Explorer 6, or S-2, was an American satellite launched on August 7, 1959. It was a small, spheroidal satellite designed to study trapped radiation of various energies, galactic cosmic rays, geomagnetism, radio propagation in the upper atmosphere, and the flux of micrometeorites. It also tested a scanning device designed for photographing the Earth's cloud cover, and transmitted the first pictures of Earth from orbit. In 1959 an anti-satellite missile test of the Bold Orion rocket used Explorer 6 as a target. The missile successfully passed within 6.4 kilometers (4.0 mi) of the satellite.