MOSCOW (Reuters) -- Russia's Mir space station, which has circled the earth empty since August, may be sent another crew this year for an extended flight, paid for by a U.S. firm, Mir's builders said on Monday.

Mir has been empty and partly shut down since August and is to be crashed into the Pacific Ocean unless Russian officials can find funds to keep it aloft.

Sergei Gromov, spokesman for Russia's Energiya rocket builder, told Reuters by telephone that a U.S. firm, Golden Apple, had promised to send $20 million by March to continue the program.

Gromov said the builders planned to send a crew to Mir in March for a mission lasting at least 45 days. He said the U.S. firm had already paid $7 million of the $20 million promised, but gave no further details about the company.

If the Mir program were to be ended, a crew would probably fly to the station for a brief mission to shut it down before it was guided on a crash course into the Pacific.

The Mir program has given Russia by far the world's most extensive experience of long-term piloted space flight, and the country is using that knowledge to build the main living quarters of the new $60 billion International Space Station.

But the new station has been repeatedly delayed and the United States wants Russia to abandon Mir and focus its resources on the new orbiter.

Mir has stayed in orbit long past its original five-year life span and was plagued by problems in the late 1990s. Russian space officials have been reluctant to abandon the prize achievement of their space program.

Over the past year, various schemes have been floated to find commercial funding or private donors to save Mir.

Last year a British entrepreneur, Peter Llewellyn, promised $100 million to save Mir if he were allowed to ride on it, but he never paid up and was sent home before completing a training course at Russia's Star City space base.