Explorer II high-altitude balloon. Historical image of the Explorer II high-altitude balloon during its flight. Explorer II was a manned balloon launched on 11th November 1935. It reached a record altitude of 22,066 metres and carried a two man crew inside a sealed spherical gondola. It carried a number of scientific instruments carried on the gondola that returned useful information about the stratosphere. Here it is at 12,000 ft and is lowering an electrograph. Photographed in November 1935.