Aestus

Aestus is a hypergolic liquid rocket engine used on an upper stage of Ariane 5 family rockets for the orbital insertion. It features unique design of 132 coaxial injection elements causing swirl mixing of the MMH propellants with nitrogen tetroxide oxidizer. The pressure-fed engine allows for multiple re-ignitions.

== Operations == Fuel and oxidizer are stored in two aluminium alloy tanks, fuel tank is spherical while oxidizer tank is enlarged due to different volumes required from engine operations. Before engine is started it is purged with helium and fuel is pressurized. Then oxidizer valve is opened in a center of injector followed by fuel injectors arranged on a chamber wall. Hypergolic propellants spontaneously ignite on contact expanding to supersonic velocities and escaping through cooled nozzle extension.