The HM7 engine, built upon the development work of HM4, first flew in 1979, powering the third stage of the Ariane 1. The evolved HM7B, with higher specific impulse, powered the third stages of Ariane 2, 3 and 4. It was first used in the Ariane 5 in 2002, when the first ECA version of the launcher flew, although the launch failed before first stage separation, so the first time an HM7B actually powered the upper stage of an Ariane 5 was in 2005. The switch to a cryogenic engine is responsible for more than half of the overall payload increase of the Ariane 5 ECA versus its previous version, the Ariane 5G. The HM 7, HM7B Engine family has 5 failures during its use in Ariane 1 - 4 rockets. Flight V 70 was the last failure of an HM7B.
The HM7B is a gas generator rocket engine fed with liquid oxygen and liquid hydrogen. It has no restart capability: the engine is continuously fired for 950 seconds in its Ariane 5 version (780 s in the Ariane 4). It provides 62.7 kN of thrust with a specific impulse of 444.2 s. The engine's chamber pressure is 3.5 MPa.