Russia’s Soyuz rocket carried a Meridian communications satellite to orbit Tuesday morning. The rocket’s Fregat upper stage deployed its payload into an elliptical orbit about 140 minutes after liftoff from the Plesetsk Cosmodrome, which took place at 08:56 Moscow Time (05:56 UTC).
Meridian forms part of the Russian Government’s fleet of communications satellites, operating in elliptical Molniya orbits that enable near-continuous coverage of high northern latitudes. Meridian compliments the geostationary Raduga and Globus communications satellites.
Meridian No.18L is the eighth satellite to be launched for the Meridian system. It is the first of a new batch of four satellites ordered in 2016 to replenish the constellation after a next-generation replacement was delayed.
Following the same design as the earlier Meridian satellites, it is based around a pressurized, three-axis-stabilized bus developed by ISS Reshetnev, likely related to the Uragan-M series of navigation satellites. Each Meridian is designed to operate for at least seven years.
The first Meridian satellite, No.11L, was successfully deployed in December 2006, however by the time of the next satellite’s launch in May 2009 it had ceased to function. The second satellite was placed into too low an orbit after the upper stage of its carrier rocket malfunctioned, although some operation may still have been possible.
Further launches occurred in November 2010, May and December 2011, November 2012 and October 2014. The December 2011 launch failed to reach orbit after an engine problem and apparent explosion affecting the third stage of the Soyuz rocket that had been performing that mission.
The other three satellites ordered in the same block as Meridian No.18L are expected to launch over the next few years. At least one further Meridian launch is scheduled to take place in 2019.
The Molniya orbit that Meridian uses is a particular regime of highly elliptical orbit with a perigee – or low point – relatively close to the Earth and the apogee – its highest point – far above so that the spacecraft takes just under 12 hours to complete a revolution. This period – about half a sidereal day (the time taken for the Earth to rotate on its axis, relative to the stars) – means a satellite can reach apogee twice a day, over the same points on the surface.
Because the orbit is highly elliptical from the ground a satellite would appear to spend most of its time close to apogee, making it easier to track with an antenna. Orbital inclination of about 63.4 degrees places the apogee over the polar regions, but also cancels out perturbations and freezes the apogee and perigee of the orbit relative to the Earth’s surface.
The majority of communications satellites operate in geostationary orbit over the equator, where they remain in fixed positions relative to the surface. At high latitudes, these satellites are so close to the horizon that signals can easily become obstructed or be disrupted by atmospheric or thermal effects. Close to the poles, geostationary satellites may be below the horizon altogether. Satellites in Molniya orbit appear higher in the sky at these latitudes, allowing reliable communications links to be established.
Meridian satellites use orbits with apogees between 38,000 and 39,000 kilometres (23,600 to 24,200 miles, 20,500 to 21,100 nautical miles) and perigees between 1,480 and 2,220 kilometres (920 to 1,370 miles, 800 to 1,190 nautical miles). Tuesday’s launch will have injected Meridian No.18L close to its operational orbit: the satellite will maneuver into its final position under its own power at a later date before it enters service.
The Molniya orbit is named after the Molniya series of satellites developed by the Soviet Union, its name coming from the Russian word for Lightning. Launched between 1964 and 2005, three generations of Molniya satellites were used for multiple forms of communications including telephony, television and military applications. Meridian is the successor to the military aspect of the Molniya constellation.
Molniya also gave its name to the Molniya rocket, a four-stage vehicle derived from Sergei Korolev’s R-7 missile which was used to launch these satellites, as well as early interplanetary probes and US-K missile early warning satellites. An ancestor of the Soyuz rocket that was used for Tuesday’s launch, Molniya continued to fly in its upgraded Molniya-M form until its retirement in 2010.
The Meridian No.18L satellite launched aboard a Soyuz-2-1a rocket with a Fregat-M upper stage. The three-stage Soyuz-2-1a booster is one of three types of Soyuz-2 vehicle, which represent the latest version of Russia’s legendary Soyuz rocket.
First flown in November 1966 Soyuz was an improved version of the Voskhod rocket – itself a three-stage version of Molniya that had been used in the Voskhod human spaceflight program and in support of unmanned reconnaissance missions. Soyuz, Molniya and Voskhod all trace their heritage back to Korolev’s R-7, which in 1957 became the first intercontinental ballistic missile (ICBM) to fly in and – later that year – launched the first satellite, Sputnik.
Upgrades on the Soyuz-2-1a over the previous-generation Soyuz-U included modernized first and second stage engines as well as a new digital flight control system. Its stablemate, Soyuz-2-1b, incorporates a more powerful third stage engine to accommodate heavier payloads, while the smaller Soyuz-2-1v is a heavily modified two-stage version optimized for lighter payloads.
Tuesday’s launch saw Soyuz lift off from Pad 4 at Site 43 of the Plesetsk Cosmodrome in northern Russia. Russia’s main military launch site, Plesetsk’s four Soyuz launch pads were originally built to support testing and operational deployment of R-7A missiles, undergoing conversion for satellite launches after the missile’s retirement.
Site 43/4 is the only one of the four pads currently in service: the nearby Site 43/3 was last used in 2002 but is in the final stages of renovation, while Site 41/1 has been demolished and Site 16/2 was earmarked for a future upgrade and return to operation. Soyuz can also launch from the Baikonur Cosmodrome in Kazakhstan, the Vostochny Cosmodrome in Russia’s far East, and the Centre Spatial Guyanais in Kourou, French Guiana.
All three stages of the Soyuz vehicle burned RG-1 propellant oxidized by liquid oxygen. About sixteen seconds before liftoff the four RD-107A engines of the first stage – and the single RD-108A engine powering the second stage – would have ignited. Over the final seconds of the countdown, these engines built up to full thrust. At the zero-second mark, the launch pad’s swing arms came open and Soyuz climbed away from Plesetsk under the power of the first two stages burning together.
The first stage of Soyuz consisted of four boosters clustered around the second stage, with one engine per booster. These were designated Blok-B, V, G and D, while the second stage was designated Blok-A. Its RD-108A engine featured additional vernier chambers to assist in controlling the rocket’s attitude but was otherwise identical to the first stage RD-107As.
The five engines burned together for about 118 seconds when the first stage burned out and separated. As the boosters separate from the second stage, they vented residual oxygen from the nose to push themselves away from the vehicle, forming a pattern known as the Korolev Cross after the rocket’s chief designer.
After first stage separation, Soyuz’s second stage continued to burn for another 170 seconds. At the end of its burn, the third stage ignited in the normal “fire-in-the-hole” sequence, lighting while the second stage was still firing to keep the propellant settled in its tank.
Exhaust gases from third stage ignition escaped through a lattice structure at the top of the second stage, with separation occurring as soon as the third stage was up and burning. A second and a half later, the top part of the interstage structure separated from the base of the third stage.
The third stage of Soyuz was powered by a single RD-0110 engine. It burned for about four minutes, placing Fregat and Meridian No.18L onto an initial suborbital trajectory. At shutdown Fregat separated and took over, igniting about a minute later for a very short burn to complete insertion into an initial parking orbit. About 36 minutes later Fregat restarted for a ten-minute burn to raise the orbit’s apogee.
After another coast phase, lasting over eighty minutes, a short third burn was made to raise the perigee. With all three burns complete, Meridian No.18L separated from Fregat to begin its mission. Half an hour later Fregat made a final burn to deorbit itself, minimizing debris left in orbit from Tuesday’s mission.
The Fregat-M stage used for Tuesday’s launch was an upgraded version of the original Fregat, powered by an S5.98M engine that burned unsymmetrical dimethylhydrazine and dinitrogen tetroxide.
Tuesday’s launch was the twelfth for a Russian rocket in 2019, coming ten days after the successful launch of the crewed Soyuz MS-13 mission to the International Space Station aboard a Soyuz-FG rocket from Baikonur. Russia’s next Soyuz launch is currently scheduled to take place tomorrow, with a Soyuz-2-1a vehicle carrying the Progress MS-12 cargo spacecraft, also bound for the space station.