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.