Later during World War II, a group of scientists at a research center in Hillersleben, Germany began to expand on Oberth’s idea of creating a superweapon that could utilise the Sun’s energy. This so-called 'Sun Gun' would be part of a space station 5,100 miles above Earth. They calculated that the use of a huge reflector could produce enough heat, if focused on certain area, could make an ocean boil or burn up a city. German physicists had already figured out the sun gun's necessary size (3½ sq. mi.) and composition (metallic sodium).
After being questioned by Allied officers, the Germans made it clear that the Sun Gun could be completed within 50 or 100 years. Lieutenant Colonel Keck later stated, We were impressed with their practical engineering minds, and their distaste for the fantastic. Being an engineer himself, he took the Germans' claim seriously.