Space ExplorationThe investigation of physical conditions in space and on stars, planets, and other celestial bodies through the use of artificial satellites, space probes, and spacecraft with human crews. The quest for greater knowledge and understanding—as well as Cold War rivalry between the United States and the Soviet Union—fueled the modern space race in both unmanned and manned spacecraft, but humans have acknowledged the powers of the solar system since prehistoric times. Advanced technologies, and an increasing spirit of private enterprise, open possibilities for new adventures and frontiers.