And what would be the purpose of all this? For those who have never known the relentless urge to explore and discover, there is no answer. For those who have felt this urge, the answer is self-evident.
—Hermann Oberth, Man into Space, 1957
The rise of private-sector spaceflight and American billionaires pursuing their ambitions in space seems to be a new phenomenon. After the origin of space exploration as a government enterprise during the Cold War Space Age, entrepreneurs and individuals have become a new force on the scene and are increasingly the drivers behind some of the most prominent space activities. In the Cold War, the United States and the Soviet Union developed intercontinental ballistic missiles to deliver their nuclear warheads, creating the technology for satellites and spaceflight vehicles. The race into space then became an important dimension of the Cold War as the two superpowers competed vigorously to be the first to claim prestigious spaceflight achievements, culminating in an American victory with the successful expedition of Neil Armstrong and Buzz Aldrin to the surface of the Moon. After the unmatched success of the Apollo program, with no political need for further spectaculars, NASA was downsized, spaceflight was confined to low-Earth orbit, and further exploration was confined to robots. Since then, NASA spaceflight projects have continued to advance our knowledge of the solar system and the universe ...