A crude, ancient, but effective ground to orbit defensive weapon. A deep hole with a nuclear bomb at the bottom is mostly with water. The water is covered with a cap. Large boulders are placed on top of the cap. When the nuclear bomb explodes, the water turns to steam and the boulders are pushed out at high velocity (typically 20 to 30 kilometres per second). The large boulders do not stay in the atmosphere long enough to melt or vapourize, are difficult to intercept, and will cause massive damage to any ship in orbit, or anything attempting to land on the planet.

IRL - The thunder cannon of the Imperial Concordant Universe was inspired by nuclear tests during 1957. During Operation Plumbbob, various nuclear devices were tested by the United States military. One of the test, known as Pascal-B, involved placing a nuclear device in a one hundred twenty metre deep bore hole. A steel cap, weighing nearly one tonne, was welded to the top of the bore hole, with the intent of containing the explosion. A high speed camera filmed the test. The explosion sent the steel cap hurtling through the air, and was visible in only one frame of the video. Calculations show that, in order to be visible in only one frame, the cap had to be going at least sixty seven kilometres per second. Further calculations show that it (probably) did not spend enough time in the atmosphere to vapourize.