Explorer 11 (S 15)

Explorer 11, also known as S 15, was launched for the purpose of detecting the sources of high-energy gamma rays. In addition to detecting gamma rays, Explorer 11 was designed to map their direction with an emphasis on the plane of the galaxy, the galactic center, the sun, and other known radio noise sources; to relate the measurements to the cosmic-ray flux density and the density of interstellar matter; and finally, to measure the high-energy gamma-ray albedo of the earth's atmosphere.