I am not sure about usefulness of kinetic impactors at near light speeds over long distances. Imagine you are in impactor frame of reference -- any particle of

I am not sure about usefulness of kinetic impactors at near light speeds over long distances. Imagine you are in impactor frame of reference -- any particle of dust it meets will cause tremendous damage to it regardless of what the impactor is built of (assuming our existing technology). It is in my opinion very likely that over long distances the impactor will just get converted to a shower of high energy particles over very large area.