Technical features

Cutaway view of Ariane 5 ECA. Credits: Arianespace

Lower composite

The lower composite comprises:

• Two EAP solid-rocket boosters each 31.6 metres tall and 3 metres in diameter, with an empty mass of 37 tonnes plus 240 tonnes of solid propellant. They deliver 7,000 kN (700 tonnes) of thrust in vacuum, just over 90% of the total thrust of the launcher at lift-off. After burning for 2 minutes and 10 seconds, the EAPs separate from the core stage 60 km above the Atlantic Ocean.

• An EPC cryogenic core stage, which burns cryogenic propellants combining liquid hydrogen and oxygen. Standing 30 metres tall, it weighs 12.5 tonnes empty and carries 174 tonnes of propellant: 149 tonnes of liquid oxygen on top and 25 tonnes of liquid hydrogen below. It operates for 9 minutes, before separating from the upper stage at an altitude of around 145 km. Its Vulcain engine, designed by Snecma Moteurs, weighs 1,650 kg and delivers 20 times more thrust than Ariane 4’s. Vulcain 2 is an upgraded version of this engine, designed for Ariane 5 ECA, providing a 20% performance gain to deliver 1,390 kN (139 tonnes) of thrust in vacuum.

Upper composite

The upper composite separates from the core stage at around 145 kilometres to impart the velocity required to inject the payload into geostationary transfer orbit (GTO). It comprises the only stage that is not ignited at lift-off. The type of stage depends on the launcher variant.

Vehicle equipment bay (VEB): this is the launcher’s electronic brain, containing all the instructions necessary for flight; it controls and corrects the launcher’s position if needed, commands engine cut-off, stage separation and so on. The VEB houses the telemetry instruments that keep a check on more than 1,500 parameters, including the transmitters and antennas that send and receive signals to and from tracking stations on the ground. It is also where the fairing and SYLDA—or SPELTRA on earlier versions—bearing structure are attached.

Upper stage

• For Ariane 5 ECA, the ESC cryogenic upper stage: the HM-7B engine is an upgraded version of the HM-7 engine that has powered the upper stages of every launcher in the series since Ariane 1. It was developed by the Ariane 5 Plus evolution programme for the new ECA variant of the launcher. Like the core stage’s Vulcain 2 engine, it burns liquid hydrogen and oxygen. It operates for up to 15 minutes and 45 seconds, delivering 67 kN (6.7 tonnes) of thrust in vacuum.

• For the generic and ES variants of Ariane 5, the EPS storable propellant stage: the Aestus engine developed for Ariane 5 burned a mixture of liquid mono-methyl-hydrazine and nitrogen peroxide. It was much less powerful than the HM-7B, delivering 29 kN (2.9 tonnes) of thrust in vacuum, but it was reignitable and thus able to inject satellites into different orbits before falling back to Earth.

Payload

Bearing structure: when several satellites are mated atop Ariane 5, they are each held in place until reaching orbit by special bearing structures.

• The first such structure was the SPELTRA (Structure Porteuse Externe pour Lancements Triples Ariane) multiple-launch external bearing structure used for the first three launches of Ariane 5. It was located between the VEB and the fairing and housed a satellite and a short fairing to protect the satellite in the upper berth.

• The bearing structure currently used is a lighter version called SYLDA (SYstème de Lancement Double Ariane) designed for dual launches: one of the satellites is placed on top and the other inside, and both are covered completely down to the VEB by a long fairing. The SYLDA structure spans 4.6 metres and is 4.9 to 7.0 metres tall, depending on the size of the payload. It releases its satellites using pyrotechnic cutters and springs to push them out in a direction perfectly parallel to the trajectory.

• For certain missions, the ASAP structure (Ariane Structure for Auxiliary Payloads) can be used to carry up to eight microsatellites. When launching the European Galileo satellites, Ariane 5 ES used another type of dispenser able to accommodate four satellites.

Fairing: Ariane 5’s fairing is made of two half-shells. Its role is to protect the payloads on ascent through the atmosphere and to make the launcher more aerodynamic. Its short version is 5.4 metres in diameter and 12 metres tall, and its long version 17 metres tall. Its structure is a sandwich composite with an aluminium honeycomb core covered by two carbon skins.
The ACY raising cylinder enables larger payloads (maximum +1.5 metres) to be accommodated.

Three minutes into the flight, at an altitude of about 120 km, the atmosphere is a lot less dense and the fairing can be jettisoned as soon as possible to lighten the upper stage by more than 2 tonnes: the two half-shells are pulled apart by a dual pyrotechnic system and then jettisoned away from the launcher’s trajectory.