The spacecraft will remain in the new 40-kilometer orbit for about four weeks, and will then be commanded to an even closer 25-30 kilometer (approximately 15 to 19 mile) orbital path in January 1999. These actions will officially complete the end of the very successful primary mission, which began in January 1998.

"Lunar Prospector's instruments have gathered such superior data that we have far exceeded our primary mission objectives," said Sylvia Cox, NASA's Mission Manager for Lunar Prospector. "This success raises our expectations about getting an even closer look at the lunar surface, collecting data at higher resolutions, and gaining further insights about our closest celestial neighbor."

The extended mission is expected to continue through June 1999, during which time the five instruments onboard will gather additional science data at significantly higher resolutions.

These higher resolutions will enable scientists to continue to refine their estimates concerning the concentration and form of hydrogen detected at the north and south lunar poles, which mission scientists interpret as deposits of water ice.

Mapping of the Moon's magnetic and gravity fields will also benefit greatly from the lower orbit. Additionally, initial global maps of the Moon's elements will be confirmed with the close-up data.