1950s-70s USA and Russia philatelic covers that are related to the early satellites development, manned and unmanned spaceflights to the moon.
1965-07-18 USSR Zond 3
On 18 July 1965, the Russians launched Zond 3 which took a number of good quality photographs for its time as it flew by the far side of the moon, then transmitted the images back to Earth nine days later. After passing the moon, the spacecraft went into a solar orbit. It was believed that Zond 3 was initially designed as a companion spacecraft to Zond 2 to be launched to Mars during the 1964 launch window. However, the launch opportunity was missed, and Zond 3 was launched on a Mars trajectory as a spacecraft test. Zond 3 was the second spacecraft to view the far side of the moon.