On 3 November 1973, the Mariner Venus/Mercury 1973 spacecraft -- also known as Mariner 10 -- was launched from Kennedy Space Center. It was the first spacecraft designed to use gravity assist. Three months after launch it flew by Venus, changed speed and trajectory, then crossed Mercury's orbit in March 1974.
This photo identifies various parts of the spacecraft and the science instruments, which were used to study the atmospheric, surface, and physical characteristics of Venus and Mercury. This was the sixth in the series of Mariner spacecraft that explored the inner planets beginning in 1962.