Washington Research Foundation

Keith A McFall

Abraham Hertzberg

Adam P Bruckner

Carl Knowlen

A method and apparatus for initiating a ram acceleration of a projectile that is at rest. A projectile (34) is positioned in a starting chamber (14) of a launch tube (12). Starting chamber (14) is either filled with a gas at a relatively low pressure or is substantially evacuated. A wave reflection disk (42/42') is positioned a short distance behind the projectile. Downstream of the starting chamber are a plurality of segments, including a first segment (16), which is filled with a combustible gas mixture at a substantially higher pressure than that in the starting chamber. The first segment is separated from the starting chamber by a pair of thin membranes (20a and 20b). These membranes have a characteristic burst pressure that is about midway between the differential pressure in the first segment and the starting chamber. To initiate the ram acceleration process, fluid between the two membranes is exhausted to the atmosphere, sequentially exposing them to a differential pressure that exceeds their burst pressure. Bursting of these membranes enables the combustible gas mixture to expand unsteadily from the first segment into the starting chamber. An expansion wave produced by the expanding combustible gas mixture passes the projectile and reflects from the wave reflection disk as a shock wave. The wave reflection disk converts the kinetic energy of the expanding gas into thermal energy, at a temperature sufficient to initiate combustion of the mixture. The shock wave propagates downstream from the wave reflection disk, attaches to the projectile, and establishes a stable, thermally choked ram acceleration of the projectile down the launch tube. As the combustible gas mixture burns behind the projectile, the resulting pressure wave accelerates the projectile down the bore of the tube into successive combustible gas-filled segments.

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Keith A McFall