sions to the lunar surface—perhaps not as dramatic as astronautics walking on the surface, but certainly just as scientifically valuable, demonstrating the utility and excitement of robots traveling beyond Earth and exploring the surface of new worlds under control of humans on Earth.
We did set foot on the Moon almost exactly as Von Braun had originally envisioned, but not on Mars.
After Apollo, the political will in the United States evaporated. In 1972 the United States abandoned the Apollo program and the future promise of lunar bases and human flights to Mars. The human space exploration enterprise retreated to Earth and was resigned to remain in Earth orbit.
While human space exploration languished after 1972, robotic exploration flourished (see Figures 3.3, 3.4, 3.5, and 3.6), and that has kept our dreams alive. Humans may not have exploded out into the solar system, but our robots certainly have. We have leapt off the surface of our home planet and sent robotic extensions of our eyes, ears, noses, arms, and legs to the far reaches of the solar system. Our robotic explorers go where we cannot go because of the limitations of our bodies, and they go where we cannot yet go because of the limitations of our own vision and will.
Since the abandonment of human exploration of space beyond Earth, robotic spacecraft have surveyed the solar system from Mercury to beyond Pluto; orbited Venus, Mars, Jupiter and Saturn; and landed on the Moon, Venus, Mars, and Titan to show us the bizarre surfaces of exotic new worlds. In 1957 these places could only be imagined, and traveling to them was in the realm of science fiction. Today, the solar system has become our backyard.