Axis-Symmetric Ram Accelerator Projectile Performance Characteristics

Abstract

The railed-tube ram accelerator is a launch device capable of accelerating a projectile to hypersonic speed. The device has the potential for future space launch and the current application involves oil drilling and tunnel drilling. The railed-tube ram accelerator is a derivative of a smooth-bore ram accelerator in that it uses a railed-tube insert to guide and stabilize the projectiles without the need to utilize finned projectiles. The initial experiments on the prototype railed-tube ram accelerator with axis-symmetric projectiles at entrance velocity of 1030 m/s have demonstrated acceleration up to a velocity of 1120 m/s using a propellant mixture of 1.0 CH4 + 9.52 Air at 16-atm fill pressure. The velocity gain of 90 m/s across the 2-m-long railed-tube ram accelerator corresponds to an average acceleration of 4,900 g. Compared to the theoretical performance model of the thermally-choked ram accelerator, the prototype railed-tube ram accelerator only produces a fraction of the predicted thrust. Gasdynamic starting of the projectile was observed at velocities as low as ~800 m/s, which indicates the potential for ram accelerator starting at low velocities in railed-tubes.