SES-17 & Syracuse 4A | Ariane 5 ECA

Launch Window
(Subject to change)
Oct 24, 2021 – 01:01-03:01 UTC 
Oct 23, 2021 – 22:01-00:01 GFT
Mission Name
SES-17 & Syracuse 4A, Flight VA-255
Launch Provider
(What rocket company is launching it?)
(Who’s paying for this?)
SES S.A. (SES 17)
– DGA (Syracuse 4A)
Ariane 5 ECA (Evolution Cryotechnique type A)
Launch Location
Guiana Space Center, Kourou, French Guiana
Payload mass
SES-17: 6,400 kg (14,000 lb)
Syracuse 4A: 3,500 kg (7700 lb)
Where are the satellites going?
Geostationary Transfer Orbit (GTO)
Will they be attempting to recover the first stage?
No, this is not a capability of Ariane 5
Where will the first stage land?
It will crash into the Atlantic Ocean
Will they be attempting to recover the fairings?
No, this is not a capability of Ariane 5
Are these fairings new?
How’s the weather looking?
This will be the:
– 111th launch of Ariane 5, ever
– 2nd launch of Ariane 5 in 2021

10th launch for Arianespace in 2021
– 102nd orbital launch attempt of 2021
– 313th launch of any rocket from the Guiana Space Center
Where to watch
Livestream (not official)

What Does All This Mean?

Arianespace will be launching two large satellites, SES-17 and Syracuse 4A, to a Geostationary Transfer Orbit (GTO). They will be launching on board an Ariane 5 ECA rocket from the Guiana Space Center in Kourou, French Guiana. The flight designation is VA 255.

After launch, the satellites will raise their orbits to a Geostationary Earth Orbit (GEO) using their own propulsion over an extended period of time. SES-17 will station itself over the Americas, the Caribbean, and the Atlantic Ocean.

This is the last Ariane 5 launch before the upcoming James Webb Space Telescope mission, scheduled for December 18, 2021.

What Is SES-17?

SES-17 is the largest GEO satellite built for SES, and also the largest such satellite ever built by Thales Alenia Space. It is designed to work together with other satellites from the Medium Earth Orbit (MEO) constellation known as O3b mPOWER. SES-17 will provide mobile internet services to passenger aircraft over the Americas and the Atlantic Ocean.

Both SES-17 and O3b mPOWER satellites make use of a novel software system called Adaptive Resource Control (ARC). ARC will provide dynamic management of service requests and available resources in orbit and on the ground. SES has been working on ARC with Kythera Space Solutions since September 2019 when they jointly announced the development.

SES-17, Thales Alenia Space, Arianespace, Ariane 5
SES-17 in the Compact Antenna Test Range (CATR). (Credit: Thales Alenia Space)

What Is Syracuse 4A?

Syracuse 4A is the first in a set of two military communication satellites in the Syracuse 4 (formerly Comsat NG) program. These will extend the French fleet of military communication satellites, which currently consists of Syracuse 3A and 3B satellites (wholly owned by France) and the Sicral 2 and Athena-Fidus satellites, which are jointly owned by France and Italy.

The Syracuse 4 satellites are needed in order to handle additional communication demands from un-crewed aerial platforms (drone aircraft) and other military aircraft.

Syracuse 4, Airbus, Arianespace, Ariane 5
Syracuse 4 satellite. (Credit: Airbus)

What Is Ariane 5 ECA?

Ariane 5 ECA (Evolved Cryogenic, model A) is the heavy lift workhorse of Arianespace. It is capable of lofting over 10 tonnes of payload to GTO. This includes any deployment equipment and payload adapters. When launching dual payloads, such as for this mission, its take-off mass is 780 tonnes.

Ariane 5 is a two-stage liquid-fueled rocket, assisted by twin solid rocket motors at lift-off. Due to its heavy lift capabilities, it can be used for missions that send payloads beyond Earth orbit, such as Rosetta in 2004, BepiColombo in 2018, and the James Webb Space Telescope later in 2021.

Ariane 5, schematic, Arianespace
Ariane V rocket with cut-away upper stage and payload fairing. (Credit: ESA)

Solid Rocket Boosters

Known as Etage d’Accélération à Poudre (EAP, powder acceleration stage), these solid propellant boosters are the largest such motors ever produced in Europe. Each booster is 31 m (~102 ft) long with a 3 m (~10 ft) diameter. With a dry mass of 37 tonnes (~82,000 lb), each one can hold 238 tonnes of propellant prior to launch.

The boosters are constructed from three segments of steel casing each containing propellant. The upper segment is filled with 23.5 tonnes in Italy prior to transport to the launch site. The other two segments, however, are loaded with propellant on site at the Guiana Space Center. The middle segment contains 107.5 tonnes, whereas the bottom segment hold 107 tonnes.

The propellant used consists of three main elements:

  • ammonium perchlorate (acting as the oxidiser)
  • aluminum powder (in the role of chemical reducer)
  • polybutadiene (acting as binding agent and also a catalyser)

Cryogenic Core Stage

Known as Etage Principal Cryotechnique (EPC, main cryogenic stage), this liquid-fueled rocket stage runs on liquid hydrogen (LH2) and liquid oxygen (LOx). At its base is the single Vulcain 2 engine, which fires for more than 9 minutes of flight time.

The stage is 30 m (~100 ft) long, with a 5.4 m (~18 ft) diameter. At take-off the stage holds 25 tonnes of liquid hydrogen and 150 tonnes of liquid oxygen. The difference in mass is due to the difference in atomic mass of hydrogen and oxygen, with hydrogen being the lightest element in the periodic table.

The Vulcain 2 engine is ignited at T-0 with the rocket firmly held down by the launch clamps. It builds to normal thrust levels over several seconds before the solid boosters are ignited and the clamps are released. This is very different from SpaceX’ Falcon 9, for example, for which first stage ignition is started at around T-3 seconds, and T-0 represents time of launch.

Ariane 5, center stage, booster, pad, Arianespace
Vulcain 2 core stage engine, with solid boosters on either side. (Credit: ESA)

Upper Stage

Known as Etage Supérieur Cryotechnique de type A (ESC-A, improved cryogenic stage, type A), the upper stage also runs on LH2 and LOx. It uses the same HM7B engine that was previously flown on Ariane 4’s third stage. The stage holds a combined propellant mass of 14.7 tonnes (~32,400 lb).

Above the propulsion stage, the Vehicle Equipment Bay contains all the avionics and guidance control for the entire vehicle. It also houses the telemetry systems used to transmit all monitored parameters back to the ground. At the top of the Vehicle Equipment Bay is the payload adapter.

Ariane 5, Arianespace, upper stage
Upper composite of second stage, VEB, and supporting structure. (Credit: ESA)

Payload Support Equipment

At launch, the payload is protected within the payload fairing, which consists of two halves. The fairing has the same diameter as the core and upper stages of 5.4 m, and is 17 m long. The fairing is discarded after 3 minutes onto the flight, at an altitude no lower than 100 km.

On dual satellite launch missions, such as this one, the payloads are supported and housed within the Système de Lancement Double Ariane 5, or Sylda 5. This structure has a diameter of 4.6 m and can be configured for any height between 4.9 m and 6.4 m, in 0.3 m increments.

Typical Launch Sequence For GTO Orbital Flights

Time (w.r.t. T-0)Key EventsAltitude (km)
0:00:00Vulcain 2 ignition0
0:00:07Solid rocket boost ignition + lift-off0
0:02:23Booster separation69
0:03:11Fairing deployment107
0:09:01Core stage shutdown and staging178
0:24:47Upper stage shutdown640
0:27:25Deployment of 1st satellite1,036
0:29:41Sylda deployment1,456
0:34:47Deployment of 2nd satellite2,585
0:49:36End of Ariane 5 mission6,340

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