Performance of whipple shields at impact velocities above 9 km/s

摘要

Whipple shields were first proposed as a means of protecting spacecraft from the impact of micrometeoroids in 1947 [1] and are currently in use as micrometeoroid and orbital debris shields on modern spacecraft. In the intervening years, the function of the thin bumper used to shatter or melt the threatening particles has been augmented and enhanced by the use of different types and configurations of intermediate layers of various materials. All shield designs serve to minimize the threat of a spall failure or perforation of the main wall of the spacecraft as a result of the impact of the particles. Various ballistic limit or "failure" equations for guiding the design and estimating the performance of Whipple shield systems have been developed. Most of these equations were developed in the 1960's and were used to estimate the performance of shields designed to provide protection against the extremely high impact velocities of micrometeoroids (11 km/s to 72 km/s). With the subsequent emergence of orbital debris as a more serious threat to spacecraft shielding, additional relationships were required for predicting the performance of shields impacted by lower velocity particles. Hayashida and Robinson [2] examined seven commonly used double-plate penetration equations for their accuracy and effectiveness in the development of shield designs. The best known and most used of the equations was the set of "new" modified Cour-Palais or Christiansen equations [3]. These equations were the only equations which addressed the three phases of impact: (1) ballistic (<3 km/s), where the projectile essentially penetrates as an intact projectile; (2) shatter (3 to 7 km/s), where the projectile fragments at impact and forms an expanding cloud of debris fragments; and (3) melt/vaporization (>7 km/s), where the projectile melts or vaporizes at impact. The results of 18 hypervelocity impact tests are presented in this paper. Thirteen test firings were made using three scales of a simple Whipple shield as targets and five test firings were made using a one-third-scale version of an all-aluminum Whipple shield installed on the U.S. Laboratory Module of Space Station as targets. The result of each test firing was compared to the appropriate ballistic limit curve generated for each of the shield designs. Six test firings, with impact velocities ranging from 6.94 to 7.28 km/s, were made using a two-stage, light-gas gun and twelve test firings, with impact velocities ranging from 8.75 to 9.89 km/s, were made using a three-stage, light-gas gun recently developed at the University of Dayton Research Institute (UDRI) [4].