Having spent 18 months probing the moon's surface and interior, Lunar Prospector is running out of fuel, and is expected to crash at the end of July. Rather than just let it go, however, NASA decided to give the satellite a final mission: to take aim at a crater near the moon's south pole and slam into it at 3,600 M.P.H.
Why would NASA do that? In a word, water. With water, the moon can be used as a way station for human space exploration. Without it, H2O has to be hauled into space at a cost of more than $10,000 per lb.
The idea is to crash Prospector into what NASA scientists think might be a huge ice field and hope the impact sends up an icy spray big enough to be spotted--and measured--by the Hubble and ground-based telescopes. Controllers need to fly it into the right crater at just the right angle, and smack bang into the middle of the ice field. Says University of Texas aerospace engineer David Goldstein, who proposed the suicide splashdown: "It's going to be a close call."
--By Dick Thompson/Washington