The sun gun or heliobeam is a (still) theoretical orbital weapon, which makes use of a concave mirror mounted on a satellite, to concentrate rays from the sun on to a small area of the Earth’s surface, destroying targets or killing through heat.
In 1929, the German physicist Hermann Oberth developed plans for a space station from which a 100m-wide concave mirror could be used to reflect sunlight onto a concentrated point on the earth.
Later during World War II, a group of German scientists at the German Army Artillery proving grounds at Hillersleben began to expand on Oberth’s idea of creating a superweapon that could utilize the sun’s energy.
This so-called “sun gun” (Sonnengewehr) would be part of a space station 8,200 km above Earth. The scientists calculated that a huge reflector, made of metallic sodium and with an area of nine square km, could produce enough focused heat to make an ocean boil or burn a city.
Scientists themselves acknowledge that this idea was about 100 years ahead of its time. Which begs the question – how on Earth their bosses allowed them to spend precious time and effort on such fairy-tale projects?