RFGs are just a subclass of "kinetic impact weapons", which are _definitely_ feasible. RFGs are rod-shaped to minimize air resistance during re-entry. Tungsten

RFGs are just a subclass of "kinetic impact weapons", which are _definitely_ feasible. RFGs are rod-shaped to minimize air resistance during re-entry. Tungsten is the material they're most associated with, but DU would likely work just fine as well. A (relatively) small, tungsten rod can be launched by braking from a parking orbit which would mean extremely little in the way of detectable activity. Even if it were detected... it's already at apogee, already at orbital speed, and already on a virtually unstoppable course to impact. To take this a step further - realistically, Elon Musk is on the cusp of being the most powerful man the world has ever seen. Once SpaceX has a semi-permanent presence in orbit and beyond, he would have the practical ability to launch attacks anywhere on Earth with a destructive potential on par with nuclear weapons.