A joint collaboration between India's Chandrayaan-1 and National Aeronautics and Space Administration's Lunar Reconnaissance Orbiter, which are orbiting the moon, could turn up evidence for valuable lunar water. 

Some scientists suspect water ice, which would be a precious resource for future explorers, may be trapped in permanently shadowed craters at the moon's poles.

Water ice can be distinguished from other materials by the way its radar echoes vary according to the position of the listener. 

In 1994, the United States' Clementine spacecraft bounced radar signals off the moon and found hints of the water-ice signature.

But it listened for the reflections jointly with a radio observatory on Earth, and getting unambiguous evidence for water requires more closely spaced listening posts. 

According to a report in New Scientist, a recent joint experiment involving the US and Indian space agencies has provided an unique opportunity to get that data.

"It's a unique experiment that can only be conducted by two spacecraft in orbit at the same time," said Jason Crusan from the NASA headquarters in Washington, DC.

On August 20, NASA's Lunar Reconnaissance Orbiter and Chandrayaan-1 were manoeuvred to within a few dozen kilometres of each other, which required close communication and coordination between NASA and the Indian Space Research Organisation.

Once in proper formation, Chandrayaan-1 fired its radar beam at a crater near the moon's north pole, while both spacecraft listened for the echoes. 

Crusan said that scientists were still analysing the data to make sure the experiment worked, but added that both spacecraft were in the right positions at the right time for it to go as planned.

This is probably the only time the two spacecraft will perform this kind of joint radar measurement, since LRO will soon move to a lower orbit than Chandrayaan-1, in order to begin its main observing phase.

But last week's experiment marks a new level of space cooperation between the US and India.

"I hope this is a sign of the future for how we will do cooperative exploration," Crusan said. "I think it's a good first step," he added. 

An Image of the Leibniz crater taken by Chandrayaan-1