Ariane 5’s cryogenic main stage is referred to as the EPC from its title in French, Etage Principal Cryotechnique. The EPC is 30.5 m high with a diameter of 5.4 m. When empty it weighs only 12.5 tonnes and approximately 170 tonnes when full of propellant.
The EPC is essentially composed of an aluminium tank with two compartments: one for liquid oxygen and one for liquid hydrogen. The upper compartment contains 133 tonnes of liquid oxygen and has a capacity of 120 m3, while the lower compartment contains 26 tonnes of liquid hydrogen and has a capacity of 390 m3. Both propellants are produced at plants located inside Europe’s Spaceport in French Guiana.
The tanks are only a few millimetres thick: 1.3 mm for the hydrogen and 4.7 mm for the oxygen. Given the structural characteristics of the main stage, when the tanks are empty they have to be pressurised to prevent them buckling under their own weight. Innovative technology and extremely precise welding machines are needed to produce them.
At the base of the EPC is the Vulcain engine which transmits thrust to the launcher through the aft ‘skirt’, while at its summit is a forward ‘skirt’ linking the main stage to the launcher’s upper stage and upper part configuration. This element, called JAVE from its name in French "Jupe AVant Equipée", is a major structure of the launcher as it transmits thrust from the two solid boosters to the launcher in order to lift the fully loaded EPC.
The Vulcain engine operates for just under 10 minutes before it shutdowns. At this point, at an attitude of around 145 km, the main stage separates and follows a side ballistic trajectory during which it is spun on a transversal axis before re-entering the atmosphere. Most of it burns up into the atmosphere and the remaining parts fall into the Pacific Ocean, some 2000 km off the coast of South America.
Responsible contractor: EADS SPACE Transportation (France)
Cryogenic tanks: CRYOSPACE (France)
Thrust frame: Dutch Space(the Netherlands)
Forward skirt: MAN (Germany)
Vulcain engine: SNECMA MOTEURS (France)