Int. J. Impact Engng Vohl4, pp.647-658, 1993 0734-743X/93 $6.00+0.00 Printed in Great Britain © 1993 Pergamon Press Ltd RESPONSE OF SPACE STRUCTURES TO ORBITAL DEBRIS PARTICLE IMPACT William P. Schonberg and Fengwei Yang Mechanical Engineering Department University of Alabama in Huntsville Huntsville, AL 35899 ABSTRACT All long-duration space and aerospace support and transportation systems, such as the Space Station Freedom and the Space Shuttle, are susceptible to impacts by pieces of orbital debris. These impacts occur at high speeds and can damage the flight-critical systems of such spacecraft. Therefore, the design of a structure that will be exposed to a hazardous orbital debris environment must address the possibility of such hypervelocity impacts and their effect on the integrity of the entire structural system. A technique is developed for analyzing the response of dual-wall structures to oblique hypervelocity projectile impact. Ballistic limit curves that predict the potential of an impacting projectile to perforate the main wall of a dual-wall structural system are obtained using the technique and are compared against experimentally derived curves. Comparisons are performed for a variety of impact velocities, trajectory obliquities and projectile masses. It is shown that the results obtained using the technique developed herein compare very well with experimental results. INTRODUCTION All earth-orbiting spacecraft, especially those with a mission duration of more than a few days, are susceptible to high-speed impacts by pieces of orbiting debris. These orbital debris particles range in size from microscopic solid propellant particles to spent rocket boosters still in low earth orbit. The impacts of these particles, which can occur at speeds as high as 12 to 14 km/sec (Kessler, 1982), can damage flight-critical systems and lead to catastrophic failure of the spacecraft (Kessler and Cour-Palais, 1978; Kessler, 1981; Reynolds et al, 1983). Therefore, the design of a long duration spacecraft in earth orbit must take into account the effects of such impacts and must contain protective systems to insure its integrity and the safety of its occupants. The design of protective systems for earth-orbiting structures largely depends on the ability to predict the response of a variety of structural components to hypervelocity impact. Forty- five years ago it was suggested that a 'bumper' could be used to minimize the damage caused by meteoroid impact (Whipple, 1947). Since then, numerous investigations have been performed to study the effectiveness of multi-sheet structures in reducing the damage threat of hypervelocity projectiles (Wallace eC ai, 1962; Maiden and McMillan, 1964; Lundeberg et ai, 1966; Wilkinson, 1969; Swift et al, 1983). Dual-wall configurations were repeatedly shown to provide significant increases in protection against perforation by hypervelocity projectiles over equivalent single- wall structures. Recent experimental investigations of oblique hypervelocity impact phenomena have shown that the response of a dual-wall structure to oblique hypervelocity projectile impact is significantly different from its response to normal hypervelocity impact (Coronado et al, 1987; SchonberK and Taylor, 1989). Unlike normal high-speed impacts, oblique impacts can produce a tremendous volume of ricochet debris particles which can severely damage panels of instrumentation units located on the exterior of a structure (Schonberg, 1989). Obliquity effects, therefore, must be considered in the design of a space structure that will be exposed to the orbital debris environment. A wide variety of analytical models exist that predict the response of thin plates to normal impact loadings. On the other hand, only a relatively small number of models have been developed for oblique impact. Many early analytical perforation studies were performed in an attempt to model the response of armor to impacts by bullets and bullet-like projectiles at impact speeds less than 2 km/sec (see e.g., Taylor; 1948, Thomson; 1955, Zaid and Paul, 1957; Paul and Zaid, 1958). Although the importance of trajectory obliquity was occasionally studied (Zaid and Paul, 1959; Recht and Ipson, 1963), the problem of normal impact was usually solved because the assumption of axisymmetric response made it much more tractable mathematically. More recent attempts at modelling thin plate perforation by normally impacting projectiles have included elastic/plastic and visco-plastic analyses (Goldsmith et al, 1965; Calder and Goldsmith, 1971; Levy and Goldsmith, 1984) and comprehensive mechanics-of- materials approaches (Ravid and Bodner, 1983; Awerbuch, 1970; Awerbuch and Bodner, 1974). 647