LDEF was an inexpensive satellite launched in 1984. Its sole purpose was to measure various aspects of the near-earth space environment, including atomic oxygen, radiation, orbital debris and meteoroids, among other things. Because of the Challenger tragedy, LDEF was forced to stay on orbit years longer than was originally intended, before finally being retrieved by STS-32 in 1990 and brought back to earth. The satellite has become a bottomless data source for hypervelocity impact research.
During its six years in space, LDEF was impacted millions of times. Some of the impacts were made by very tiny particles - particles so tiny, they were only visible under an electron microscope. Others were visible to the naked eye, like the one shown in the image at right. LDEF has been a valuable source of information about the meteoroid and orbital debris environment in near-earth orbit.
The Russian Space Station Mir has witnessed numerous impacts during its many years in orbit. Here are some photos of orbital debris impacts.