Characteristic analysis of acoustic emission signals caused by debris cloud impact

In order to understand the characteristics of acoustic emission signals caused by hypervelocity space debris impacting spacecraft with shields, a two-stage light gas gun was used to launch sphere projectiles to impact an aluminum-alloy Whipple shield, the induced acoustic emission signals were acquired, and analyzed by wavelet packet technology and energy entropy theory. The experimental results indicate that, the initial velocity of projectile, bumper thickness and projectile diameter are important factors to decide the form of debris cloud and characteristics of acoustic emission signals. The wavelet packet energy entropy could be used to describe the frequency complexity of debris cloud impact signals. When the initial velocity of projectile increases in the broken section (3-7 km/s), along with which the projectile breaks more completely and the energy entropy of acoustic emission signals increases. Under the experimental conditions, the bumper thickness has greater influence on energy entropy values than the projectile diameter. The wavelet packet energy entropy is helpful to estimate the initial velocity of projectile and the maximum impact damage region, combined with the predicted curve from the Christiansen ballistic limit equation, the damage pattern recognition of the bulkhead could be assessed.