Imagine three astronauts, 125 million miles from the Earth, talking to Mission Control with a four-minute time lag. They have seen nothing out their windows but stars in the blackness of space for the last 150 days. With a carefully timed burn, they slow into orbit around Venus, and as they loop around the planet, they get their first look at its thick cloud layer just 7,000 miles below.
It might sound like the plot of a science fiction movie, but in the late 1960s, NASA investigated missions that would send humans to Venus and Mars using Apollo-era technology. These missions would fly in the 1970s and 1980s to capitalize on what many expected would be a surge of interest in manned spaceflight after the Apollo lunar landings. They would be daring missions, but they would also be feasible with what was on hand.
For the rest of the story: http://arstechnica.com/science/2013/08/what-might-have-been-visiting-mars-and-venus-with-apollo-era-hardware/