Enos was the first chimpanzee astronaut, launched into space in 1961 as part of the U.S. space program. He was part of a series of tests to determine if primates could survive the rigors of spaceflight and pave the way for human astronauts. Enos was the first chimp to complete a successful orbital mission, orbiting the Earth twice before returning safely to Earth. His name is an acronym for 'Earth Orbital Navigator Satellite'.