<title>Empirical prediction models for hole and crack size in space station shielding from 6 to 12 km/sec</title>

Abstract

Long duration spacecraft in low earth orbit, such as the International Space Station Alpha (ISSA), are highly susceptible to hypervelocity impacts by pieces of debris from past earth-orbiting missions. With this increased likelihood of debris impact over time comes a responsibility on the part of a spacecraft design engineer to quantify, and subsequently reduce, the hazardous effects on the spacecraft and its crew should a penetration occur. Among the various hazards that accompany the penetration of a pressurized manned spacecraft module are critical crack propagation in the module wall (i.e. the so-called 'unzipping' of the module) and depressurization-related phenomena, such as crew hypoxia and uncontrolled thrust due to air rushing out of the module wall hole. These phenomena are directly related to the hole size and crack lengths that result in a spacecraft wall following a penetration. As a result, accurate models for hole size and crack size resulting in thin-walled spacecraft structures following hypervelocity impact penetration are required for accurate spacecraft quantitative risk assessments. This paper presents the results of a study whose objectives were to develop semi- empirical models of hole size and tip-to-tip crack length for some of the multi-wall shielding systems being developed for ISSA. The empirical models were developed using light gas gun test data at impact velocities around 6.5 km/sec, and inhibited shaped charge test data at an impact velocity of 11.3 km/sec. The significance of the work performed is that these models can be incorporated directly into a survivability analysis to determine whether or not module unzipping would occur under a specific set of impact conditions. In addition, the prediction of hole size can be used as part of a survivability analysis to determine the time available for module evacuation prior to the onset of incapacitation due to air loss.