DE-STAR has not been realized as yet, but theoretically a DE-STAR system would not reduce all sized asteroids to space rubble, only the smaller ones, but when it didn't destroy them, it would be capable of steering the comet, asteroid, threatening body out of our orbit. It is expected that the DE-STAR system would be capable of 1.4 megatons of energy a day which would in turn be capable of eroding an asteroid of 500 meters in approximately a year. This is all according to Hughes and Lubin, two physicists at California’s Polytechnic State University.
The sizes of the asteroids it would be able to destroy could be increased as the size of the system were increased. AND even better, it has other possible uses. One would be aiding a properly shielded spaceship to accomplish interplanetary travel, perhaps aid in the determination of the composition of an asteroid or other heavenly body. (maybe help Asteroid mining?)
According to Hughes this is not some SciFI dream, but rather can be made mostly from existing systems. Basically this system would channel solar power into a phased array of lasers which would then in turn be utilized against the offending asteroid.
Unfortunately the world will most likely have to agree that the threat against the world from asteroids outweighs fears of using such a saving object as a weapon against Earth. International laws as far back as 1967, 1971, and many more recently such as 2002 prevent the development of such devices. The UN maintains a legal vote which consistently bans deployment of space weapons, but in light of recent events from Russia to San Francisco to Florida, it is likely this needs to be revisited.
Seeing as asteroids are a threat to all of earth, perhaps all of earth should be involved in this project with it necessitating all governments to activate it...Working together as one people, one planet, mankind, we can accomplish so much more. Take a page out of the book Sanacion: The Black Hole Mission. .