The United States and the Soviet Union began
exploring space in the 1950s. Both nations strived to be the first
to get spacecraft into Earth orbit and to the Moon. Some efforts
succeeded. Some failed. As successes mounted, momentum built for
attempting the next great leap: going to another planet.
A robot named Mariner 2,
about twice as tall and three times as heavy as a human adult, coasted
noiselessly past cloud-wrapped Venus on Dec. 14, 1962, and became
Earth's first emissary to successfully examine another planet up
close. NASA's Jet Propulsion Laboratory designed, built and operated
Mariner 2, which found that
Venus has cool clouds and a very hot surface.
A series of other JPL-managed Mariner missions in the 1960s and
early 1970s paid initial visits to Mars and Mercury plus follow-ups
to Venus and Mars. The first spacecraft to orbit another planet,
Mariner 9, discovered dry
riverbeds, massive volcanoes and vast canyons during its orbital
tour of Mars beginning Nov. 14, 1971. Besides its scientific discoveries,
the Mariner series built up expertise for planning and managing
future planetary exploration. Mariner
10, launched in 1973, visited two planets, pioneering the use
of "gravity-assist" maneuvers by using Venus' gravity
for a boost toward Mercury.
Other early JPL spacecraft inspected our own planet's Moon. The
Ranger series of crash landers and Surveyor series of soft landers
in the 1960s supplied detailed photographs and surface analysis
that scouted the way for the bootprints of Apollo astronauts.