1950s-70s USA and Russia philatelic covers that are related to the early satellites development, manned and unmanned spaceflights to the moon.
1966-08-10 USA Lunar Orbiter 1
After a 92 hour voyage, the first successful United States Lunar Orbiter entered into orbit around the moon on 14 August 1966. Lunar Orbiter 1 sent back high-quality images (by television) of over two million square miles of lunar surface, including the first detailed images of potential Apollo landing sites. On its 26th orbit of the moon, the first pictures were taken, developed, and stored. Electronic scanning and transmission to earth commenced on 18 August. After circling the Moon 527 times in 77 days, Lunar Orbiter 1 was deliberately crashed onto the moon's surface to prevent the possibility of its radio disturbing communications between earth and the Lunar Orbiter 2, whose launching was imminent.