The authors summarize the problems encountered in attempts to achieve hypervelocities with a railgun. Included is a description of the phenomenology and details of joint Sandia National Laboratories, Albuquerque/Lawrence Livermore National Laboratory (SNLA/LNLL) work at SNLA on a method for forming the needed plasma armature. Attention is given to such problem areas as secondary arc formation through growth and separation of the propulsive plasma armature and arc restrike. Potential solutions to the problems are being incorporated in the STARFIRE railgun project. The primary improvement is to provide a high-injection velocity with a 2SLGG (two-stage light gas gun), which offers the additional benefit of filling the barrel behind the projectile with electrically insulating hydrogen. The resulting additional challenge of forming a propulsive armature behind the projectile has been met with an injected metal vapor and a projectile-mounted fuse which are used to initiate rail commutation and begin the formation of a hydrogen plasma armature.
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