From Popular Science

UC Santa Barbara physicist Philip M. Lubin and California Polytechnic State University San Luis Obispo researcher Gary B. Hughes have unveiled plans for DE-STAR (cough, cough), or Directed Energy Solar Targeting of Asteroids and exploRation. The system, they say, could slowly vaporize earth-bound rocks over the course of as much as a year. From a UC Santa Barbara news release (emphasis mine):

Described as a "directed energy orbital defense system," DE-STAR is designed to harness some of the power of the sun and convert it into a massive phased array of laser beams that can destroy, or evaporate, asteroids posing a potential threat to Earth. It is equally capable of changing an asteroid's orbit –– deflecting it away from Earth, or into the Sun –– and may also prove to be a valuable tool for assessing an asteroid's composition, enabling lucrative, rare-element mining. And it's entirely based on current essential technology.

The scientists went through several plans for a potential asteroid-zapper, all of varying sizes, including one about the size of the International Space Station, called DE-STAR 2, which could start to "nudge" an asteroid in a different direction. DE-STAR 4, at about 100 times the size of the ISS, could vaporize a 500-meter asteroid in a year. Here's the description for DE-STAR 6:

Larger still, DE-STAR 6 could enable interstellar travel by functioning as a massive, orbiting power source and propulsion system for spacecraft. It could propel a 10-ton spacecraft at near the speed of light, allowing interstellar exploration to become a reality without waiting for science fiction technology such as "warp drive" to come along, Lubin said.

I'm always a bit amused with any light-sail spaceship or power collectors that involve utilizing a focused beam of energy, or 'death ray', partially because of that old notion that scientists don't tend to think of military applications, which is reverse from my own anecdotal experience. Though I suppose there might be a habit of trying not draw too much attention to how the really cool new discovery that should be embraced and funded because it would let you 'have abundant cheap energy' would also be really cool at torching major cities into ash.

Note that the #6 doesn't mention how long it takes to vaporize an asteroid just make a brief mention near-light travel for a ten ton ship. Nobody designs a ten ton interstellar craft, only much lighter robot probes or much, much heavier manned ships so I'm guessing someone decided to shoehorn that one in there.

FYI, a ship moving at half the speed of light that weighed ten tons would have 112,500 petajoules of kinetic energy, and a 1 megaton nuclear warhead has... 4. The ship if it slammed into something would release about 26,000 1 megaton nukes worth of explosive damage and you'd end up using more than that to get the thing up to that speed even with a laser. Possibly more relevant, 112,500 petajoules is about 9 years worth of US power consumption. On the flip side, that is around the amount of energy Earth receives from the sun every ten minutes.

For those of you who are interested in plans for dealing with asteroids - which range from the traditional 'nuke it' to painting the things, wiki discusses it, and Discover Channel has a nice slideshow of options and you can google some more serious detailed site like the B612 Foundation or neoshield.net