1950s-70s USA and Russia philatelic covers that are related to the early satellites development, manned and unmanned spaceflights to the moon.
1959-01-02 USSR Luna 1
The first successful lunar spacecraft was the Soviet Union Luna 1 (or Mechta), placed on a fly-by trajectory in January 1959. Launched on 2 January 1959, Luna 1 missed the moon and went into a solar orbit. However, the spacecraft did provide some scientific data when it released a sodium vapor cloud 70,000 miles from earth that allowed scientists to study interplanetary gases.