Monday, July 26, 1999 Published at 10:48 GMT 11:48 UK
Moon probe threatened by eclipse
The probe is due to crash into the Moon on Saturday
Nasa's Lunar Prospector probe could be disabled just three days before the final critical phase of its mission.
The spacecraft is due to crash into the Moon on Saturday as part of an experiment that will help to establish whether there is ice on the surface.
A lunar eclipse occurs when the Earth comes between the Sun and the Moon, casting the Moon into darkness.
Lunar Prospector relies on power from solar panels to keep working, and is designed to survive for a maximum period of 47 minutes in the dark before its battery gives out.
However, during the eclipse, the probe will pass in and out of the Earth's shadow for nearly three hours. With Lunar Prospector nearing the end of its intended life, vital systems could be damaged and control of the spacecraft could be lost, say Nasa.
Lunar Prospector Mission Outreach Coordinator Lisa Chu-Theilbar is cautiously optimistic though. "Lunar Prospector has gone through a couple of eclipses similar to this one and experienced no difficulties," she said.
Project scientists estimate there could be 200 million tonnes of ice in the lunar topsoil, which could be used to support human colonies and to generate fuel for manned missions to other planets.
Nasa hopes the probe's 6,115 kph (3,800 mph) impact will throw up a cloud of water vapour visible from Earth.