This undated handout photo provided by NASA shows a six-inch lunar sample disk containing three rock pieces and three clumps of lunar dirt, similar to the one shown here, went missing after it was loaned to a Delaware observatory in 1978. (NASA/Associated Press)

Astronauts may have had the 'right stuff' to go to the moon, but when it comes to keeping track of what they brought back, NASA seems to have misplaced some of the stuff.

In a report issued by the agency's inspector general on Thursday, NASA concedes that more than 500 pieces of moon rocks, meteorites, comet chunks and other space material were stolen or have been missing since 1970. That includes 218 moon samples that were stolen and later returned and about two dozen moon rocks and chunks of lunar soil that were reported lost last year.

NASA, which has lent more than 26,000 samples, needs to keep better track of what is sent to researchers and museums, the report said. The lack of sufficient controls "increases the risk that these unique resources may be lost," the report concluded.

After last year's case of a missing moon sample loaned to a Delaware astronomical observatory, which the astronomers there claimed they returned to NASA, the agency's inspector general decided to audit about one quarter of the thousands of samples of moon rocks, lunar dust, meteorites, and other space material that the agency loaned.

Of those cases, 19 per cent of the researchers either could not account for the samples or they had material that NASA records indicated had been destroyed or loaned to someone else. That included 22 meteorites and two comet samples from a daring mission that grabbed comet chunks.

In two cases, one researcher still had nine lunar samples he borrowed 35 years ago and another had 10 chunks of meteorites he kept for 14 years. Neither had ever worked on them. Another researcher had 36 moon samples and kept them for 16 years after he had finished his research.

The audit also unearthed records that listed hundreds of samples that no longer existed.

In the Delaware case, NASA lent the Mount Cuba observatory a disk of moon rocks and moon dust in 1978 with the loan expiring in 2008.

In 2010, NASA contacted the observatory and learned that its manager had died and the observatory couldn't find the sample, the inspector general's report said.

But that is not how the observatory sees it.

"We didn't lose it," said University of Delaware physics professor Harry Shipman, a trustee of the observatory. Yes, the observatory manager died, but sometime in the 1990s "he returned it to NASA. We don't know what NASA did with it," he said.

NASA told the auditors that the observatory returned meteorites, but not the lunar sample and that still is missing, said inspector general spokeswoman Renee Juhans.

NASA spokesman Michael Cabbage said the agency will continue to lend out material to scientists and for educational display but will adopt the specific recommendations the inspector general made to improve its tracking.

"NASA does not consider these national treasure assets to be at high risk," he said.