Monitoring and Controlling Debris in Space; August 1998; Scientific American Magazine; by Johnson; 6 Page(s)

Since the space age began four decades ago, rockets have lifted more than 20,000 metric tons of material into orbit. Today 4,500 tons remain in the form of nearly 10,000 "resident space objects," only 5 percent of which are functioning spacecraft. These objects are just the large ones that military radars and telescopes can track. Of increasing interest to spacecraft operators are the millions of smaller, untrackable scraps scattered into orbits throughout near-Earth space, from only a few hundred kilometers to more than 40,000 kilometers (25,000 miles) above the surface of the planet.

If Earth¿s tiny attendants moved like the hordes of miniature moons around Jupiter or Saturn, they would be a thing of beauty. The rings of the giant planets are finely orchestrated; their constituent rocks and chunks of ice orbit in well-behaved patterns, and collisions between them occur at gentle velocities. But Earth¿s artificial satellites resemble angry bees around a beehive, seeming to move randomly in all directions. The population density of satellites is fairly low; the region around Earth is still a vacuum by any terrestrial standard. But the haphazard motions of the swarm lead to huge relative velocities when objects accidentally collide. A collision with a one-centimeter pebble can destroy a spacecraft. Even a single one-millimeter grain could wreck a mission.