Artist's drawing of Pulse Detonation Propulsion System. Photo: NASA

Technology for a rocket engine that uses an automotive ignition system to initiate supersonic combustion waves is being tested at NASA's Marshall Space Flight Center in Huntsville, Ala.

Component testing of a small-scale pulse detonation rocket engine began in April. A spark plug is discharged to ignite hydrogen fuel in a small initiator tube, about 4 inches long and one-half inch in diameter. The hot firings, which last 5 to 10 seconds, demonstrate pulse detonation principles and help researchers evaluate engine performance.

Following last month's successful testing of the initiator tube, engineers finalized their design and started building a primary tube - about 3 feet long and 2 inches in diameter - which will be connected to the initiator tube.

Using only a small amount of spark energy, a detonation wave can be created in the initiator tube and propagated into the larger primary tube where the main propellants are burned at an extremely high rate.

Like automobile engines, pulse detonation rocket engines operate by injecting fuel and oxidizer into long cylinders and igniting the mixture with a spark plug. The explosive pressure of the detonation pushes the exhaust out the open end of the cylinder, providing thrust to the vehicle. Pulse detonation rocket engine technology development could lead to lightweight, low-cost space transportation systems.