Spaceflight Insider

Arianespace delivers all-electric SES-15 to GTO on Flight VS17

Soyuz ST-A flight VS17 liftoff

A Soyuz ST-A lifts off from the launch pad in French Guiana. The rocket was carrying the SES-15 communications satellite to geostationary transfer orbit. Photo Credit: Arianespace

French multinational launch provider Arianespace continues to successfully clear its mission backlog induced by the “social movement” in French Guiana earlier in 2017. The company’s Europeanized Soyuz ST-A medium-class rocket took to the skies with the SES-15 communications satellite at 7:54 a.m. EDT (11:54 GMT) May 18, 2017, from the Guiana Space Center in South America.


Unlike other launch vehicles, the Soyuz often appears to take an eternity to leave the pad once the engines are ignited, and Flight VS17 was no different. The rocket’s four strap-on boosters and core stage were ignited 16 seconds before liftoff, requiring nearly 15 seconds for the turbopumps to reach full output.

The Soyuz streaks through the sky with the SES-15 communications satellite. Photo Credit: Arianespace

The Soyuz streaks through the sky with the SES-15 communications satellite. Photo Credit: Arianespace

Once the core stage’s RD-108A engine and the single RD-107A engine in each of the four boosters reached their combined 933,000 pounds-force (4,150 kilonewtons) of sea-level thrust, the hold down arms retracted as the vehicle began its climb from the pad.

Though the SES-15 payload wasn’t a record for a Soyuz geostationary transfer orbit (GTO) mission – that honor goes to the Hispasat 36W-1 launch on Flight VS16 earlier this year – the telecommunications satellite still approaches the upper limit of the ST-A’s capability. The satellite’s 5,075 pounds (2,302 kilograms) accounts for more than 82 percent of the vehicle’s 6,190-pound (2,810-kilogram) capacity to GTO.

The rocket and its payload continued to climb and accelerate as the four boosters and core stage consumed their mixture of liquid oxygen (LOX) and highly refined kerosene (RG-1). Just prior to jettisoning the boosters, the vehicle exceeded the speed of sound (Mach 1) and encountered its greatest aerodynamic loads, also known as “max Q”.

Aerial ballet

Nearly two minutes after lifting off, the four side boosters separated from the core stage after they exhausted their propellant.

As they separated, the boosters appeared to form a cross, performing a flipping and tumbling maneuver as they followed a ballistic trajectory and fell to the Atlantic Ocean below. This aerial display is called the Korolev Cross in homage to Sergei Korolev, the inventor of the R-7 rocket – a precursor to the Soyuz.

After shedding the boosters, the vehicle and its payload continued to accelerate and gain altitude under the power of the core stage’s lone RD-108A engine. Once above a majority of the atmosphere, and no longer needing its protection, the payload fairing was jettisoned approximately 3.5 minutes after liftoff.

Hot staging

The Soyuz’s second stage – or third, depending on how the boosters are classified – began to fire its RD-0110 while still attached to the core stage, an operation known as “hot staging”, and separated approximately 4 minutes, 47 seconds into the flight.

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.

An artist's rendering of the SES-15 satellite. Image Credit: SES

An artist’s rendering of the SES-15 satellite in orbit. Image Credit: SES

Indeed, some other nations who called on the Russian space program for development guidance, or who used it as a basis for their spaceflight program, also use hot staging in some of their launch vehicles.

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, almost 10 minutes after liftoff.

Next stop: GTO

The Fregat was now tasked with completing the delivery of SES-15 to its transfer orbit. To do this, the stage’s S5.92 engine, generating 4,460 pounds-force (19.85 kilonewtons) of thrust, operated for almost 14 minutes.

Following a nearly 4.5-hour coast phase, the Fregat’s engine re-ignited for a final insertion burn lasting a short 52 seconds. The stage, and its still-attached payload, then entered a 20-minute coast, followed by the separation of the SES-15 satellite some 5 hours, 18 minutes after liftoff.

“Fine in a row!” tweeted Stephane Israel, the CEO of Arianespace. “Arianespace keeps up the momentum with its fifth consecutive launch success in 2017. More to come this year!”

Over the next days, SES-15 will unfold its solar panels and deploy its antenna reflectors. It will take about seven months for satellite will slowly raise its orbit with its onboard electric propulsion and will take up its position at 129 degrees West longitude to provide telecommunication services to North and Central America, and the Caribbean.

Flight VS17 marks the fifth successful mission of 2017 for Arianespace, and the first SES payload ever launched on a Soyuz.

Arianespace has a two-week respite before its next mission – the launch of ViaSat 2 and Eutelsat 172B on an Ariane 5 for Flight VA237. That launch is currently set for the opening of a 45-minute window at 7:45 p.m. EDT (23:45 GMT) June 1, 2017.

Video courtesy of Arianespace



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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