Space stations have been a mainstay of human space exploration since the early 1970s. Of the many types of hardware that have been blasted into space-whether orbiting satellites, reusable transport vehicles such as the shuttle, or unmanned robotic probes making one-way journeys to distant planets and beyond-none possess the complexity, technological sophistication, or size of a space station. These qualities make space stations the workhorses of space exploration. They are highly valued as medical laboratories for learning about the effects of weightlessness on humans, platforms for astronomical studies of distant stars and galaxies, and observation posts for viewing and analyzing natural and human-caused phenomena on Earth.

The technological complexity of modern space stations took decades to develop. Today's International Space Station (ISS), the latest and most complex laboratory in space, is the beneficiary of research efforts dating back...