Skylab's Fiery Fall

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A decade after the moon walk, a crash landing for a 77.5-ton giant

With varying degrees of fear, anger and fascination, but mostly with a detached kind of bemusement, the world this week awaits an unprecedented event: the fiery fall of the largest machine man has ever hurled into space. The American Sky lab vehicle, nine stories tall and weighing 77.5 tons, is expected to slip into the earth's upper atmosphere, then disintegrate into a celestial shower of flaming metal as spectacular as any of last week's Fourth of July fireworks displays. Somewhere, probably at sea, ten fragments, each weighing 1,000 Ibs. or more, will crash to earth at speeds of up to 270 m.p.h. with the force of a dying meteor. Thus will be observed, after a series of miscalculations, the tenth anniversary of man's proudest achievement in space, the walk on the moon.

Despite all their wondrous tracking stations, bristling with huge radar antennas and feeding the most advanced electronic computers, America's top military and civilian space scientists could not predict even roughly where Skylab would fall. Until the final hours, they could narrow the area of eventual impact only to a vast global band between 50° north latitude and 50° south latitude—a sweep of about 109 million sq. mi., or nearly 56% of the earth's area. Conceded Hal Sierra, one of the technicians monitoring Skylab's death throes from the Lyndon B. Johnson Space Center near Houston: "We're balancing on a knife edge—but we're not sure where the knife is."

Officials of the National Aeronautics and Space Administration, which conceived and launched Skylab six years ago, took comfort in the mathematics of probabilities. Some 500 fragments of the huge space workshop will be dispersed over an area 4,000 miles long and 100 miles wide, a scattering that the scientists call, with anthropomorphic archness, Skylab's "footprint." Moreover, on each of Skylab's 90-minute orbits of the earth, nearly 67 minutes, or 75%, is spent over water. What all that means, contend NASA'S statisticians, is that the chance of any remnant striking a human being is only 1 in 152; the probability of any specific person being struck is 1 in 600 billion—far less than the chance of being hit by a bolt of lightning or winning a lottery.

NASA, however, was not taking the potential danger at all lightly. One of the heaviest pieces of Skylab, a two-ton lead-lined vault used for film storage, is capable of digging a hole 5 ft. wide and 100 ft. deep. And within the band of Skylab's orbital paths lie some of the world's most populous areas, including all of the U.S., much of Europe, India and China. Indeed, the chance of debris falling in some city of at least 100,000 inhabitants is a sobering 1 in 7. Only 10% of the earth's inhabitants can be considered totally free of any risk from Skylab's metallic fallout.