The coilgun is an asynchronous linear motor. A conductive projectile is accelerated by a quickly changing magnetic field produced by stationary coils. An optional plasma window separates the vacuum inside the coilgun from the atmosphere. The demand for electric power is much lower than that of the railgun, especially if the coilgun is long. The most serious shortcoming is the high cost of switches controlling the power. The minimum mass is 105 tons.
A superconductive version of the coilgun is called quench gun. Resistors attached to superconductive coils heat them up and thereby change their state to normal (non-superconducting). The quenched coils generate a great amount of heat. A cryogenic refrigerator removing the heat would have to be so large that a quench gun cannot be seriously considered as a means of space transportation.
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