SEM studies of fracture phenomena and wall structure in micrometeoroid impact craters in spacecraft metals

There has been a considerable effort over nearly a decade to examine the size frequencies, compositions, and origins of particles producing impact craters in a variety of materials surfaces on the Solar Maximum Mission spacecraft, retrieved communications satellites (such as Palapa-B2), and more recently the LDEF (Long Duration Exposure Facility) spacecraft. Three regimes of particles have emerged: natural cosmic dust or interplanetary dust particles (IDP's), man-made orbital debris (including paint or other spacecraft component or coating chips having compositions different from the impacted materials); and orbital debris, often spacecraft debris or secondary (ejecta) debris, having the same composition as the impacted material. However more than 50% of all LDEF impacts into metallic targets did not yield sufficient projectile residue to permit analysis using EDS techniques in electron beam instruments (SEM or STEM in particular).There have been very few attempts to investigate the microstructural and microchemical nature of the micrometeoroid crater walls, especially in the context of the integrity of the wall in relation to the target metal, and the propensity for cracking and crack nucleation within the crater wall.