Influence of Projectile Geometry on Baffled Tube Ram Accelerators

Abstract

The ram accelerator is a hypervelocity mass driver that operates on a principle similar to that of a ramjet in tube. It is capable of accelerating projectiles to velocities in excess of 2.6 km/s and has applications in direct space launch, impact assisted drilling, and defense. The baffled tube ram accelerator is a derivative of the ram accelerator that was invented in order to enlarge the operational envelope by enabling a lower start velocity and allowing for the use of propellant mixtures with higher heat release. The influence of projectile geometry on baffled tube ram accelerators was experimentally investigated in an effort to identify the optimum projectile geometry. Geometric variations included the nosecone angle, tailcone angle, projectile shoulder diameter, and projectile shoulder length. Performance was evaluated based on total delta-v, thrust produced, and projectile stability. Results indicate that nosecone performance has a Mach number dependence. Short nose projectiles produced higher relative thrust at low Mach numbers while long nose projectiles had higher relative thrust at high Mach numbers. Thrust was found to increase with increasing tailcone length. Thrust is maximized at approximately 92% projectile shoulder-to-baffle bore ratio and was shown to increase with increasing shoulder length.