Depending on their orbital progress, Venus or Mars may be the closest planet to Earth at any given time. The distance between Venus and Earth varies between 24 and 162 million miles, and the distance between Earth and Mars varies between 34 and 250 million miles.
As the Apollo program was winding down in the 1970s, NASA came up with multiple proposals to use leftover Saturn hardware. One theoretical mission involved sending astronauts on a flyby of Venus, adapting a Saturn V upper stage similar to the later plans for Skylab. The mission would have taken advantage of the two planets' orbital proximity in 1973 to send a crew within 3,000 miles of the planet's surface for a brief examination.