They are a kinetic energy device like the railgun, but instead of using electricity to achieve destructive velocities, they use gravity. The still-hypothetical system would be comprised of two satellites in orbit around the Earth. One would house the communications and targeting hardware, while the other would house the rods themselves, each up to a foot in diameter and twenty feet long. To fire, they would simply be released and allowed to fall back to Earth (with a bit of remote guidance). By the time they reached the surface, they'd be traveling at a speed of 36,000 feet per second and carry the destructive force of a nuclear warhead, only with none of the radioactive fallout.
!!! ... !!! Dropping telephone poles on people. From Space! Damn.
