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The Growing Hazard of Artificial Space Debris

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By Tom Logsdon

Venture out into your backyard with a good pair of binoculars and you will get an opportunity to study the destructive potential of hypervelocity impacts. Many of the biggest lunar craters are rimmed with ragged white spokes formed eons ago when lunar subsoil was hurled radially outward by huge meteorites slamming into the surface of the moon. The average impact velocity of those savagely energetic projectiles has been estimated at 44,000 mi/hr.

Now swivel your binoculars gently across the evening sky, and you can uncover solid evidence for the population explosion of space debris whirling around the earth. Look toward the southwest as the sun begins to sink below the horizon. Four or five times every hour you will spot at least one orbiting object shimmering in the light of the setting sun. Now wait an hour or two and notice the number of stars visible to the naked eye. If the sky is dark and clear, and there are no city lights to create background glare, you should be able to see about 3000 stars--roughly half the number of objects now orbiting in one hemisphere. At this moment, space-age technicians at North American Air Defense (NORAD) are tracking more than 7000 objects whirling around the earth including hundreds of operational satellites, plus a much larger number of spent rockets, dead or dying space vehicles, shrouds, clamps, fasteners, and even Ed White's silver glove, which came off during his first walk in space.

Each year about 800 new objects are added, and roughly half that number plunge back down toward earth. Fortunately, most of them burn up before they impact the ground. Objects as small as soccer balls can be tracked by NORAD radars, but much smaller and lighter fragments can present a hazard to travelers in space. Because of their savage velocities, even a space debris fragment as small as a garden pea can damage an artificial satellite. Experts estimate that the total number of objects of destructive size is at least 20,000, perhaps substantially more.

Sixty percent of the trackable objects in NORAD's inventory have been produced by violent explosions in space, nearly 100 of which are known to have occurred. During the Cold War Russian scientists found a way to blow up enemy satellites. Their "killer satellites," big, deadly sawed-off shotguns, created one quarter of the explosions when they tested their space-age killer satellites against targets they launched into space. Spaceborne explosions also occurred when propellant tanks on American upper-stage rockets suddenly raptured. A few of these rockets were believed to be dead in space for 3 years or more before they exploded. According to industry rumors, early Soviet astronauts may have further aggravated the space debris problem by tossing garbage out of their manned space stations. NORAD's radar imaging devices are not sensitive enough to make a positive identification, but Russian watermelon rinds may be intermingled with other spaceborne objects our military technicians have observed streaking across their radar screens.

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