|The Pioneers were tiny, weighing only about 6 kilograms (about 13 pounds). In order to build spacecraft to fly to other planets, JPL embarked on the design of significantly larger craft. This series of spacecraft was called Mariner, and Venus was the first target.
At that time, many scientists thought Venus might be a slightly warmer Earth, with conditions like those on Earth when the dinosaurs lived. NASA's Cape Canaveral facility (now Kennedy Space Center ) launched the first Mariner spacecraft toward Venus on July 22, 1962, but the launch vehicle's guidance system failed. The range safety officer blew up the spacecraft about five minutes into flight.
First Planetary Success
Thirty-five days later, on Aug. 27, 1962, JPL sent an identical copy of Mariner 1 towards Venus. Mariner 2 became the Lab's first successful planetary mission. The spacecraft made its closest approach on December 14, 1962, performing a 'flyby' of Venus but intentionally not going into orbit.
Mariner 2 confirmed that Venus is incredibly hot. With a surface temperature exceeding 400 degrees Celsius (752 degrees Fahrenheit), and a surface pressure more than 300 times that found on Earth, Venus cannot support any kind of life like ours.
Mariners 3 and 4 were built to study Mars. Mariner 5 returned to Venus and, equipped with a different instrument suite than Mariner 2, carried out the second flyby of the planet on October 19, 1967.
Mariner 10, also known as Mariner-Venus-Mercury, performed a flyby of Venus on February 5, 1974. It then used a 'gravity assist' from Venus to visit Mercury, the closest planet to the sun. JPL navigators directed the spacecraft into an orbit that let it fly by Mercury three times between 1974 and 1975.