Mariner 1 spacecraft. Technicians prepare Mariner 1, the first American spacecraft intended to explore Venus. After a 58 million-kilometre journey, Mariner 1 was to use six instruments to study the temperature, atmosphere, cloud cover, magnetic field and radiation environment of Venus. The spacecraft was 3 metres long, 1.5 metres wide and weighed 202 kilogrammes. It was launched by an Atlas-Agena rocket on 22 July 1962 from Cape Canaveral, Florida. An error in the flight guidance programming meant that the rocket veered off course immediately after launch and had to be destroyed.