Ever since the first space shuttle flight, space enthusiasts have decried the wastefulness of discarding the huge external fuel tank that helps boost a shuttle into orbit. So when NASA put out a call for profitable uses of these tanks, many organizations let their imaginations soar. NASA had hoped for small experiments that could be tucked away in unused nooks and crannies to take advantage of the half-hour spent by each tank in low gravity before it burns up upon reentry. But the size (154 feet long and 27.5 feet in diameter) of the vessels and the minimal additional boost required to put them in low-earth orbit brought greater things to mind. More than half of the eight proposals NASA received suggested turning the tanks into orbiting space stations. Variations on this theme came not only from such prestigious outfits as the University Corporation for Atmospheric Research, but also from...