When the space shuttle was conceived in the 1970's, the dream of engineers was to create a new kind of spacecraft—one that could carry people and cargo into orbit, return to Earth, and then be used again repeatedly. They succeeded, but only partially.

In 1997, the National Aeronautics and Space Administration (NASA) and private aerospace companies were working to develop a space-launch vehicle that would operate more like an airplane. They envisioned a spacecraft that not only could be used repeatedly but would also be reliable and efficient enough to fly more frequently and at far less cost than the shuttle.