The Apollo program landed 12 people on the moon over four years.
The Apollo program landed 12 people on the moon over four years.

In the 1960s, the United States and the Soviet Union were engaged in a global struggle for economic, ideological and political preeminence. When the Soviets launched Yuri Gagarin into orbit around the Earth, it pushed the United States to respond -- first by trying to match the Soviets, then by pledging to literally fly past them and be first to land on the moon. That drive culminated in the visit of six crews of American astronauts to the surface of the moon. Since then, there have been 18 robotic missions to the moon, but humans have not set foot there again.

Public Relations and Prestige

President John F. Kennedy's special assistant for science and technology believed human space flight was too risky, and that robotic exploration was a better option. He believed that putting humans in space only had value as a public relations move. After Yuri Gagarin orbited the Earth, the United States needed good press. In his speech announcing the United States' commitment to landing a man on the moon, Kennedy acknowledged the propaganda value of the move, citing "the impact of this adventure on the minds of men everywhere, who are attempting to make a determination of which road they should take." Here the two roads represented the choice between a communist dictatorship and a capitalist republic. The world is much different today, and that choice is no longer a primary concern.

Scientific Goals

In the years since last manned launch, the robot missions have satisfied the country's moon research goals. Although the public relations value of crewed missions to the moon was the predominant driver for the political will that pushed the Apollo program, the missions also had scientific goals. One of the preeminent questions of the time was about the origin and structure of the moon. The Apollo astronauts set up tests on the lunar surface and returned 400 kilograms of mineral samples that showed that Earth and moon rocks share a common heritage, but that they had been separated a few billion years ago. The samples also provided evidence that the moon was once geologically active, with lots of flowing lava, but that the moon is now very quiet, geologically. More than forty years after the Apollo missions, scientists continue to learn new things from the samples the astronauts returned — and even more from robotic probes to the moon.

The Cost

The Apollo program ended up costing $25 billion, which is equivalent to about $140 billion dollars today. This is equivalent to eight years of NASA's total current budget. To spend that kind of money on a single program would require a solid case that would compel agreement from elected officials in every part of the political spectrum. Today, it's difficult to imagine a combination of reasons that would drive a majority of citizens -- and their elected representatives -- to accept such a cost. And that $140 billion is just to duplicate the Apollo program. A new moon landing program would almost certainly cost much more.

Modernized Space Programs

The country has reset its space exploration goals in the years since the manned moon launches. With the end of the Cold War, there is no compelling political reason driving additional human exploration of the moon. One of the goals of the Apollo program was to prove it could be done, and that mission was accomplished. So a new mission to the moon would need to have significantly greater goals than the Apollo program. Greater goals mean an even higher cost, so the problem becomes even worse, because we would need to have a compelling reason to spend those billions. So far, such a reason has not been articulated. Much more compelling reasons have been offered for the country's Mars and space station programs, making them a much more attractive expenditure of funds.