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Hazardous Encounters with Orbital Space Debris Patch

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By Tom Logsdon

On July 2, 1982, during the final day of their mission, astronauts Ken Mattingly and Henry Hartsfield, riding the space shuttle Columbia, flew uncomfortably close to a spent Russian Intercosmos rocket high above the northwester coast of Australia. By coincidence, that same region of space had experienced an earlier encounter with orbiting space debris when America's Skylab crashed in the outback in 1979. Astronauts Mattingly and Hartsfield were warned in advance, but they could not catch a glimpse of the big Intercosmos rocket as it whizzed by their spacecraft at 7000 mi/h.

Six months later, Russia's Cosmos 1402 abruptly slammed into the earth. Like its sister ship Cosmos 954, it was a spy satellite -- powered by a nuclear reactor fueled with radioactive uranium. But, unlike its sister ship, Cosmos 954 crashed to earth on the sovereign territory of an innocent nation. In 1978, when Cosmos954 fell in northern Canada, the Canadian government spent $6million cleaning up the mess. Later, with some resistance, the Soviet Union reimbursed Canada for half that amount.

Military engineers track approximately 7000 objects in space as big as a soccer ball or bigger. A few hundred of them are functioning satellites. The rest are a varied lot: spent rockets, protective shrouds, clamps, fasteners, jagged fragments from space vehicle explosions, even an astronaut's silver glove. In addition to the 7000 objects of trackable size, tens of thousands of smaller ones are presently swarming around our planet.

These orbiting fragments are hazardous, but not to the people living on the ground below. On the average, human beings occupy the surface of the earth, only 17 tiny bodies per square mile. The Skylab was among the largest reentry bodies ever to plunge through the atmosphere, but scientific calculations indicated that the probability of any specific individual being hit by Skylab debris was only about 1 in 200 billion.

Actually, no calculations at all are needed to demonstrate that the probability of being bashed by orbital space debris is extremely small. More than 1500 large, hypervelocity meteorites are known to have plunged through the atmosphere and hit the earth -- roughly 8 per year for the past 200 years. Many of them shattered into smaller fragments on reentry, but not one single human being's death certificate reads "death by meteorite." And yet, if we go back far enough into the dim shadows of history, we may find at least one reliable reference to human injury and death caused by falling meteorites. It is buried in the bible's book of Joshua, in a passage describing how terrified soldiers fleeing from battle were killed by "stones falling from heaven."

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