Int. J. Impact Engntl Vol. 13, No. 2, pp. 353-365. 1993 0734-743X/93 $6.00 + 0.00 Printed in Great Britain '~', 1993 Pergamon Press Ltd DYNAMIC RESPONSE OF THE SPACE STATION FREEDOM DUE TO A MODULE PERFORATION BY A HYPERVELOCITY IMPACT JOHN P. CELESTIAN a n d WILLIAM P. SCHONBERG Department of Civil and Environmental Engineering, University of Alabama in Huntsville, Huntsville, AL 35899, U.S.A. { Received 5 October 1992; and in revised form 12 November 1992) Summary The perforation of a habitable module that is part ofan extended lifetimespace structure in earth orbit by an orbital debris particle will result in a thrust normal to the module surface. The thrust is caused by air exhausting through the hole in the module wall created by the hypervelocity debris particle impact. This paper addresses the ensuing global dynamic response of the Space Station Freedom following such a module rupture, assuming that structural integrity is maintained. The truss segments of the Space Station Freedom are idealized as finite beam elements; discrete masses modeling various space station elements are lumped at appropriate discrete coordinates. Duhamel's integral is used to solve the governing equations of motion to obtain displacements and accelerations. By varying the size of the hole through which the module air is allowed to escape, an in-depth study of the dynamic response of the Space Station Freedom to a perforating hypervelocity impact is performed. It is shown that significant displacements and accelerations could result from such an impact, especially if the resulting hole diameter is of the order of 15 cm or more. INTRODUCTION One element critical to the survival of an extended lifetime space structure, such as the NASA Space Station Freedom (SSF), is its ability to survive hypervelocity impacts by meteoroids and pieces of orbital debris. Various estimates predict a total of 1.3-3.2 million kg of orbital debris within 2000 km of the earth's surface [ 1-2]. Although the likelihood of a sizable hypervelocity impact (HVI) is marginal, a HVI by a particle greater than 1 cm in diameter on one of the SSF's habitable modules may result in a rupture of a module pressure wall. Large particles of orbital debris (greater than 10 cm in diameter) can be tracked from earth and avoided; however, small (less than 1 cm in diameter) and medium sized debris particles (between 1 and 10 cm in diameter) are a notable threat that cannot be avoided easily. A major effort has been devoted by NASA to protect the SSF against damage from small HVIs (see, e.g. [3-5]). Other research regarding the SSF and the effects of hypervelocity impacts has been primarly devoted to local response, such as pressure wall damage and the damage of external spacecraft systems (see, e.g. [6-9]). These efforts have attempted to correlate the hole size with particle size, shape, density, velocity and impact obliquity [ 10,11 ]. However, little or no work has been performed to examine the effect of a HVI with a module on the dynamics of the SSF. The majority of the work addressing SSF dynamics has been devoted to the dynamics of the truss/module system and to various control schemes [ 12]. The focus of this paper is the ensuing response of the SSF following a perforating HVI on one of its modules. For an overview of the orbital debris environment, a discussion of debris modeling and analysis efforts through 1988, and an overview of design considerations for mitigating the threat of orbital debris impacts, the reader is referred to Ref. [13]. The work presented herein was motivated by the fact that the perforation of a module pressure wall by an orbital debris particle will result in a thrust normal to the module surface due to air exhausting through the hole. This gives rise to several issues, such as whether or not the thrust will cause the modules to break free from the truss, whether or not the SSF will de-orbit, and the nature of the vibrations that would follow a HVI if the 353