U.S. officials are unable to communicate with an expensive experimental U.S. spy satellite launched last year by the U.S. National Reconnaissance Office (NRO), a defense official and another source familiar with the matter said on Thursday.

Efforts are continuing to reestablish communication with the classified satellite, which cost hundreds of millions of dollars, but "the prognosis is not great at this point," said the defense official, who asked not to be identified.

A Delta II rocket for United Launch Alliance lifts off at Vandenberg Air Force Base, Callifornia, December 14, 2006. [Reuters]

"They have not yet declared it a total loss. There are still some additional steps that can be taken to restore communication," the official added, noting some satellites had been recovered in similar situations in the past.

The official said the problems were substantial and involved multiple systems, adding that U.S. officials were working to reestablish contact with the satellite because of the importance of the new technology it was meant to test and demonstrate.

The other source said the satellite had been described to him as "a comprehensive failure."

There was no suggestion by either of the sources that the satellite had been purposely damaged as part of a terrorist attack. Another government official said he had no information about any attacks on U.S. satellites.

The National Reconnaissance Office, which designs, builds and operates reconnaissance satellites for the U.S. military and intelligence communities, had no comment.

Jonathan McDowell, an astronomer with the Harvard- Smithsonian Center For Astrophysics, said the satellite in question could be a classified NRO satellite launched into space on December 14 from Vandenberg Air Force Base in California, which did not appear to be part of any "existing pattern."

The NRO satellite identified only as L-21 was the first ever launched by the newly merged rocket launch units of Boeing Co. and Lockheed Martin Corp..

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