There is probably no artefact in the history of space exploration more precious than the first television images of the moon captured by Neil Armstrong and his fellow astronauts as they disembarked from Apollo 11 in July 1969.

Unfortunately, the magnetic tapes of those images have gone missing.

Worse still, they appear to have been missing for at least 30 years and nobody, until now, even noticed.

The man who devised the lunar camera for the mission, a retired Westinghouse engineer called Stan Lebar, is hopeful the tapes can still be recovered somewhere from the bowels of Nasa, the US space agency, or from one of the companies to which it has, down the years, outsourced its archive storage.

But, after a year of looking, he and a small band of old-timers in the space business have turned up nothing. Their hope is to track them down before they deteriorate so far as to be unreadable, then transfer them to digital format.

"This is a once in the history of mankind kind of thing, " a markedly understated Lebar said in a phone interview. "So it's important."

The world is familiar with fuzzy, grainy footage of the lunar landscape shown on the world's television screens back in 1969, and repeated many times since. But that is not what the US astronauts shot . . . it was a low-quality reproduction achieved by pointing a television camera at the monitor beaming back the original images from the lunar mission to tracking stations in California and Australia.

The high-quality originals were preserved on telemetry tape, but were never actually broadcast.

Instead, they were sent from NASA's Goddard Space Flight Centre in Maryland to the nearby US National Records Centre. Sometime in the mid-1970s, Goddard reclaimed the tapes, part of a hoard of more than 2,600 tapes it wanted for "permanent retention". And then they vanished into the bureaucratic ether.

Some similar tapes showed up in Australia a couple of years ago, but turned out to be test-run tapes for the Apollo 9 mission. That was when Lebar and a colleague at Goddard, Dick Nefzger, decided to launch a full-scale hunt for the tapes.

First they hunted through the National Records Centre, and satisfied themselves after five months that they weren't there. Now they are going through the list of retired Nasa employees to find someone who remembers where the tapes were sent, or who can explain the bureaucratic protocols of the time so they can make an educated guess.

Last month, Lebar and his friends issued a flyer appealing for help, but they have received no responses. "It's going to take a deep search, " Lebar said.

Until now, they have kept the story out of the press because they say they do not want to embarrass Nasa.

In fact, they insist it is wrong to characterise the tapes as missing.

"They're not missing, " Lebar said.

"We just haven't found them."