NASA Is Charting America’s Return to the Moon’s Surface : Space: A robot craft would orbit the moon for two years to map it, a key step toward establishing a manned lunar outpost.

The space agency is accelerating plans to send a sophisticated robotic spacecraft to the moon for two years of reconnaissance, the most tangible evidence to date that America’s return to the moon may be for real.

The robot mission would help lay the groundwork for a permanently manned outpost on the moon, planned for some time after the turn of the century.

Scientists who have long dreamed of mapping every square foot of the moon with a lunar orbiter have been meeting at the Jet Propulsion Laboratory in Pasadena recently to firm up the mission. The National Aeronautics and Space Administration recently advanced the start-up date for the project to 1992, meaning that the actual launch could come as early as 1996.

The Soviet Union has expressed an interest in joining in the project and providing a separate lunar satellite that would be launched with the U.S. spacecraft. Although there has been much talk in recent years of a joint U.S.-Soviet program, no Soviet hardware has ever been launched as part of a U.S. mission.

Although the ambitious project is still in the planning stage, scientists who are involved have expressed confidence that it will win final approval.

It is expected to cost “in the neighborhood of $500 million to $700 million,” according to Gary Parker of JPL, development flight project manager for what will be known as the “Lunar Orbiter.”

Equipped with high-resolution cameras and possibly as many as a dozen instruments, the spacecraft will orbit the moon for two years, mapping the entire surface in unprecedented detail as the moon slowly turns and the craft orbits around it. It would measure the height of the moon’s mountains and the depth of its valleys, and provide “a complete scientific inventory of the lunar surface,” according to program scientist Bevan French of NASA headquarters.

Although scientists believe the mission is justified solely on the basis of the facts it would reveal about the history, composition and origin of the moon, the driving force behind the mission is the need to find the best candidates for a manned outpost on the moon. Such a facility is part of the long-range space-exploration program recently embraced by President Bush.

The craft is to carry instruments that will “be critical in telling us where to put the lunar outpost,” said Michael Drake of the University of Arizona, a member of NASA’s Lunar Exploration Science Working Group, which has been meeting the last few days at JPL.

John Lewis, a planetary scientist at the University of Arizona and another member of the working group, concurred.

“We could return to the moon without the Lunar Orbiter,” he said. “But I consider that . . . unwise. It would be silly to ignore what we can learn in the meantime.”

Lewis believes one of the fundamental purposes of the lunar outpost will be to use the moon’s natural resources in the exploration of space. “If you can bring a ton of equipment from the Earth, make 100 tons of products (on the moon), you have saved 99% of your launch costs,” he told a JPL symposium.

But to do that, scientists must first know which areas of the moon are most promising in terms of resource extraction. The orbiting craft will study X-rays and gamma rays reflected from the lunar surface, and that will tell scientists on Earth which minerals are contained in the soil.

“It may be there is one small area that is uniquely appropriate for producing oxygen,” he said. “We don’t know that.”

If oxygen could be produced on the moon, possibly from lunar rocks, it would be extremely important because rocket fuel consists primarily of oxygen and, to a lesser degree, hydrogen, which also should be readily available on the moon. That would open the door to fabricating propellants on the moon to send rocket ships off to explore the rest of the solar system.

Because the overwhelming majority of material fired into space from Earth consists of propellants, if rocket fuel could be derived instead from the moon it would save enormously in the cost of space exploration, scientists contend. Spacecraft could blast off from the moon, which has only one-sixth the gravity of Earth, to explore such places as Mars without the need for lifting their propellants from the surface of the Earth.

The moon is believed to be devoid of water, but some scientists speculate that some water in the form of ice may exist at the moon’s polar caps, which have never been adequately mapped. That would make the problem of generating rocket fuel far simpler, because water contains the two ingredients needed for propellants--hydrogen and oxygen.

“If it (polar ice) is there, it is the most important single resource on the surface of the moon,” Lewis said.

The feasibility of a permanent outpost on the moon would depend largely upon whether the moon’s resources can be used to help build the facility.

For example, the Earth’s atmosphere makes life here possible because it shields humans from potentially lethal bursts of solar radiation. But the moon’s atmosphere is so thin it is virtually non-existent, so it would not afford that protection.

That means the astronauts will have to have some kind of radiation shielding, and scientists foresee shelters built from materials found on the moon.

“It is unthinkable that radiation shielding would be transported from the Earth” because it would weigh too much, Lewis said.

But no one can say for sure just which lunar materials would serve that purpose the best.

“At the moment, we don’t know what 90% of the moon is made of,” said French, the program scientist.

French said NASA has had “very preliminary” talks with the Soviets, who have expressed interest in providing a “sub-satellite” that would be launched aboard the same rocket as the Lunar Observer and go into a higher orbit around the moon.

The purpose of the Soviet satellite would be to help measure the speed of the Observer as it orbits the moon. Because of variations in the moon’s gravitational field, caused by variations in lunar density, the Observer will speed up in part of its orbit and slow down in others.

If that change can be measured precisely, it would tell scientists much about the interior and composition of the moon. That is important because it could help resolve one of astronomy’s oldest mysteries: Where did the moon come from?

The prevailing theory today--which UC San Diego chemist James Arnold said merely describes the origin of the moon “less badly” than other explanations--is that the moon was once part of the Earth. According to this theory, a “Mars-sized projectile” struck the Earth more than 4 billion years ago. The cataclysmic impact sent debris flying into orbit around the planet, which eventually coalesced into the moon.

If that is the way the moon was created, scientists would like to know because it would tie the origin of the moon to the origin of the Earth.

“To understand how we came to be where we are, we need to understand the origin of the moon,” said Roger Phillips, a geologist with Southern Methodist University and chairman of the working group.

The Lunar Observer would be a major step in that direction, Phillips said, because it would provide scientists with their first comprehensive look at the total surface of the moon.