Mass is meaningless in regard to this small a body in space. As far as velocity, it is not trying to stop it head on, it is sideswiping it. A polypropylene riot shield will not stop a bullet, but if angled properly in can cause a deflection. Also keep in mind that while the Dart is small, it impacted at over 10,000 MPH. That is a LOT of velocity bought to a dead stop, to which the moonlet has to react, and there is very little if any inertia in space.My question is this. Do they seriously think they are going to significantly change an object on a collision course with earth? Considering the mass, possible composition and velocity has anyone calculated the velocity and mass required to alter the orbit. I doubt we have the capability to launch something heavy enough or fast enough to do any good, science fiction movies not withstanding.