Human spaceflight has so far been, at most, a succession of
forays - That is: astronauts leave the Earth's surface, travel
to some destination, stay for a very limited time and then
return to Earth as quickly as possible. This "foray mentality"
has not brought us very far. No human has yet traveled in
interplanetary space. The long-term challenges of prolonged zero
gravity, and long-term radiation exposure in the interplanetary
environment are still not completely understood. Moreover the
foray approach imposes crippling costs on space transport since
every vehicle must both deliver people to a destination and
return them as quickly as possible. Progress toward a space-
faring society, requires a habitation paradigm. One travels to a
destination with the intent to stay for an indefinite period.
(This does not imply that the means for return are not provided,
just that the stay can be prolonged.) One's efforts are directed
toward the permanent human habitation of worlds or stations
outside the Earth. In the spa