Columbus debris shielding experiments and ballistic limit curves

An extensive Light Gas Gun test campaign has been performed to develop a high resistance shielding to protect the Columbus module - the European laboratory attached to the International Space Station - against the threat posed by orbital debris. In a 3-year period from Summer '95 to Summer '98 - more than 100 hypervelocity impact tests have been made on a 3-wall shield system, based on an aluminium Whipple Shield plus an intermediate bumper made of Nextel fabric and a Kevlar(TM)-Epoxy(TM) plate. Two shielding configurations have been selected, which both reported excellent ballistic performance against aluminium spherical projectiles impacting with velocities between 3 and 7 km/s and angles between 0 and 60 degrees. The results showed that the response of a 3-wall system to hypervelocity impacts is more complex than expected. For instance - in the test range - the shielding resistance does not increase linearly with the velocity but shows non-monotonic variations; the ballistic limit shows little oscillations with the increase of the impact angle in the 0 - 45 degrees range as well. The projectile fragmentation level is shown to play a key role in the target failure process. A thorough analysis of the impacted target is on going to gain insight into the complex damage mechanism with particular attention paid to the X-ray pictures taken of the debris cloud formation and evolution. The present paper summarizes the activities performed and the results obtained so far, focusing on the more recently performed experiments. (C) 1999 Elsevier Science Ltd. All rights reserved.