9 August

1975:On 9 August 1975, ESA launched COS-B. COS-B was the first ESA mission to study gamma-ray sources. Its results created a catalogue of these sources, known as the 2CG catalogue, and a complete gamma-ray map of the disc of our Galaxy, the Milky Way.

Cos-B, one of the most successful space missions ever, had no optical telescopes or complicated scientific instrumentation (though the central spark chamber was a significant technical achievement). It had one function - pointing in the direction of a star or other object and measuring its gamma-ray emissions.