Zero-ablation tests on the HART augmented launcher

The authors describe the results of tests conducted below and above the ablation threshold of Al₂O₃ insulators on the HART augmented launcher. In these tests projectiles were accelerated to 4 km/s without incurring thermal ablation of the bore materials. Comparison of shots below and above the ablation threshold showed a marked difference in armature structure and behavior. Nonablating armatures showed no signs of conventional secondary or restrike arcs. Furthermore, a double peaked structure that formed early in many of the nonablating shots showed a tendency to merge or heal, suggesting an inherent stability in the armature. The measurements show that augmentation provides the expected increase in force without increasing the power dissipation in the armature. The test results are consistent with the reported theoretical value of 12 MWs^1/2/m ² for the ablation threshold of Al₂O₃