Any of a series of unmanned probes launched from 1961 to 1965 by NASA .
The project was NASA's earliest attempt to explore the Moon 's surface. Ranger 4 (1962) became the first U.S. spacecraft to hit the Moon, crash-landing on its surface as planned. The last three probes in the series (1964–65) sent more than 17,000 high-resolution photographs of the Moon before crashing. See also Luna ; Pioneer ; Surveyor .