Okay, to summarize this discussion: A radar would not be able to detect particles such as grains of sand or small rocks. Therefore I suppose you need a powerful laser in the front of the spacecraft to heat them and break them into molecules or plasma. It would have to be turned on at all times because you cannot detect these particles.
Even atoms and molecules would be large enough to cause damage. So you need to push them out of the way. I suppose the only way to do this with known science is to ionize them and then use a magnetic field to push them out of the way. I do not know if you can ionize particles from a long distance away. It would have to be very long! Something like a science fiction "force field" would probably be the best solution. I have no idea whether such a thing is possible.
