Impact crater. Damage to an aluminium sheet caused during research into high-velocity small particle damage to satellites. A nylon plug weighing 79 milligrams was fired at a double aluminium sheet at 4.89 kilometres per second in a vacuum. This crater is on the second sheet. The smaller craters surrounding the central one were caused by flying shards from the first aluminium sheet. From this research, it was found that two separate sheets of aluminium provide better protection than one of double thickness. Protecting satellites from impact damage is very important. As well as dust, there is an increasing amount of space junk" in orbit from previous missions."