Word: asteroids
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Less controversial was the proposal that terrestrial defenders should know the exact nature of their target before acting. Responding early to a worrisome asteroid, they would send a "precursor mission," an instrumented spacecraft, to fly by or orbit the object and determine its size, shape and composition. One such "practice" mission, code-named Clementine, has already been budgeted by the Defense Department in coordination with NASA. It will fly an instrument package past the approaching asteroid Geographos in 1994 to test the kind of sensors and navigational devices that someday may be needed to help cope with a real threat...
Once the nature of the approaching object is determined, explains physicist Edward Tagliaferri, a U.S. space program consultant, "it becomes easier to decide if you want a standoff explosion, a surface explosion or a subsurface explosion," If the asteroid or comet is small, it can be vaporized with a subsurface explosion, but for larger bodies, says Tagliaferri, "you'll probably have to nudge them into a new orbit." For an asteroid consisting largely of iron, he says, "you'd probably want to have a surface explosion...
...attacking a large comet or stony asteroid, however, the interceptors would have to take care not to blast their quarry into many large chunks, each of which would be a potential city killer. One way of avoiding that, workshop scientists suggested, is to use the neutron bomb, a weapon that delivers most of its energy in the form of speeding neutrons rather than an explosive blast. The neutron warhead would be detonated when the missile approached to about a distance equal to the radius of the asteroid. "The neutrons penetrate deeply into the near side of the asteroid," Canavan explains...
...film in the observatory darkroom, he turns the negatives over to Carolyn, who scans each set of two under her stereo microscope. If anything has moved against the background of fixed stars during the 40-min. interval, it appears to float in the eyepiece. If so, it is an asteroid or comet and might someday present a threat...
Gene sensed that threat early in his career. Looking at the moon while a graduate student at Princeton, he was convinced that it had been pockmarked not by explosive volcanism, as many geologists then thought, but by asteroid impacts. If that was true, he felt, Earth, a much larger target, must have been heavily bombarded too. For his Ph.D. thesis, Shoemaker prepared a & geologic map of Meteor Crater in Arizona, and in the process confirmed that it had resulted from an impact...