The Apollo moon missions were a 21st-century idea that was slipped into the 20th century, said former astronaut Eugene Cernan in his 1999 book The Last Man on the Moon (St. Martin's Press). In the 1970s, soon after Cernan and his Apollo 17 crew completed the last moon mission of the 20th century, NASA developed the ferrylike space shuttle that has since dominated the U.S. space fleet. The shuttle was not intended to fly further than the distance required to orbit Earth, so there was no need to consider the health risks of years-long journeys into outer space.
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