Prompt's TechBlog

When former US president Ronald Reagan made his famous 'Star Wars' speech back in 1983, he talked about a global network of defensive weaponry capable of intercepting and destroying cold war strategic ballistic missiles before they reached American allied soil. The world gasped, and half expected hundred of thousands of cranes to start hoisting space-age missile installations into the sky.
Fortunately, although often misguided and misled, Reagan was quite correct when he also said in the same speech: "I know this is a formidable, technical task, and one that may not be accomplished before the end of the century." Or indeed at all, not that we'd ever know about it until it was too late anyway...
However, here and now, in 2006, and still in the good ol' US of A, two NASA astronauts HAVE figured out a way to create a real-life version of a Star Wars 'tractor beam', a more peacable George Lucas invention, which they believe could be used to keep asteroids from crashing into the Earth. Now that's more like it.
The idea is that simply by hovering near an asteroid for a year or two, a nice big spacecraft could use its own gravity to minutely slow the big rock's progress. Or speed it up. In this way, the tractor beam-craft could cause the rogue rock to miss Earth by a comfortable margin. But only if it gets to work some 20 or 30 years prior to impact.
The astronauts claim the design would only require a 'relatively small' 20-ton spacecraft powered by charged atomic ions, generated by an onboard nuclear reactor. With ordinary chemical fuel however: "you'd be talking about a spacecraft that's 20 to 40 times larger, and that kind of technology doesn't exist." Ah...