To obtain solid density projectiles traveling at ultra-hypervelocity ( > 100 km/s) several issues must be addressed. For any accelerator, limitations on the strength of materials (either projectile or accelerator structure) indicates that the accelerator length needed to achieve a desired projectile speed is measured in units of the projectile length. This suggests that almost arbitrarily high speeds with stable flight could be attained in reasonable accelerator lengths simply by reducing projectile dimensions. Acceleration techniques involving chemical energy cannot achieve ultrahypervelocity (without severe inefficiency). Electromagnetic methods, such as railguns, involve conductor heating and possibly friction, so that very small projectiles will overheat before reaching ultrahypervelocity. Non-diffusive techniques for acceleration are thus required. At present, only electrostatic forces offer the opportunity to accelerate at the limits of high strength material while avoiding undue heating. An electrostatic accelerator technique for microprojectiles is being developed based on a multistage system using the sequential application of moderate-voltage pulses (greater-than-or-equal-to 100 kV). Preliminary experiments have shown that carbon fibers have adequate tensile strength and conductivity to achieve charge-to-mass ratios greater-than-or-equal-to 1 C/kg, a value consistent with hypervelocity goals. The carbon microprojectiles have been used in a five-stage proof-of-principle prototype accelerator at stage voltages of 35 kV to attain velocities of 0.5 km/s. Through the use of schlieren imaging techniques, data has been obtained showing that good control of the projetile trajectory can be achieved with electrostatic aperture focusing methods. Information from these experiments is being used to design and construct a 10 - 20 km/s prototype accelerator. To obtain a relatively short accelerator, encapsulation techniques are being developed so that acceleration gradients approaching the high dielectric strengths of the encapsulants can be achieved. A new reflex transmission line arrangement has been devised that permits the longitudinal accelerating field to follow the projectile motion along the multiple stages with minimal switch action and without reversing electric field vectors that would degrade dielectric strength. This paper will present details on the accelerator concept, the experimental results, and hardware designs.
