Ram Accelerator

AbstractThe ram accelerator is a scalable hypervelocity launcher capable, in principle, of accelerating projectiles to velocities greater than 8 km s−11. The device operates as an in‐bore ramjet in which a subcaliber projectile, shaped like the centerbody of a cylindrical supersonic ramjet, is propelled through a stationary tube filled with a pressurized gaseous propellant mixture of fuel, oxidizer, and diluent. This propellant burns near the base of the moving projectile, generating thrust. The chemical energy density and speed of sound of the propellant can be adjusted, via gas pressure and composition, to control the in‐tube Mach number and acceleration history. Successful ram accelerator operation has been obtained at gas fill pressures up to 200 bar and projectile velocities up to 2.7 km s−1. Scaling has been demonstrated in bore sizes ranging from 25 to 120 mm in research facilities around the world. Potential applications of the ram accelerator include hypervelocity impact studies, hypersonic propulsion research, and direct launch of acceleration‐insensitive payloads to low Earth orbit. An overview of ram accelerator technology and representative experimental results from a 38 mm‐bore ram accelerator facility are presented.