The Vulcain is considered one of Europe’s great technological successes. It alone cost a quarter of all the investment in the launcher programme, while 40 different European industries contributed to its construction. After ten minutes of uninterrupted thrust, the Vulcain shuts down, the first stage separates from the second stage and returns to Earth following a ballistic trajectory. Most of the first stage burns up in the atmosphere through friction, while what remains falls more than 2,000 km off the coast, in the middle of the Pacific Ocean. During the first few minutes of the launch, the cryogenic engine provides just 8% of the necessary thrust. Most of the work is done by two lateral rocket boosters, the so-called boosters (EAP, Etage d’Accelerationà Poudre), which, at 30 metres high and 3 metres in diameter, devour 240 tonnes of propellant each in just over two minutes. After about 130 seconds from launch, at an altitude of about 55 kilometres, the two boosters are released from the main stage in controlled explosions and plunge into the Atlantic Ocean about 450 kilometres off Kourou. The boosters are also responsible for the changes in the launcher’s direction of travel, because the nozzle at the base of the engine is movable, being able to tilt about 6.5 degrees around the vertical. Unlike the main stage, the rocket boosters are fuelled by solid propellant, a compound consisting of ammonia perchlorate (68%), which acts as an oxidant, aluminium powder (18%), which acts as a reductant, and, finally, polybutadiene (14%), which acts as a binder and catalyst.