1 HYPERVELOCITY IMPACTS ON THIN BRITTLE TARGETS: EXPERIMENTAL DATA AND SPH SIMULATIONS

The meteoroids and debris environment play an important role in the reduction of spacecraft life time. Ejecta or secondary debris, are produced when a debris or a meteoroid impact a spacecraft surface. These ejecta can contribute to a modification of the debris environment: either locally by the occurrence of secondary impacts on the component of complex and large space structures, or at long distance by formation of small orbital debris. This double characteristic underlines the necessity to model the damages caused by an HVI as well as the material ejection caused by the impact. Brittle materials are particularly sensitive to hypervelocity impacts because they produce features larger than those observed on ductile targets and the ejected fragments total mass including ejectas and spalls is in the order of 100 times bigger than the impacting mass. The French atomic energy commission (CEA) faces to the same problem in the Laser MégaJoule project (LMJ). The various instruments used in the experiment chamber will undergo many aggressions resulting from target disassembly. Thus the lasers optics will be bombarded as hypervelocity debris and shrapnel. In this study, the authors only focus on potential impacts of debris and shrapnel on fused silica optical debris shields. These Main Debris Shields called MDS are 20mm thick fused silica plates placed in front of each lasers way out. 2 mm thick Disposable Debris Shields, DDS, located in front of the MDS might be used to stop vapour, particulate, droplets and substantially reduce very small shrapnel cratering on the main debris shields. But ejecta from the rear surface of th