Ariane 5's Vulcain engine during XMM campaign

The Vulcain engine represents 30 years of development and constitutes a major programme in itself (a quarter of the total investment). Altogether 40 different European companies, led by France's Snecma Moteurs contributed to the programme. It was in 1957, that the French Ministry of Defence ordered research into cold-temperature propulsion. Associated in a rocket engine, liquid hydrogen and liquid oxygen provide unequalled energetic performance. The problem lay in mastering these two propellants in their extremely cold liquid state. This could only be achieved by using robust architecture and sturdy materials. The first cold-temperature propulsion engine was produced in the United States in 1962, then two years later, the French laboratory that was to give rise to the SEP Company, fired its own version. In 30 years the scale has changed. The 1964 prototype delivered a one-tonne thrust, Ariane-4's third stage can deliver 10 tonnes while the Vulcain engine can deliver 115 tonnes. This progress has been achieved by concentrating an extremely powerful turbopump into a relatively compact volume and by mastering the extreme temperatures entailed.
The Vulcain engine uses liquid oxygen and liquid hydrogen like the Ariane HM7B third stage engine. However, there is an important difference, the Vulcain engine generates three times the pressure and is 20 times more powerful. Although it only provides 8% of the total thrust needed at liftoff it is one of the main technological developments of the new launcher.
Vulcain is 3 m high, 1.76 m in diameter and weighs 1685 kg. It is fixed by gimbals on a thrust frame to the base of the main stage tanks. On either side of its combustion and thrust chamber are two high-speed turbopumps. These force the cryogenic propellants at high pressure into the chamber at a rate of 265 kg/sec.