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Ariane 5 ACS
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Ariane 5 Attitude Control System

A multi-role hydrazine ACS used for launcher ascent control and precision upper stage manoeuvres.

Integration of the 400 N ACS into the Vehicle Equipment Bay. Integration of the 400 N Hydrazine ACS to the Ariane 5 Vehicle Equipment Bay

1. 5.4m diameter Vehicle Equipment Bay.
2. Hydrazine thruster cluster beneath aerothermal cover.
3. Hydrazine bladder tank.
4. 3.936m diameter interface to the upper stage.

Our largest hydrazine thruster is the smallest engine used on the Ariane 5 launch vehicle.


The 400 N hydrazine thruster forms part of the Ariane 5 Attitude Control System (ACS) and is located around the Vehicle Equipment (avionics) Bay (VEB) in 2 modules of three or four thrusters, depending on the mission.


The VEB is located between the main cryogenic stage and the upper stage. It measures 5.4m in diameter, 1.56m high and has a dry mass of up to 1400 kg.


The VEB autonomously manages all systems required for flight control, including engine ignition, booster and upper stage separation.


The functions of the 400 N ACS include roll and pitch control of the launcher after jettisoning of the solid rocket boosters. Thereafter, the same 400 N thrusters are used for fine control manoeuvres and precision upper stage orientation before separation of one or more payloads.


The thrusters are supplied by hydrazine from propellant tanks located within the VEB. Depending on the mission, two to four tanks may be used. Each 58 litre tank contains 39 kg of hydrazine. The hydrazine tanks are pressurised with gaseous nitrogen at lift-off and operate in blow down mode during the mission.


The main elements of the 400 N ACS used on Ariane 5 are:

  • 400 N hydrazine thruster, Model No: CHT 400 (in clusters of three or four thrusters)
  • 58 litre hydrazine tank, Model No: BT/01.


The A5 ACS is available in 4 configurations ( P1, P1+, GS and VUS (also named P2))

Detailed views of the 400 N Hydrazine ACS:


400 N hydrazine thruster.
Enlarge400 N
Hydrazine thruster cluster.
Enlarge3 x 400 N Thruster
Hydrazine thruster cluster.
Enlarge4 x 400 N Thruster
Hydrazine ACS tank in VEB.
EnlargeHydrazine Tank
Integrated to VEB