Hypervelocity impact on spacecraft carbon fibre reinforced plastic/aluminium honeycomb

Samples of a spacecraft primary external wall structure, as used in a low earth orbit remote sensing platform, have been tested to determine the response to the hypervelocity impact and ballistic limit (for mm-sized impactors) of the 47 mm thick structure at 5 km/s. A strong dependence of the ballistic limit on projectile density was identified. This programme was carried out using the two-stage light gas gun at the University of Kent at Canterbury. The equivalent diameters of the front and rear holes for each impact were analysed as a function of the impactor parameters. Damage equations derived by other experimenters were compared to the experimental results. X-ray non-destructive testing was used to determine the level of internal honeycomb damage for a sample. The dependence of the witness plate damage (placed behind the target to capture any ejecta from the rear surface) on the impactor parameters was recorded. It was found that the use of 'equivalent thicknesses' of aluminium may not be appropriate as a general conversion factor for carbon fibre reinforced plastic (CFRP) facesheets. A simple damage equation is presented, based on the total hole size as a function of the impact energy. The ballistic limit cannot be defined solely in terms of impact energy and shows an additional dependence with projectile density. The amount and type of ejecta produced is a strong function of density and a less strong function of projectile diameter, and its production cannot be linked with the rear hole diameter.