Final answer:
The Space Shuttle program, operating from 1981 to 2011, was envisioned to make space travel more routine and economical with reusable components. However, it remained costly due to the need for human operation and was retired after 135 launches, ending U.S. human space launch capacity. Figures like Van Allen advocated for a balance between human and robotic space exploration.
Step-by-step explanation:
The Space Shuttle program, which operated from 1981 to 2011, was a significant period in American space history. The program aimed to make space travel routine and included features like reusable solid fuel boosters. Despite the vision of economic and routine space travel, the shuttle program proved to be costly due to the need for human operation. Human spaceflight was necessary for missions such as the repair of the Hubble Space Telescope; however, it was suggested by figures such as Van Allen that NASA should not focus solely on manned missions but also invest in robotic spacecraft. After 135 launches, two of which tragically ended in disaster, the shuttle was retired, and this marked the end of America's capability to launch humans into space using its own vehicles. The Space Shuttle's unique feature of reusability, including the craft itself and the solid fuel boosters, did not result in the anticipated cost savings when compared to unmanned, expendable rockets. The shuttle era was punctuated by awe-inspiring moments, such as in Figure 2.29, showing the Endeavour lifting off from the Kennedy Space Center or the weightlessness experienced by astronauts shown in Figure 24.5, where Shane Kimbrough and Sandra Magnus are surrounded by floating fruit aboard the shuttle. This lack of apparent gravity is due to the shuttle's free-fall state while orbiting Earth.