Ram-accelerator: A new hypervelocity launcher for ballistic studies

Summary Investigations are conducted at ISL on new hypervelocity launchers to fulfill requirements in different fields of ballistics such as launching dynamics, aeroballistics, terminal ballistics, aerothermodynamics, and supersonic combustion studies. One objective considered is to determine the operational conditions to accelerate a 90mm-caliber projectile with a mass of ~1.5kg to a velocity of 3km/s while keeping the acceleration level below 40,000g. This moderate level of acceleration is required to investigate at high velocities models that are fragile because of their design and/or their onboard opto-electronical equipments. A means to fulfill these velocity and acceleration requirements is ram-accelerator technology. This paper presents research conducted at ISL with smooth-bore ram-accelerators in the thermally choked propulsion mode. Therefore, two accelerators in calibers 30 and 90mm respectively, operated within the launch room of the aeroballistic range facility are described. Experimental results are presented describing the two-fold strategy followed to achieve the maximum performance, i.e., optimization of the projectile configuration and optimization of the combustible gas mixtures. To date a maximum velocity of about 1985m/s has been achieved with the 90mm accelerator (projectile mass = 1.34kg, ram-section length 16.2m, injection velocity in the ram-section 1330m/s) and 2380m/s with the 30mm accelerator (projectile mass 68.6g, ram-section length 9m, injection velocity in the ram-section = 1380m/s). Potential applications of ram-accelerators for ballistic studies are discussed and performances compared to those of conventional launchers that are currently used at ISL for ballistic studies. Finally, very first preliminary experiments are presented describing the acceleration of high l/d rods using a ram-accelerator.