Jul 29, 1999

A Stay of Execution for Lunar Prospector



A stay of execution for Lunar Prospector


Lunar Prospector survived the July 28 partial lunar eclipse in good condition for its scheduled crash landing on July 31, 1999




July 28, 1999 lunar eclipse.  Image credit: Ziggurat Creative & Technical Publishing
July 29, 1999: Mission controllers at NASA/Ames report that the Lunar Prospector spacecraft has survived the July 28, 1999 partial lunar eclipse.

Right: The July 28, 1999 eclipse as viewed from eastern Australia. The images were recorded by Marion Anderson (Department of Earth Sciences, Monash University) using a Sony Mavica FD-71 digital camera at 10x zoom plus 2x telephoto lens. Copyright: [Ziggurat Creative &Technical Publishing ]

The eclipse posed a threat to Lunar Prospector because the spacecraft's battery was designed to handle maximum shadow periods of 47 minutes before being recharged by solar arrays. During this morning's eclipse, Prospector passed in and out of regions of partial and total Earth/moon shadows for nearly 3 continuous hours. The batteries were drained and heaters required to keep important components warm were without power.


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By 2:20 p.m. PDT on July 28, 1999, the batteries were recharged and Lunar Prospector was reported to be operating normally. The spacecraft's impact into a lunar crater in search of water is expected to take place as planned at 2:51 a.m. PDT on July 31.

Scientists hope that the estimated 3,800 mph impact will exhume water vapor and rocky debris that may be detectable for several hours, although data analysis could take days or even weeks if the signal is faint. Coordinated observing teams will use NASA's Hubble Space Telescope and Submillimeter Wave Astronomy Satellite, complemented by ground-based instruments, including the McDonald Observatory in Texas and the Keck telescope in Hawaii, to seek signs of the water vapor or its byproducts.

While the probability of successful detection is estimated to be less than 10 percent, it will be a fittingly creative finish to a low-cost Discovery Program mission that has exceeded all expectations after more than 6,800 lunar orbits in 18 months.

"Regardless of the outcome of this final bold experiment, Lunar Prospector has yielded a gold mine of science data," said Dr. Henry McDonald, director of NASA's Ames Research Center, Moffett Field, CA, which has managed the mission. "We now have invaluable global maps of the moon's gravitational and magnetic fields, and the distribution of its key elements, giving us a much better understanding of the origin, evolution and composition of our rocky neighbor."


Image credit: Institute for Advanced Technology of The University of
Texas at Austin.

Above: A group of undergraduate students working within the Impact Physics Group, headed by Dr. Stephan Bless, at the Institute for Advanced Technology of The University of Texas at Austin has undertaken the ambitious project of predicting the "splash" that will be made by the impact of the Lunar Prospector on the lunar surface. Cylinders with the approximate shape and density as the satellite body are fired into a simulated "lunar soil" target at the expected impact angle (about 6.5 degrees). The impact and the resultant debris plume are photographed with a high speed camera. acquired during a shot of a plastic projectile into sand at 1.7km/s. The debris plumes (projectile remains) may be clearly distinguished from the sand kicked up. Preliminary estimates of the sand velocity indicate that some material will likely have sufficient vertical speed to rise perhaps 30km above the rim of the crater. [more information]

Launched on Jan. 6, 1998, from Cape Canaveral Air Station, FL, aboard an Athena 2 rocket, Lunar Prospector reached the moon in four days. Shortly after entering orbit over the lunar poles, its five science instruments began expanding the limited equatorial measurements made by the Apollo command modules into global, high-resolution data sets.

Lunar Prospector's data gathering has resulted in a series of discoveries and new scientific tools, including:

  • Tentative evidence that water ice exists in shadowed craters near the moon's south and north poles,
  • The first precise gravity map of the entire lunar surface,
  • Confirmation of the presence of local magnetic fields that create the two smallest magnetospheres in the Solar System, and
  • The first global maps of the moon's elemental composition.

In exceeding its design life, the $63 million Prospector mission has exhausted the bulk of its fuel and battery power. Although the drum-shaped probe will have a mass of only 354 pounds (161 kilograms) at the end, its impact energy will be equivalent to crashing a two-ton car at more than 1,100 miles per hour.

Please visit the Lunar Prospector project web site from NASA/Ames and the Lunar Prospector impact page from UT Austin for more information about the Lunar Prospector mission and its impending crash into the Moon. See also: for science news, images and impact observing hints for amateurs.

Lunar Prospector was the first of NASA's competitively selected "faster, better, cheaper" Discovery-class missions. The $63 million mission is managed by NASA Ames Research Center, Moffett Field, CA.


Web Links


Lunar Prospector in Eclipse -- The July 28, 1999 partial lunar eclipse poses a last-minute threat to Lunar Prospector. , July 28, 1999, NASA Science News


Bracing for Impact -- Astronomers prepare to observe the crash of Lunar Prospector on July 31, 1999. Includes observing hints for amateurs, July 21, 1999, NASA Science News

Destined for a Watery Grave -- NASA scientists have decided to send Lunar Prospector crashing into the Moon's south pole in search of water, June 4, 1999, NASA Science News

Zeroing in on Lunar Ice -- Astronomers explore the Lunar Prospector crash site using radar, June 4, 1999, NASA Space Science News

Lunar Prospector set to make science "splash" -- NASA/Ames press release

NASA Press Release (3 September 1998) -- announcing enhanced estimate of quantity of water on the Moon

NASA Press Release (5 March 1998) -- announcing the detection of ice on the Moon

Lunar Prospector Home Page -- from NASA/Ames

Ice on the Moon -- informative article about lunar water -- where it is and how to find it.

Lunar Prospects -- Astronomy Picture of the Day, Sep. 18, 1998

Impact Moon -- Astronomy Picture of the Day, Mar. 26, 1999

The Nine Planets: the Moon -- from SEDS

More NASA Science News


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For more information, please contact:
Dr. John M. Horack , Director of Science Communications
Author: Dr. Tony Phillips
Curator: Bryan Walls
NASA Official: M. Frank Rose