Development of a plasma railgun for affordable and rapid access to space

The Institute for Advanced Technology (IAT) of The University of Texas at Austin (UT) is developing a plasma-driven railgun to launch low-mass projectiles of roughly 5–10 g to a velocity in excess of 7 km/s. Accomplishing this goal requires overcoming the problem of bore ablation, which has been linked to an observed velocity ceiling of about 6 km/s in plasma armature launchers. Bore ablation is a direct consequence of the intense heat radiated by plasma armatures. Controlling bore ablation requires a coordinated approach that includes: 1. using magnetic augmentation to reduce power dissipation in the plasma, 2. using high-purity alumina insulators to raise the ablation resistance of the bore, 3. using pre-acceleration to prevent ablation of the bore materials at low velocity, and 4. using a synchronously driven, distributed power supply to electrically isolate stages.

I. Introduction

Research efforts are currently under way at the IAT to develop electromagnetic launch technology that might someday be used to launch microsatellites into low-earth orbit. The effort is part of a multidisciplinary university research initiative (MURI) sponsored by the Air Force Office of Scientific Research (AFOSR). Electromagnetic (EM) launch to space has been an appealing concept since the first demonstration of hypervelocity launch in the late 1970s [1]. In order to accomplish this goal, a railgun must accelerate the payload to roughly 7 km/s. Because solid armatures have a velocity ceiling of around 3 km/s, plasma armatures must be used. However, several decades of railgun research showed a persistent velocity ceiling of about 5–6 km/s for plasma-armature launchers. Railgun researchers working in the early 1970s had assumed that plasma armature railguns should be able to achieve exit velocities of tens of kilometers per second; however, they were only able to achieve velocities of 4–5 km/s for medium-bore (25–50 mm) railguns operating at typical accelerations of 400–600 kG [2], [3], and 6–7 km/s in smaller-bore guns operating at 1 MG or greater [4], [5]. These fast accelerations enabled researchers to outrun most of the problems that contribute to the velocity ceiling. Many of the reasons for the velocity ceilings in each of these cases were discovered in the 1980s [6], [7], and several suggestions were made to eliminate them in the early 1990s. However, just as positive results were starting to be observed, funding shifted and the programs were discontinued.