Ram accelerator - A new chemical method for accelerating projectilesto ultrahigh velocities

Abstract

A new method for accelerating projectiles from velocities of ~0.7 km/s up to -12 km/s using chemical energy is presented in this paper. The concept, called the accelerator, is based on gasdynamic principles similar to those of an airbreathing ramjet but operates in a different manner. The projectile, which resembles the center body of a ramjet, travels through a tube filled with a premixed gaseous fuel and oxidizer mixture. The tube becomes the outer cowling of the ramjet, and the energy release process travels with the projectile. By tailoring the propellant mixture along the tube, a nearly constant acceleration can be achieved. In principle, the ram accelerator can be scaled for projectile masses ranging from grams to hundreds of kilograms and is capable of ballistic efficiencies as high as 30%. A straightforwar d, quasisteady, one-dimensional approach is used to model the acceleration process. The experimental facility developed to investigate the concept is described, and the results of recent experiments are presented. The velocity range of 690-1500 m/s has been explored in a 4.88-m long, 38-mm bore accelerator tube. Using methane, oxygen, and various diluents, accelerations of up to 16,000 g have been achieved with 75 gm projectiles and gas fill pressures of 20 atm. Proof of concept has been demonstrated, and agreement between theory and experiment has been found to be very good.