Sun gun

The sun gun or heliobeam was a theoretical orbital weapon that was researched by Nazi Germany during World War II.

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.

Development
Later during World War II, a group of German scientists at a research centre in Hillersleben began to expand on Oberth's idea of creating a superweapon that could utilize the sun's energy. This so-called "sun gun" would be part of a space station 5,100 miles above Earth. The scientists calculated that a huge reflector, made of metallic sodium and with an area of 3.5 square miles, could produce enough focused heat to make an ocean boil or burn a city. After being questioned by Allied officers, the Germans claimed that the sun gun could be completed within 50 or 100 years.