I am coming to the conclusion that robots like Spirit and Opportunity can produce much more Science than humans for the same price. The cost of human exploration is enormous. Humans need food, oxygen, water and produce wastes. They need a very narrow temperature range to survive.

The two robots on Mars now are the harbingers of a robot exploration corps. Eventually, we can send further missions with extensive automatic laboratories to analyze samples. Such laboratories can be miniaturized; humans can not. Such laboratories will be able to cut samples into thin slices and examine them with microscopes, both optical and electronic.

I expect to see robots with ranges measured in thousands of kilometer exploring Mars in a decade or two. Powered by photovoltaic arrays, these roving robotic explorers will be equipped with drills capable of recovering core samples from hundreds or even thousands of meters in depth. They will roam all over Mars finding samples and returning these samples to laboratories which will either be stationary or even built-in. These robots will operate for years, returning fresh data on a daily basis.

While the development of fully automatic deep drilling equipment with the requisite robustness and reliability will be costly, it will cost less than the development of any realistic manned mission. In particular, there will be no need for fuel or supplies for the return trip since there will be no return trip.

Even so, with all of this equipment, a extensive robotic exploration mission will require far less boosted mass and will cost far less than any practical manned mission.

At least, that is how I see it.