Sun gun

The sun gun or heliobeam is a theoretical orbital weapon, which makes use of a concave mirror mounted on a satellite, to concentrate sunlight onto a small area at the Earth's surface, destroying targets or killing through heat.

History
In 1929, the German physicist Hermann Oberth developed plans for a space station from which a 100-metre-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 8200 km above Earth. The scientists calculated that a huge reflector, made of metallic sodium and with an area of 9 sqkm, could produce enough focused heat to make an ocean boil or burn a city. After being questioned by American officers, the Germans claimed that the sun gun could be completed within 50 or 100 years.

With the deployment and validation of satellite mega-constellations, their use as a sun gun has also been proposed. Instead of a vast individual mirror, hundreds of low cost reflectors could in theory be synchronized to concentrate solar irradiance and aim it at a target.