But visions of thriving lunar villages serving as the staging points for manned voyages to Mars and beyond ignore the incredible difficulties of lunar mining and space travel.
Yes, a moon with water could conceivably support a human population. In theory, there are two possibilities:
A colony at a pole, adjacent to the deep craters with permanently shadowed bottoms that apparently keep water - released by collisions with comets and asteroids - in cold storage.
These regions also have mountains. If the peaks are high enough to be perpetually illuminated - the sun circling over the horizon half-set but never disappearing - they would be viable for solar-powered bases.
But the poles would be far less accessible by spacecraft than the moon's equatorial regions, requiring far more fuel to reach.
More feasible might be establishing a colony at the more hospitable equatorial regions and using rockets to ship the ice in from the poles. But this would be remarkably inefficient, requiring four engine firings for each trip: takeoff from the pole, Apollo-style landing at the equator, takeoff of the empty rocket on the return trip and another landing at the pole.
The whole time, the rockets would be fighting the moon's gravity, which is far less than Earth's but still a drain on fuel.
Or the ice could be shipped 2,000 miles by lunar vehicle, a trip that would take about two months at around 4 mph.
In any case, as a refueling station, the moon is relatively out of the way for trips to other planets. Its gravitational field would require spaceships to waste valuable fuel for takeoffs.
A spaceport in low Earth orbit that would resupply spacecraft just after they had spent most of their fuel escaping the strongest part of Earth's gravity might make more sense.
If we are intent on finding a fuel supply in space, hundreds of sources of water are more convenient. About half the asteroids that cross Earth's orbit of the sun appear to be extinct comet cores, huge dirty snowballs with thin surface layers of dust. At least a quarter of these dead comets are easier to reach than the moon, and it would require much less fuel for ships to return from asteroids than to escape the moon's gravity.
Clementine's findings were a tremendous coup for the space program, and one of its greatest successes was in showing us that space can be explored much more quickly, and with smaller and cheaper spacecraft, than seemed possible a decade ago.
The launch of the Mars Pathfinder mission is another example of good space science with an eye on cost and practicality.
Let's continue on that path, realizing visions of lunar filling stations may be premature.
John S. Lewis, co-director of the University of Arizona's Space Engineering Research Center, is author of ``Mining the Sky'' (Addison Wesley Longman Inc., 1996). This column originally appeared in the New York Times.
