U.S. Unstaffed Planetary and Lunar Programs

Updated May 8, 2019 | Infoplease Staff

Lunar Orbiter. Series of spacecraft designed to orbit the Moon, taking pictures and obtaining data in support of the subsequent staffed Apollo landings. The U.S. launched five Lunar Orbiters between Aug. 10, 1966, and Aug. 2, 1967.

Mariner. Designation for a series of spacecraft designed to fly past or orbit the planets, particularly Mercury, Venus, and Mars. Mariners provided the early information on Venus and Mars. Mariner 9, orbiting Mars in 1971, returned the most revealing photographs of that planet and helped pave the way for a Viking landing in 1976. Mariner 10 explored Venus and Mercury in 1973 and was the first probe to use a planet's gravity to propel it toward another.

Pioneer. Designation for the United States' first series of sophisticated interplanetary spacecraft. Pioneers10 and 11 reached Jupiter in 1973 and 1974 and continued on to explore Saturn and the other outer planets. Pioneer 11, renamed Pioneer Saturn, examined the Saturn system in Sept. 1979. Significant discoveries were the finding of a small new moon and a narrow new ring. In 1986, Pioneer 10 was the first man-made object to escape the solar system. Pioneer Venus 1 and 2 reached Venus in 1978 and provided detailed information about that planet's surface and atmosphere.

Ranger. NASA's earliest Moon-exploration program. Spacecraft were designed for a crash landing on the Moon, taking pictures and returning scientific data up to the moment of impact. Provided the first close-up views of the lunar surface. The Rangers provided more than 17,000 close-up pictures, giving us more information about the Moon in a few years than in all the time that had gone before.

Surveyor. Series of unstaffed spacecraft designed to land gently on the Moon and provide information on the surface in preparation for the staffed lunar landings. Surveyor's legs were instrumented to return data on the surface hardness of the Moon. Surveyor dispelled the fear that Apollo spacecraft might sink several feet or more into the lunar dust.

Viking. Designation for two spacecraft designed to conduct detailed scientific examination of the planet Mars, including a search for life. Viking 1 landed on July 20, 1976; Viking 2, Sept. 3, 1976. More was learned about the red planet in a few short months than in all previous missions, but the question of whether there is life on Mars remains unresolved.