If we break asteroid into smaller pieces wouldn't that be enough? Small pieces won't reach surface of earth and won't cause any damage. > You shoot a little pu

If we break asteroid into smaller pieces wouldn't that be enough? Small pieces won't reach surface of earth and won't cause any damage. > You shoot a little pulse at the gravel pile and break a piece off and it may simply fly out into space, taking almost all the momentum with it and not affecting the bigger body at all. this is true for shooting with projectile, but not for vaporizing with laser. With laser you don't apply any external momentum to the asteroid, vapor small debris fly off the asteroid with some momentum because of expanding under heat, and remaining part gets same momentum in the other direction.