NASA ‘Echo 1a’, the first passive communications satellite experiment (via sRGB)
Wiki: “Echo 1 was a passive communications satellite: it functioned as a reflector, not a transmitter. After it was placed in a low orbit of the Earth, a signal would be relayed to Echo, reflected or bounced off its surface, then returned to Earth. Echo 1 was visible to the eye because of its shiny surface, but also because of its low orbit; it would appear from below one side of the horizon, cross the sky, then disappear below the opposite horizon after crossing the sky, as happens with all LEO satellites. The spacecraft was nicknamed a ‘satelloon’ by those involved in the project.”
See also: Jeff Koons ‘Rabbit’ 1986
Correction: This one is actually the 1966 NASA project PAGEOS