On July 20, 1969, the people of Earth looked up and saw the Moon in a way they had never seen it before. It was the same Moon that humans had been observing in the sky since the dawn of their existence, but on that July evening, for the first time in history, two members of their own species walked on its surface. At that time it seemed that Neil Armstrong's "giant leap for mankind" would mark the beginning of a bold new era in the exploration of other worlds by humans.

In 1969, some people believed that human scientific colonies would be established on the lunar surface by the 1980s, and that a manned mission to Mars would surely be completed before the turn of the twenty-first century. By the end of 1972, a dozen humans would explore the surface of the Moon. However, 28 years later, as revelers around...