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.

Water on the Moon would be useful to future Lunar missions

But space agency officials warned on Monday that a partial lunar eclipse on Wednesday may disable the spacecraft's components.

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.

Cautiously optimistic

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.

A lunar eclipse throws a shadow across the Moon

Since its launch in January 1998, Lunar Prospector has provided the most detailed geological maps ever of the Moon's surface. It has also detected Hydrogen - which could signal the presence of ice in the bottom of craters where the Sun's rays never reach.

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.