Could you say more about space junk as an environmental problem?

Space debris are a big problem. There are literally hundreds of thousands, even millions of particles in orbit that are a millimeter or larger. These provide a constant source of trouble for astronauts and spacecraft, and can be lethal if direct impacts occur. The above image shows the extend of the current debris cloud. Space shuttles nearly always return to ground with some impacts to their bulkhead. These are small millimeter-sized scars, but in one case a forward viewing window was badly cratered by a collision with a piece of debris.

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