Basic principles of coaxial launch technology

Coaxial launchers have received very much less attention than railguns because of their greater complexity, but they offer several significant advantages. They require no physical contact with the projectile, scale readily to very large diameter, can distribute thrust over the length of the projectile, have more adaptable energy supply and impedance requirements (being a multi-turn device), offer higher efficiency, positive control over the launch cycle, and permit component redundancy to achieve any desired degree of reliability. Thrust for a given current can be a hundred times higher than in a railgun, but the current must be synchronized with projectile motion. The voltage required to do so increases with velocity, and high voltage commutation capability represents the technological limit to launch velocity. Present research activity is concerned with commutation in the low and high velocity domains, position sensing techniques, dynamic stress containment in drive coils, and design of the first practical EM launcher: a Nimitz class aircraft catapult.