Basic principles of coaxial launch technology

Already in the 1930s, a discrete-coil mechanically synchronized launcher was built. At the present time, research is almost entirely directed towards railguns. However, although coaxial accelerators are more complex than railguns, they have certain unique advantages. Some of these advantages are related to the absence of physical contact requirements with the projectile, the possibility of a scale-up to very large projectile size, and the availability of up to 100 times more thrust for a given current. The price of the advantages is the need for a drive current in the form of pulses synchronized precisely with transit of each projectile coil through each drive coil. At high velocities, high voltages are required, and high voltage switching represents the technology limit on launch velocity. Attention is given to inductance gradients, the double hump, methods of excitation, methods of synchronization, projectile configuration, energy supply, fundamental limits, trends, and research needs.