Home of space-propulsion.com

Rocket Engines

Rocket Engines
Vulcain 2
RS 72
300 N

Aestus Rocket Engine

Bipropellant upper stage engine for the orbital insertion of heavy payloads.

Aestus bipropellant rocket engine
Aestus Rocket Engine

The Aestus rocket engine powers the Ariane 5 bipropellant upper stage for the insertion of payloads into LEO, SSO and GTO. Using its re-ignition capability, Aestus is also used on the ES - ATV version of Ariane 5 for the placement of ESA's 21 tonne Automated Transfer Vehicle (ATV) into a low Earth orbit.


Aestus is a pressure fed engine that consumes up to 10 tonnes of the bipropellant combination MMH/N2O4.


Aestus was developed at the Ottobrunn Space Propulsion Centre and has been in operation since 1997.


Major Sub-Assemblies

The Aestus rocket engine comprises the following main sub-assemblies:


  • Gimbal joint mounted at the top of the injector dome.
  • Coaxial injectors for the mixing of propellants.
  • Regeneratively cooled combustion chamber.
  • Nozzle extension, radiatively cooled.
  • Propellant valves for fuel and oxidiser.


The Aestus thrust chamber design is based on the regenerative cooling principle. Prior to combustion, MMH fuel is pressurised into a distribution manifold causing the fuel to flow through narrow, closely arranged channels in the combustion chamber wall, configured to cause a highly efficient cooling.


Before entering the combustion chamber, the propellants are thoroughly mixed within injector elements. MMH enters about the outer wall of the injector element through radially shaped slots. Simultaneously, N2O4 enters axially through the centre of the injector.


The unique design of the injector element causes mixing and atomisation of the propellants enabling combustion efficiencies in excess of 98% to be realised during the remaining process in the combustion chamber.


Ariane 5 bipropellant upper stage with Aestus engine
Enlarge image Ariane 5 bipropellant upper stage with Aestus engine. The upper stage is integrated at Airbus DS Bremen from where it is shipped to Kourou for integration to the launcher.

Upon leaving the injector elements and entering the combustion chamber, the hypergolic propellants spontaneously ignite and are burned and accelerated up to sonic conditions. The combustion temperature in the combustion chamber reaches about 3000 K at a combustion pressure of 11 bar.


Controlling the MMH fuel temperature (20°C to 125°C) against the thin hot wall of the combustion chamber was one of the most challenging tasks that had to be overcome during the development phase.


A further challenging task was the development of a new injector element for MMH /N2O4, using the same, highly efficient, coaxial injection principle used on all of our cryogenic thrust chambers.


After leaving the combustion chamber, hot gases are accelerated to supersonic velocities due to gas expansion in the radiatively cooled nozzle extension, thereby increasing thrust.



Detailed description of the Aestus rocket engine

Proven Design and Performance Flexibility

The Aestus rocket engine has proven to be a robust and flexible design, evolving harmoniously with the evolution of Ariane 5 and its various missions.


In addition, by varying the number of coaxial injector elements, the basic Aestus design can be used for higher, or lower thrust applications.


A turbopump version of Aestus, Known as the RS 72 has also been developed and hot-fire tested in collaboration with Pratt and Whitney Rocketdyne. More information on this Aestus II version can be found on the RS72 rocket engine page.



Aestus Rocket Engine Characteristics
Propellants MON / MMH
Thrust vac 30 kN
Power 43,700 kW
59,400 hp
Specific Impulse vac. 324 sec
Propellant mass flow rate 9.3 kg/s
Propellant mixture ratio 1.9
Engine feed pressure 17.7 bar
Chamber pressure 11 bar
Nozzle area ratio 84
Nozzle diameter 1,315 mm
Overall engine length 2.2 m
Mass 111 kg
Nominal single firing 1,100 sec
Re-ignition capability Multiple



Aestus Brochure (PDF)

PDF Brochure - Aestus bipropellant upper stage rocket engine.


To view and download the brochure, click on the image right.


Click on the button below to download the latest version of the free Adobe Reader.


Get Adobe reader


If you require more detailed information about this product please Contact Us.


See the complete list of space propulsion product brochures available for download.