Space.com: Whereas the Cold War motivated the US to put a man on the Moon, it has been more than four decades since any other similar manned missions have been undertaken. While the US has been considering missions to other destinations, including Mars and an asteroid, countries such as China, India, Iran, Japan, and Russia have been revisiting the idea of exploring the Moon. Now some scientists in the US are also pushing for the Moon because of its proximity to Earth. At just three days’ travel, they say, the Moon is the most viable location for a semipermanent research base and space colonization efforts, since it would be much easier to restock supplies and mount potential rescue operations. In addition, because of the rising costs involved, future missions will probably require international cooperation, and the Moon offers the best prospects for that.