Rail Gun: How it Works
A Rail Gun is a device that uses electromagnetic forces to accelerate projectiles to high velocities. A strong pulse of electricity is sent through a pair of parallel rails, generating a magnetic field that accelerates a conducting projectile to speeds sufficient to send it high into the atmosphere. With only a little further rocket assistance, small payloads may eventually be orbited in this way at relatively low costs.
As with many technological concepts, the notion of using a large gun to fire an object directly into orbit dates back to Jules Verne. By the late 19th century this notion had already been considered in the electromagnetic format that the railgun was to assume, but no large-scale project devoted to the concept got under way until the 1970s. In the 1980s the railgun became part of the U. S. Strategic Defense Initiative (SDI).
Although the SDI program declined, researchers continue to work on electromagnetic launchers. In the simplest railgun design, an electric current passes up one of two parallel rails, through a metal armature (a cylinder around the projectile), and down the other rail. The magnetic field thus generated sends the armature down the gun while in contact with the rails. As the projectile exits, the armature falls to the ground. One problem with the railgun is that the contact between rails and projectile heats the air so much that a plasma is produced, softening the rails. A more complex version called a coilgun uses a series of metal coils to which electric current is applied sequentially, producing magnetic pulses along the entire length of the gun. In addition, the projectile is suspended magnetically and does not touch the coils. These and other launcher designs remain in the development stage.
Bibliography: Scott, D., “Workin’ on the Railgun,” Ad Astra, June 1990.