This is from the report I linked to in the post below:

Two particular destinations in near-Earth space could serve as useful and interesting first steps toward exploring deep space. The closest is the Moon, which many consider to be the best first destination for a human space exploration enterprise eventually leading to Mars. Numerous in situ scientific investigations remain to be performed on the Moon in order to add to our understanding of the origin and evolution of the Earth, and many have argued that these investigations warrant the presence of human intelligence. Although the Moon lacks an tmosphere and has only half the surface gravitational acceleration of Mars, it may nonetheless offer numerous advantages as a “testing ground” for human missions to Mars, lessening the steepness of the learning curve for future Mars expeditions.

Scientific interest in returning to the Moon remains high, and the Moon has potential utility as a stepping-stone for the exploration of Mars. In addition, there will be great interest in the Moon among spacefaring nations that have not yet sent humans there—both for national prestige and as a confidence-building step before participating in an international Mars expedition. Europe presently has a lunar robotic mission, and Japan, China, and India are all developing their own such missions. The Moon remains a valid destination in its own right, and any transportation architecture should be designed with this in mind.