Sun gun

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 8,200 kilometres (5,100 mi) above Earth. The scientists calculated that a huge reflector, made of metallic sodium and with an area of 9 square kilometres (900 ha; 3.5 mi2), 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. Evidence that Japan was also attempting to develop a death ray was uncovered by American forces. 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.