Also watching intently will be a University of Arizona planetary scientist who is sending a memorial tribute aboard the satellite.

UA astronomers and others observing near Tucson are part of an extensive network that will be searching for water vapor in Lunar Prospecto's impact plume.

Since its launch in January 1998, Lunar Prospector has scored a number of scientific coups, as well as a followup confirmation of possible water-ice deposits at the north and south lunar poles. The question is whether the hydrogen it detected exists in water ice or in hydrogen-containing compounds called hydrates. Not all scientists agree this experiment will definitively answer the question.

However, the answer is of scientific and practical interest for future space explorers. Sending a pint of water to the moon costs $10,000. So picking it up at the south lunar pole could turn out to be one of the biggest bargains in this part of the solar system.

Aerospace engineers at the University of Texas in Austin were the first to conceive of crashing Lunar Prospector into a frigid, shadowed crater at the lunar south pole just before the satellite runs out of fuel. The 354-pound (161 kg) Lunar Prospector will be traveling at 3,600 mph (5,793 kph) or faster. If the impact plume it generates is large enough -- and that's a big "if," scientists emphasize -- observers might discover the first irrefutable proof of water on the moon. But scientists caution that it may take weeks or months of data crunching before this is confirmed.

The project was approved by officials at the NASA Ames Research Center in Moffett Field, Calif., which manages the mission, and at NASA Headquarters in Washington, D.C. Observers will watch for the impact plume with telescopes at several locations including Texas, California, and Hawaii. Those involved will include the Hubble Space Telescope, the Keck 1 telescope, and the MacDonald Observatory telescopes.

If monsoon clouds don't obscure their views. Ann L. Sprague and Stephen M. Larson, both of the UA Lunar and Planetary Laboratory (LPL), will observe with telescopes in the Santa Catalina Mountains north of Tucson. Other astronomers will use the McMath-Pierce and WIYN telescopes on Kitt Peak, southwest of Tucson.

Sprague and her colleagues will use the UA's 1.54 meter (61-inch) telescope on Mount Bigelow to monitor sodium in the moon's diaphanous atmosphere before, during and after impact. They are trying to learn more about the structures of the thin atmospheres on the moon and planet Mercury by using spectroscopy to look for sodium and other elements.

Larson will install special filters on the 1.52 -meter (60-inch) NASA reflector telescope on Mount Lemmon to look for OH, a byproduct of water. "Given the moon's low declination and the monsoon weather, I don't expect anything close to Keck or HST results, but I'll be looking anyway," he said.

The 61-inch telescope was built by the late Gerard Kuiper, who founded LPL, in the early 1960s to survey the moon in preparation for the lunar spacecraft missions being proposed at that time. Kuiper died in 1973. His ashes were placed at the 61-inch telescope during a small LPL celebration last month. The Mount Lemmon 60-inch telescope, also built by Kuiper, was used for lunar laser ranging observations after Apollo 11.

Shoemaker Tribute Aboard Lunar Prospector

The filters Larson will use are the same ones he used in photographing Comet Hale-Bopp from Tucson in April 1997. One of those images rides on a small, polycarbonate capsule that is hitching a ride to the moon aboard Lunar Prospector. The capsule is wrapped in a piece of brass foil inscribed with Larson's image of Comet Hale-Bopp, an image of Meteor Crater in northern Arizona and a passage from Shakespeare's "Romeo and Juliet."

Inside the capsule are the ashes of the late Eugene M. Shoemaker. Shoemaker was a pioneering planetary geologist famous for his work on extraterrestrial impacts and for his later collaboration with his wife, Carolyn, in the study and discovery of comets. He was killed in a July 1997 auto accident in Australia. LPL Associate Professor Carolyn C. Porco conceived, designed and produced this tribute honoring Shoemaker in time for the Lunar Prospector launch only months after Shoemaker's death.

"It was legend among planetary scientists that Gene's life-long dream was to go to the moon and study its geology firsthand," Porco said. "At his journey's end -- thirty years to the month after humans first set foot on the moon --- Eugene M. Shoemaker will become the first inhabitant of Earth to be sent to rest on another celestial body," Porco said.

Porco has produced replicas of the Shoemaker tribute foil for museum display. They have been sent to the Smithsonian Air and Space Museum in Washington, D.C.; the Adler Planetarium in Chicago, the Hayden Planetarium in New York and the U.S. Geological Survey headquarters in Reston, Va.,

Copies also have been given to the U.S. Geological Survey Gene Shoemaker Building, which is under construction in Flagstaff, Ariz.; the Meteor Crater Visitor Center; NASA Ames Research Center; NASA Headquarters; and the UA Lunar and Planetary Laboratory. Additional copies have gone to Carolyn Shoemaker; NASA Chief Administrator Dan Goldin; Wesley Huntress, formerly head of the NASA Space Sciences Division; and Bruce Babbitt, U.S. Secretary of the Interior.