1950s-70s USA and Russia philatelic covers that are related to the early satellites development, manned and unmanned spaceflights to the moon.
1968-01-07 USA Surveyor 7
Surveyor 7 landed in the lunar highlands near the crater Tycho. Devices were carried onboard to analyze chemically the material scooped out. Scientists used the scoop on the spacecraft to "weigh" lunar rocks, based on how much current was needed to lift each rock. Images sent back indicated some of the lunar rocks had been molten at some time in their history. The mission was successfully completed on 21 February 1968.