Spaceflight Insider

Soyuz rocket successfully delivers EKS-2 early-warning satellite to rare orbit

Soyuz-2.1b / EKS-2 launch

Launch of the Soyuz-2.1b rocket with the EKS-2 satellite from the Plesetsk Cosmodrome on May 25, 2017. Photo Credit: Russian Ministry of Defence

Shortly after 2:34 a.m. EDT (06:34 GMT), May 25, 2017, a Russian Soyuz 2.1b rocket lifted off from site No. 43 at the Plesetsk Cosmodrome and delivered the second of the EKS series of early-warning satellites to a rare Tundra orbit.

EKS-2, designed to detect the infrared and optical signatures of a ballistic missile launch, soared into space atop a Soyuz-2.1b to join its EKS-1 sibling, which was launched 18 months before and will help strengthen the Russian military’s defensive capabilities.


The single RD-107A in each of the four side boosters in the vehicle’s first stage, along with the lone RD-108A in the core, began its ignition sequence several seconds before liftoff. The lengthy power build-up, something endemic to the Soyuz line of launch vehicles, allowed the engines to reach flight speeds and pass health checks before committing to launch.

After the flight computer assessed the performance of the engines, the five power plants spooled-up to a combined 933,020 pounds-force (4,150 kilonewtons) of sea-level thrust and the vehicle lifted off the pad. Once clear of the launch complex, the Soyuz and its military payload turned southeasterly as they began their climb to space.

A small-scale model of the EKS series of early-warning satellites. Photo credit: The Moscow Times

The rocket, consuming a mixture of liquid oxygen (LOX) and highly refined kerosene (RG-1), steadily built velocity and exceeded the speed of sound just before jettisoning the four side boosters.

Aerial acrobatics

Having consumed their supply of LOX and RG-1, the four boosters separated from the core stage nearly two minutes after liftoff.

As they separated, the boosters appeared to form a cross as they performed a flipping and tumbling maneuver. This aerial display is called the Korolev Cross in homage to Sergei Korolev, the inventor of the R-7 rocket – a forerunner to the Soyuz.

After following a ballistic trajectory, the four boosters impacted the ground approximately 217 miles (350 kilometers) from the launch site, roughly near the intersection of the Severnaya Dvina and Vychegda Rivers.

The core (or second) stage’s lone RD-108A continued accelerating the vehicle and payload as they gained altitude. Approximately one minute after booster separation, the protective fairing covering the EKS-2 satellite separated, exposing the satellite to the tenuous, and rapidly thinning, atmosphere.

Hot Staging

The Soyuz’s third stage began firing its RD-0124 while still attached to the core stage, an operation known as “hot staging”, and separated approximately five minutes into the flight.

Although not generally used in U.S. or European launch vehicles, hot staging removes the need for separation motors in the core stage, which decreases the complexity of the staging process. It has been a mainstay of much of the Russian spaceflight industry for 60 years.

The RD-0124, a four-chambered engine fed by a single turbopump, provides 66,200 pounds-force (294.5 kilonewtons) of vacuum thrust and is nearly 10 percent more efficient than the RD-0110 used in other Soyuz variants.

The Soyuz and its payload continued to build speed as the stage burned its LOX and RG-1 propellant for nearly four minutes before the Soyuz’s final stage, the Fregat-MT, separated and ignited more than 9 minutes after liftoff.

Russian orbit for a Russian satellite

The Fregat-MT, outfitted with an S5.95 engine, provided up to 4,460 pounds-force (about 20 kilonewtons) of vacuum thrust over multiple firings to deliver the EKS-2 satellite to its drop-off spot. EKS-2, which has its own propulsion system, will fine-tune its orbit over the coming days to place itself in its desired Tundra orbit.

The Tundra orbit, calculated by Russian engineers, presents a unique ground track, looking like a lopsided “Figure 8”. The geosynchronous, but not geostationary, orbit allows extended loiter times at apogee, providing broad coverage to both high northern and southern latitudes.

The EKS family of satellites make use of this unusual orbit to provide a watchful eye for missile launches from high-latitude areas and augment ground-based radar systems.

The launch of EKS-2 marks the first from Plesetsk, and the third overall (fifth if you count the two for Arianespace in South America), by Russia in 2017.

A Soyuz 2.1b, with the EKS-2 satellite atop, on the launch pad at Plesetsk Cosmodrome

On the launch pad at Plesetsk Cosmodrome stands the Soyuz 2.1b rocket with the EKS-2 satellite atop. Photo Credit: Russian Ministry of Defence


Video courtesy of SciNews



Curt Godwin has been a fan of space exploration for as long as he can remember, keeping his eyes to the skies from an early age. Initially majoring in Nuclear Engineering, Curt later decided that computers would be a more interesting - and safer - career field. He's worked in education technology for more than 20 years, and has been published in industry and peer journals, and is a respected authority on wireless network engineering. Throughout this period of his life, he maintained his love for all things space and has written about his experiences at a variety of NASA events, both on his personal blog and as a freelance media representative.

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