1950s-70s USA and Russia philatelic covers that are related to the early satellites development, manned and unmanned spaceflights to the moon.
1963-04-02 USSR Luna 4
Luna 4, launched on 2 April 1963 by the Soviet Union, was believed to be an attempt to soft land on the moon. Its engine failed to fire for a trajectory correction, so the spacecraft failed to reach the moon. Contact was lost after it past within 9,300 kilometers (5,780 miles) of the moon.