Searching for stocks of water on the moon, Nasa crashed two spacecraft into an eternally dark lunar crater on Friday, hoping to splash ice into the light where instruments could assess it.

A two-tonne empty rocket stage hit the dark Cabeus crater near the moon's south pole at about 4:31 am PDT (1131 GMT) and a second craft crashed four minutes later.

A camera on the following spacecraft did not capture an image of the impact as hoped, but scientists said they were confident that the explosive hit took place as planned.

"We didn't see a big splashy plume like we wanted to see," said Michael Bicay, director of science at the National Aeronautics and Space Administration's Ames Research Center.

Bicay said an infrared camera showed changes that suggested an explosion.

Other instruments on the second craft, a lunar orbiter and telescopes on earth captured data that could show in days whether there was ice on the moon, and the explosion of the second craft was caught by the orbiting and earth-based observers, he and other scientists said.

Three studies released last month found clear evidence of water on the moon, welcome and surprising news for further space exploration, since water can be turned into fuel.

But the skein of water bound with dust that was disclosed then was extremely thin. "It's not enough to be of any economic importance," said Nasa Lunar Science Institute Director David Morrison.
   

Hidden in the crater near the pole, out of sunlight, could be concentrations of 2 percent to 3 percent ice in the lunar soil that would be usable. "You're going into a place where the sun hasn't shined for a billion years," Morrison said.

Hundreds of space enthusiasts in parkas and sleeping bags gathered in the early morning to watch the impact on a big outdoor screen at the Ames Research Center, housed on an old dirigible field in Silicon Valley.   

Video from the trailing spacecraft gave the sense of a silent crash fast approaching as craters edged with light grew on the screen. When the signal abruptly stopped, the sign the trailing spacecraft had also hit the surface, cheers erupted.

Nasa scientists were to give their first interpretation of data at a news conference later on Friday. -Reuters