Space debris

Since the commencement of space operations and the use of satellites for different purposes, a considerable number of items of space hardware have accumulated in earth orbit. Many of these have ceased to perform any useful function and can no longer be controlled in any way from the ground. The continuing accumulation of such objects is a risk to future satellite and space operations (ranging from actual collision to interference between transmissions or obstruction of data transmission).

In 1996 there were approximately 20,000 known items of space junk derived from exploded satellites and discarded rockets. Most pieces are about the size of a medicinal tablet, but at they speed they travel could have the effect of a small bomb if they struck a new satellite. Because elliptical orbits are the norm, the probability of junk hitting from any direction becomes significant (despite the vastness of space); junk in the lower part of its orbit is the most dangerous.