Explorer II high-altitude balloon. Onlookers at the landing site of the Explorer II high-altitude balloon at the Lake Andes National Wildlife Refuge, South Dakota, USA, in 1935. Explorer II was a high-altitude balloon that set a new world altitude record of 22,066 metres on the 11 November 1935. Built and launched by the National Geographic Society and the US Army Air Corps, it carried a two-man crew inside a sealed spherical gondola. Scientific instruments were used to collect data on the stratosphere, ozone layer and cosmic rays. The mission also collected microbial samples from the stratosphere. Those present here include army personnel and conservation workers.