But there are a few disadvantages with this laser heating method. Furthermore, laser beams, while nominally parallel, may not be sufficiently so over tens of millions of miles. The great distances involved would cause laser beam spreading which in turn reduces heat concentration. Therefore, the only effective method for using lasers is at close proximity. In addition, accurate aiming also poses a problem.
More problems arise when the laser beam has to target a moving object.
The laser approach also needs about 10-15 years to work effectively because of the lack of concentration of the heat from the laser as it is transmitted over such a large distance in space. One proposed idea for better targeting is to use a laser beam source stationed in earth orbit that would work on objects which remained at a certain 'constant' distance from Earth. Even so, precautionary measures would need to be taken to ensure the path the laser takes while shooting at the moving asteroid does not cross the Earth's surface. Laser beams of such high power can cause severe damage to the very planet it is trying to protect. American Professor Jay Melosh and Russian professor Ivan Nemchinov have also proposed launching a mirrored aluminum sail-like satellite into an orbit that tracks dangerous asteroids.