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In 1973, the Ottobrunn team started development of the HM-7 thrust chamber for Ariane's upper stage rocket engine. Six years later, the HM-7 engine was successfully qualified with the first launch of Ariane 1 in December 1979. The HM-7 rocket engine featured Ottobrunn's unique regenerative cooling technology whereby hydrogen propellant was efficiently used to cool the combustion chamber before being injected for combustion.