower frequencies around 1,246 megahertz. The civilian signals are open and unrestricted – they can be used by any compatible receiver – and are named L1OF and L2OF. Corresponding secure signals, L1SF and L2SF, are encrypted for military users and provide greater precision.

Glonass diagram via ESA

GLONASS relies on a constellation of twenty-four satellites to provide a continuous worldwide navigation service, although it can provide continuous coverage of Russia with just eighteen satellites operational. The spacecraft are arranged into three planes with eight satellites per plane. GLONASS satellites orbit 19,100 kilometers (11,900 miles, 10,300 nautical miles) above the Earth, with their orbits inclined at 64.8 degrees to the equator.

As well as providing Russia with an independent navigation capability, GLONASS can be used in conjunction with other navigation systems. Modern receivers can use satellites from several different constellations to get the most accurate fix on their position. Because GLONASS uses a more highly-inclined orbit than GPS, Galileo or other navigation satellites, it provides better coverage of polar regions than the other systems.

The Soviet Union began developing GLONASS in the 1970s, with the first satellite – Kosmos 1413 – launching in October 1982. The constellation was built up through the 1980s with launches of two or three satellites at a time aboard Proton-K rockets with Blok DM-2 upper stages. When the Soviet Union was dissolved in December 1991, GLONASS came under the control of the Russian government. In 1993 the system became operational for users in Russia, with additional launches over the next three years allowing worldwide service to start in 1996.

The first-generation Uragan spacecraft were only designed to operate for three years, launching in groups of up to three aboard Proton rockets. This short lifespan led to problems for GLONASS in the late 1990s, as not long after the system became operational older satellites began to fail at a faster rate than they could be replaced. The constellation fell into disrepair and by 2001 fewer than ten spacecraft remained in service.

In 1999 Russia’s President, Boris Yeltsin, decreed that the GLONASS system be brought back into operation and upgraded. In recent years, Vladimir Putin’s personal interest in the project has renewed focus on the program’s future.

Tuesday’s launch carried Uragan-M No.759, a second-generation GLONASS satellite. The Uragan-M series was introduced from 2001, increasing the satellites’ lifespan from three to seven years and introducing new capabilities including the L2OF signal. Initial launches continued to be made in groups of three atop Proton rockets, with smaller Soyuz-2-1b/Fregat vehicles later being used to carry out replenishment launches with individual satellites. Several satellites are kept in launch-ready condition on the ground, to be called up at a few months’ notice when required. Uragan-M No.759 was called up in September for Tuesday’s launch aboard Soyuz.

The Uragan-M spacecraft are built by ISS Reshetnev, formerly known as NPO PM, around a pressurized bus developed for the program. Each satellite has a mass of about 1,415 kilograms (3,120 lb) and incorporates three-axis stabilization and twin solar arrays to generate power. Although the design life of an Uragan-M is seven years, most of the satellites have far exceeded this.

Uragan-M No.759 will replace its sister satellite Uragan-M No.717, also known as Kosmos 2426, in the second plane of the GLONASS constellation. Kosmos 2426 was one of three satellites launched aboard a Proton rocket on 25 December 2006, entering service in April 2007. Kosmos 2426 is the oldest GLONASS satellite still in operation, although it was taken out of front-line service in August and placed into a maintenance status. Kosmos 2425 (Uragan-M No.716), which was launched on the same rocket as Kosmos 2426 but commissioned several months later, also remains in service as an on-orbit spare.

Once it is deployed into orbit, Uragan-M No.759 will receive a new name under the Kosmos series used to identify most Russian military satellites. Kosmos designations are assigned sequentially, with Uragan-M No.759 expected to become Kosmos 2544.

A third generation of GLONASS satellites, Uragan-K, is currently under development. Experimental Uragan-K1 spacecraft were launched in 2011 and 2014, with operational launches expected to begin next year. After several initial launches the Uragan-K1 will be superseded by the further-upgraded Uragan-K2.

Tuesday’s launch used a Soyuz-2-1b rocket with a Fregat-M upper stage. This combined the three-stage Soyuz booster with the restartable Fregat-M, which can deploy its payload directly into medium Earth orbit. Soyuz lifted off from Pad 3 of Site 43 at the Plesetsk Cosmodrome in northern Russia. Tuesday’s mission is the first launch in over seventeen years to fly from this pad, which sustained damage during a 2002 launch failure and has only just been returned to service.

Soyuz 2-1b rocket – via Roscosmos

Site 43 is one of the oldest launch complexes at Plesetsk, having initially entered service in 1961 to support operational deployment of the R-7A missile. It contains two of the four R-7 launch pads built at Plesetsk, with the other pads built earlier at Sites 41/1 and 16/2. While R-7’s service as a missile was brief, it became the basis for one of the most successful series of carrier rockets ever developed, and the Soyuz-2-1b that will make Tuesday’s launch is descended from it. All of the R-7’s launch pads at Plesetsk were later used for orbital launches particularly in support of Soviet military programs.

Both pads at Site 43 were taken out of service as a missile launch site in 1968, when the obsolete R-7A was removed from the Soviet Union’s missile arsenal. The following year Pad 4 was recommissioned for orbital launches of Voskhod and Molniya-M rockets, both derived from the R-7. Pad 3 – which had not seen a launch in its time as a missile complex – was first used on 18 February 1971 for a Voskhod launch carrying Kosmos 396, a Zenit-4M reconnaissance satellite. Pad 3 was initially only used by Voskhod vehicles.

On 18 May 1973, Site 43/3 was the venue for the maiden launch of a new rocket developed from the R-7 family, the Soyuz 11A511U. Also known as Soyuz-U, this upgraded the original Soyuz design – itself derived from Voskhod – with enhancements from the Molniya line of rockets that had been spun off years before. This was intended as a universal replacement for several other rockets, including Voskhod and Soyuz. Soyuz-U would go on to become the most-flown orbit-going rocket ever developed, making over 780 launches by the time of its retirement in 2017.

In 1975 a period of maintenance at Pad 4 saw the first Molniya-M launches from Pad 3, with Molynia-2 and 3 series communications satellites aboard. As Pad 4’s downtime continued into 1976 Pad 3 was also used for a Vostok-2M launch, deploying a Meteor-Priroda remote sensing satellite. Even after Pad 4 returned to service, launches of these classes of rockets continued to be made occasionally from Pad 3, however, the majority of activity remained deployment of Zenit and Yantar reconnaissance satellites by Voskhod and Soyuz-U vehicles. Plesetsk’s last Voskhod launch took place from Pad 3 in June 1976.

Pad 4 was heavily damaged in March 1980 when a Vostok-2M rocket exploded during fuelling operations. The launch pad was out of service for three years while repairs were conducted, resulting in more launches from Pad 3 during this time. A few years later, in 1987, a Soyuz-U launch failure damaged Pad 3, which took it offline for eighteen months.

Through the 1980s, 1990s and into the early 2000s, Soyuz-U and Molniya-M rockets continued to fly from Pad 3. The majority of these launches deployed military satellites, however, a small number of the Soyuz-U missions carried Bion and Foton research satellites, derived from the Vostok spacecraft and Zenit spy satellite with a recoverable capsule for biological and microgravity research respectively. On 15 October 2002, a Soyuz-U rocket was tasked with deploying an upgraded version of the Foton spacecraft, Foton-M No.1.

Foton-M No.1 was a joint venture between the Russian Federal Space Agency and the European Space Agency, carrying an international complement of scientific experiments to be conducted in microgravity. At the end of its mission, the spacecraft would have been deorbited, and its capsule recovered. Foton-M No.1 would never reach orbit. About twenty seconds after lifting off from Site 43/3, one of the rocket’s four boosters detached and came down close to the launch pad. The rest of the rocket fell back to Earth about one kilometer (1,090 yards) further downrange.

A Russian Army soldier, Private Ivan Marchenko, was killed by a window frame which collapsed in a building close to the launch pad, while eight others were injured in the accident. The damage sustained at Pad 3 took the facility out of service and with Pad 4 also unavailable due to renovation work, Plesetsk was left with Site 16/2 as its only operational complex for the Soyuz and Molniya. The renovation of Pad 4, necessary to support the development of the new Soyuz-2 rocket, delayed efforts to repair Pad 3. Site 43/4 returned to service in 2004 with a suborbital test of the Soyuz-2-1a rocket.

The renovation of Site 43/3 includes the changes that were made at Pad 4 to support Soyuz-2 launches, since the Soyuz-U and Molniya-M that previously flew from Pad 3 have both been retired in the seventeen years since the complex was last used. Bringing the second pad back online will allow an increased flight rate for Soyuz from Plesetsk, while also providing a backup should either pad require maintenance or repair. Tuesday’s launch will be the 219th to take place from Site Pad 3.

The twin launch pads at Site 43 are now the only operational Soyuz launch complexes at Plesetsk: Site 41/1 was last used in September 1989 and has since been dismantled, while Site 16/2 has not been upgraded to handle Soyuz-2. Its last launch took place in May 2012, with the last Soyuz-U rocket to fly from Russia’s northern Cosmodrome. The pad was reportedly due to be renovated once work Site 43/3 was complete, to become a dedicated pad for the smaller Soyuz-2-1v rocket, however it is unclear whether this is still planned, or when it is likely to be completed.

Soyuz also has operational launch complexes at Site 31/6 of the Baikonur Cosmodrome, Site 1S at the Vostochny Cosmodrome and the Ensemble de Lancement Soyouz (ELS) at the Centre Spatial Guyanais in Kourou, French Guiana. The ELS site is used exclusively for commercial launches conducted by Arianespace. An additional launch pad, Site 1/5 at Baikonur, was formerly operational but has not been upgraded for Soyuz-2 missions. It went out of service following the final Soyuz-FG launch earlier this year. At this stage, it remains unclear whether Pad 1/5 will be renovated and returned to service.

Tuesday’s launch used a Soyuz-2-1b rocket with a Fregat-M upper stage. This combined the three-stage Soyuz booster with the restartable Fregat-M, which can deploy its payload directly into medium Earth orbit

The Soyuz-2-1b is currently the most advanced evolution of the R-7 missile, which was originally designed by Sergei Korolev in the 1950s. The Soyuz-2-1b is one of three modernized Soyuz-2 versions, the first of which was introduced in 2004. The Soyuz-2-1a incorporates several enhancements over the previous-generation Soyuz-U, including upgraded first and second stage engines and a new digital flight control system. Soyuz-2-1b incorporates the same modifications, as well as a redesigned third stage with an RD-0124 engine, allowing it to deliver heavier payloads into orbit. The smaller Soyuz-2-1v is optimized for smaller payloads, based around the second and third stages of the Soyuz-2-1b.

Fregat upper stages have been used in conjunction with the Soyuz rocket since 2000, facilitating missions that require precise orbital insertion, injection into higher orbits than Soyuz can reach on its own, or missions that require several satellites to be deployed into different orbits.

Fregat Upper Stage – via ESA

Fregat has allowed Soyuz-2 to replace the Molniya series of rockets as well as Soyuz-U and has opened the door to commercial Soyuz launches targeting sun-synchronous and geosynchronous transfer orbits. For Tuesday’s launch, Fregat is being used to insert Uragan-M No.759 directly into its operational medium Earth orbit.

Soyuz has a lengthy ignition process, with the first and second stage engines lighting about sixteen seconds before the rocket was due to lift off, building up to full thrust as the countdown reached zero. The first stage consisted of four strap-on boosters, each powered by an RD-107A engine with four combustion chambers and nozzles. In the center, the second stage had a single RD-108A, with four main chambers and four additional verniers for attitude control. The first, second and third stages of Soyuz all burn RG-1 propellant – a refined form of kerosene – oxidized by liquid oxygen.

Once the engines had built up thrust, Soyuz was released from Pad [43/3], with arms swinging open and allowing the rocket to begin its ascent. For the first 118 seconds of its flight both the first and second stages fired, before the first stage exhausted its propellant. At this point the spent first stage boosters were jettisoned, venting residual oxidizer to push them away from the rocket and prevent any recontact with the second stage.

With the first stage separated, Soyuz’s second stage continued to fire for another 170 seconds. At the end of second stage flight the third stage’s RD-0124 engine ignited in a “fire-in-the-hole” staging technique, where the third stage lit up with the second stage still burning. Soyuz is designed to separate its second and third stages in this way to ensure propellant in the third stage remains settled in its tanks, without the need for additional ullage motors. The interstage between Soyuz’s second and third stages is a lattice structure, which allowed exhaust gases to escape before separation occurred. The third stage burned for between four and five minutes. Soyuz’s payload fairing would have separated from the nose of the rocket late in the second stage burn, or early in third-stage flight.

Shortly after the third stage ended its burn, Fregat-M separated to carry Uragan-M No.759 the rest of the way to its planned orbit. Fregat uses storable propellant – unsymmetrical dimethylhydrazine and dinitrogen tetroxide – and is equipped with an S5.98M engine which can be restarted multiple times. Tuesday’s launch calls for it to make three burns. The first of these was performed shortly after separation to establish an initial parking orbit. Over the next three and a half hours, two further burns will be made to raise Fregat’s orbit ahead of payload deployment.

Friday’s launch is the second Soyuz launch in four days, following a successful Soyuz-2-1a mission from the Baikonur Cosmodrome on Friday which deployed the Progress MS-13 spacecraft. The next Soyuz launch is scheduled for 17 December out of the Centre Spatial Guyanais in French Guiana.

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