ESC-A – Cryogenic upper stage

The Ariane 5 ECA launcher version utilizes the ESC-A cryogenic upper stage, which is powered by an HM7B engine.  This reliable engine – which also served in the upper stage on Arianespace’s legendary Ariane 4 family of launchers – develops 67 kN maximum thrust in vacuum, and is turbopump-fed and regeneratively cooled. Its thrust chamber is fed by two pumps (liquid hydrogen and liquid oxygen) driven by a gas generator, a common turbine and a gearbox.

During the powered flight, the attitude control in pitch and yaw is ensured by gimballing of the engine’s nozzle, while gaseous hydrogen thrusters are used for roll control.  In the ballistic phase, roll, pitch and yaw control uses clusters of gaseous hydrogen thrusters, while gaseous oxygen thrusters also are employed for longitudinal boosts.