The Vinci engine uses an expander cycle that avoids the use of gas generators to drive its turbopumps, thereby reducing the risk of explosions and enhancing both reliability and safety, the French space agency said. Vinci's hydrogen turbopump, the size of a small backpack, produces 2.5 Megawatts of power.

CNES said Vinci has now undergone six successful test firings, the last of which was on Feb. 22, and the engine operated for up to 350 seconds. The tests, "during which Vinci was fired at full thrust for the first time, confirmed the high hopes riding on this new-generation rocket engine," the agency said, adding that engineers have scheduled a second round of tests for later this year, after which it will undergo a three-year demonstration phase to confirm its viability.

Vinci delivers about 18 metric tons of thrust and can be restarted several times in succession. Arianespace is eyeing the powerplant as the third stage of its Ariane 5 ESC-B rocket as a way to boost launch capacity. CNES said the engine also could be adapted for lighter vehicles such as Vega, and even the next-generation European launchers.

Using liquid oxygen as an oxidizer and liquid hydrogen as fuel, with a mixture ratio of 5:8, Vinci develops a baseline thrust of about 40,000 pounds, at a combustion-chamber pressure of about pounds per square inch. The engine is capable of burning longer than 464 seconds.

The engine uses an expander type closed operating cycle. The energy required to drive the turbines is provided by heating the hydrogen, which first flows through a regenerative cooling circuit around the combustion chamber and the upper part of the nozzle.

Two valves control propellant supply to the combustion chamber, while two other turbine bypass valves regulate turbopump power, which in turn controls mixture ratio and thrust. The extendible nozzle comprises an upper, regeneratively cooled part and an extension made of composite material.

One feature of the engine is it can be restarted in flight, using an electric igniter.

Vinci was developed by Snecma Moteurs under ESA oversight, assisted by the project team at CNES's Launch Vehicles Directorate.

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