Word: orbit
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Still, the very notion of having high-megaton missiles at the ready, either on Earth or in orbit, was unsettling to many at the workshop, who feared that they could be turned against fellow humans rather than cosmic interlopers. They simply "did not want to talk about very large amounts of energy," says Canavan. "And therefore they wanted to ignore the problem." Some suggested heatedly, in leaks to the press, that pro-nuclear Star Wars scientists, frustrated by the down-sizing of their projects, were using the asteroid and comet threat as an excuse for revitalizing their jobs...
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...
...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...
...distance equal to the radius of the asteroid. "The neutrons penetrate deeply into the near side of the asteroid," Canavan explains. "They heat and vaporize the material, which expands at a high velocity and blows out of the side of the asteroid," thrusting it into a new, non-threatening orbit...
...intruders they watch for are Earth-crossing asteroids, giant rocks that have strayed from their neighborhood between the orbits of Mars and Jupiter and periodically pass close to Earth -- and sometimes smash into it. The vigil has paid off. Over the years, the couple have discovered more than 300 asteroids, some of which they have named after their children, grandchildren and in-laws. About 10% of their discoveries are ECAs, but none is currently in an orbit that puts it on a collision course with the earth. Still, the Shoemakers keep looking: lurking somewhere out there may be a hulk...