"Mars is not just the next or most accessible human destination, it is the ultimate one," writes Louis Friedman, executive director emeritus of The Planetary Society. He says the concept of manned spaceflight is progressing so slowly, and robotic developments so swiftly, that Mars will be the first and last planet humans set foot on.
"By the time human spaceflight technology is theoretically capable of journeys beyond Mars, humans in modern space systems will be virtual explorers interacting with the environments of distant worlds, but without the baggage of physical transportation or presence." Mark Whittington disagrees, saying Friedman is demonstrating Clarke's First Law
, and that the history of human exploration is rife with periods of stagnation interrupted by technological achievement that led to swift progress