The basic advantage of astronauts is that they can explore Mars in real time, free of communications delays and capable of following up interesting results with new experiments. Robots, even after decades of research to make them completely autonomous, cannot manage without people in the loop. But the question arises: Where should the astronauts be? The obvious answer–on the surface of Mars–is not necessarily the most efficient. At the first “Case for Mars” conference in 1981, one of the more provocative conclusions was that the Martian moons, Phobos and Deimos, could serve as comparatively inexpensive beachheads.