LUNAR PROSPECTOR UNVEILED : 8-FOOT-TALL, LOW-COST PROBE SET FOR SEPTEMBER RENDEZVOUS.

Byline: Catalina Ortiz Associated Press 

NASA is shooting for the moon again.

The space agency last week showed off its Lunar Prospector, a new, low-cost probe that will give the United States a close look at the moon for the first time in a quarter century.

The unmanned craft, to be launched in September, will orbit the moon for at least a year, map the composition of the moon's surface, measure its magnetic and gravity fields and look for signs of volcanic activity.

It also will look for evidence of ice, which scientists believe may lie in polar craters never touched by the sun.

Scientists hope the probe will yield important data about the moon, which in many ways remains mysterious despite earlier probes and the Apollo landings.

``Many people are under the impression we've been there and done that. That's not true,'' said G. Scott Hubbard, head of the NASA mission.

The $63 million Lunar Prospector was recently completed at Lockheed Martin Missiles and Space in Mountain View, about 40 miles south of San Francisco. The project is being supervised by NASA at the nearby NASA-Ames Research Center.

NASA escorted reporters into a ``clean room'' at Lockheed Martin to show them the spacecraft, which is 8 feet tall, including its antenna, 4 feet wide and 660 pounds in weight.

It will take five days to reach the moon after its launch from Florida on Sept. 24 and will circle its poles at what is considered a close distance of 62 miles. After a year, it is likely to orbit at an altitude of only 6.2 miles before eventually crashing on the surface.

The last time NASA got that close was in December 1972 with the last moon landing, the Apollo 17 mission. Since then, only a few spacecraft have approached the moon, most simply flying by.

Clementine, a military test satellite, did orbit the moon in 1994. It came no closer than 250 miles of the surface, but it intrigued scientists when radio signals it bounced off the moon suggested the presence of ice.

Some of the equipment on the Lunar Prospector will look for hydrogen, an almost certain sign that water is on the moon, brought there by comets. Scientists said the presence of water - specifically its elements hydrogen and oxygen - could someday enable astronauts to make fuel for return trips from the moon for missions to Mars and other planets.

Alan Binder, a Lockheed Martin scientist and head investigator of the project, said the Apollo missions provided most of what we know about the moon. Still, he pointed out, astronauts had only a total of three days to gather data in limited areas. Only a quarter of the moon's surface has been mapped in detail.

``The surface area of the moon is equal to that of North and South America combined. So imagine how little we would know of our continent if we had six survey crews walking around for three days in this area,'' Binder said.

NASA considers the Lunar Prospector a bargain at $63 million, far lower than most scientific crafts.

Hubbard pointed out that the first successful moon orbiter, launched in 1966, cost $260 million in today's dollars.

``We have been asked to collect much more science at one-fourth the total cost,'' he said. ``When you consider the rapid development (and) extraordinarily low cost, the Lunar Prospector may well be the most cost-effective planetary mission NASA has ever flown.''

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Photo: Alan Binder, left, principal investigator for Lockheed Martin, shows off NASA's Lunar Prospector spacecraft to the media.

Associated Press