It wasn’t an understatement when Neil Armstrong said he took a giant leap for mankind when upon taking his first step on the Moon. During the Apollo program, six crewed missions landed on the Moon (with a seventh, Apollo 13, famously making an emergency return to Earth without landing.) On those missions, twelve astronauts conducted an array of increasingly sophisticated studies of the Moon, yielding new scientific insights into the evolution of our celestial neighbor. Each mission explored new areas of the lunar surface and left behind nuclear-powered scientific instruments that continued to send data back to Earth years after the last astronaut left the Moon. However, the Apollo program ended in December 1972 with Apollo 17. Why did we stop?
For many citizens, beating the Soviet Union to the Moon ended the Space Race. Public support for expensive programs of human space exploration, never very high, declined considerably; enthusiasm was further eroded by the expense of the Vietnam War, the serious problems in the cities, and a growing sense of environmental crises. That disappointed space advocates who expected that Apollo would be the beginning of an era in which humans would move out into space, to bases on the Moon, space stations in Earth orbit, and landings on Mars.
Nevertheless, this overall shift to diminished support in public and political sentiment resulted in a modest program of post-Apollo human space activity. Two programs, using leftover Apollo rockets and spacecraft, symbolized this new era: Skylab and the Apollo-Soyuz Test Project.
Skylab, an experimental habitat built from the third stage of a Saturn V, was the first American space station. It was only intended as a temporary home in space. The longest mission, which ended in February 1974, lasted almost three months. Skylab was occupied by astronauts three times over 1973 and 1974, each time by a crew of three astronauts.
The Apollo-Soyuz Test Project (ASTP) marked a real and symbolic end to Apollo and the Space Race of the 1960s. To highlight reduced international tensions the United States and Soviet Union undertook, after years of intense rivalry, their first cooperative mission in space. In July 1975, an American and a Soviet spacecraft rendezvoused in space as a symbol of the two countries improved relations. The crews visited each other's spacecraft, shared meals, and worked on various tasks during several days together in space.
Now, after over 50 years, Americans are again preparing to send astronauts to the Moon.