The Air Force Space Command NORAD radar system tracks about 7,000 objects larger than 10 centimeters, but this is only the tip of the iceberg. The Arecibo radio telescope conducted a limited survey, and from the number of radar returns from objects larger than one centimeter identified over 150,000 objects in orbit. NORAD tracks a total of 100,000 individual objects from the size of a glove or larger. The Arecibo data suggest there are about one million objects larger than 2 millimeters. When you include things like paint chips and other sub-millimeter objects that are untrackable, the numbers may be as large as one hundred billion.
The Space Shuttle collided with a paint fleck from a previous mission or rocket launch and this chipped the front window leaving a crater several millimeters across. A 1-centimeter object moving with a relative speed of 17,000 kilometers/hour would deliver as much energy as a small hand grenade. The International Space Station has a front bumper that will try to protect its most vulnerable parts from the numerous objects of millimeter-size, but larger objects will be a rare, but ever-present problem capable of producing breaches in the pressurized parts of the station.
For more information try the European Space Agency debris site. There is a Space Debris resource page at the Aerospace Corporation site. Also, there were over 1000 matches to 'space debris' found on Alta Vista. There are also articles in the print media:
Eberhart, J. "Tallying Orbital Trash." Science News 138, 29, July 14, 1990.
Goldstein, R. M. and Goldstein, S. J. Jr. "Flux of Millimetric Space Debris." Astron. J. 110, 1392-1396, 1995.
Goldstein, S. J. Jr. and Goldstein, R. M. "Some Properties of Millimetric Space Debris." Astron. J. 107, 367-371,
1994.
Copyright 1997 Dr. Sten Odenwald
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