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Part of HM7
SEP, Ottobrunn LOx/LH2 rocket engine. Increased performance version of the HM-7 engine for the Ariane 2 and 3. Combustion chamber pressure raised from 30 to 35 bar and nozzle extended. First flight 1984.

Number: 142 . Thrust: 70.00 kN (15,736 lbf). Unfuelled mass: 155 kg (341 lb). Specific impulse: 447 s. Specific impulse sea level: 310 s. Burn time: 731 s. Height: 1.80 m (5.90 ft). Diameter: 1.00 m (3.20 ft).

With the introduction of Ariane 2 and Ariane 3, it became necessary to increase the performance of the HM-7 engine. This was achieved by raising the combustion chamber pressure from 30 to 35 bar and extending the nozzle, thereby raising the specific impulse. The burn time was also increased from 570 to 735 seconds. The upgraded engine was designated HM-7B and was qualified in 1983. The HM-7 engine versions have reliably powered the third stages of Ariane's 1 through 4 from 1979 to 2003.

The HM-7B engine, was also integrated from the third stage of Ariane 4 into the new Ariane 5 cryogenic upper stage - a tribute to the performance and flight proven reliability of an engine first developed 30 years earlier. The resulting upper stage was designated ESC-A (Etage Superieur Cryotechnique A) and increased the performance of Ariane 5 to 10 metric tons.

Use of HM-7B on Ariane 5 was a first step toward increasing the launcher's payload performance. A second step was the introduction of the new Vinci expander cycle engine to a new cryogenic upper stage, increasing the payload performance to 12 metric tons.

The Ottobrunn facility was responsible for the development and manufacture of the HM-7B thrust chamber comprising the regeneratively cooled combustion chamber, coaxial propellant mixing injectors, dump cooled nozzle extension, gimbal joint, and the LOX and LH2 propellant valves.

Important principles used in the HM-7 combustion chamber were adopted by NASA under license and it was this technology that formed the basis of the US space shuttle main engines - the first reusable rocket engine in the world.

Thrust (sl): 43.600 kN (9,802 lbf). Thrust (sl): 4,444 kgf. Engine: 155 kg (341 lb). Chamber Pressure: 35.00 bar. Area Ratio: 83.1. Thrust to Weight Ratio: 41.2516129032258. Oxidizer to Fuel Ratio: 5.14. Coefficient of Thrust vacuum: 1.89575424141004.

Country: France. Launch Vehicles: Ariane 2/3, Ariane 4, Ariane 44LP, Ariane 44L, Ariane 42P, Ariane 44P, Ariane 42L. Propellants: Lox/LH2. Stages: Ariane 2-3 H10, Ariane 4-3 H10plus, Ariane 4-3 H10-3, Ariane 5-2 ESC A. Agency: Ottobrunn.

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