WASHINGTON The world's most expensive science project the $100 billion-plus International Space Station is poised to get four more years in orbit.

According to documents obtained by the Orlando Sentinel, NASA plans to announce this week that it has White House approval to extend the station's operations by four years until 2024.

The decision follows years of pressure by top NASA officials, who consider the station a critical steppingstone to future exploration. But a four-year extension likely would cost NASA about $3 billion a year from 2021 to 2024. That's a major chunk of the agency's annual budget, which is now about $17 billion, and a longer mission could force NASA to make tough financial decisions in the future.

The administration's approval, however, doesn't guarantee that the station, which has been continuously occupied since 2000, will survive past its current end date of 2020. At some point, Congress must approve a NASA budget that includes an extension of the station's life. The plan also must get the support of whoever wins the White House in 2016 though the backing of President Barack Obama now might make it harder for the next administration to renege.

Still, the move is expected to reassure NASA's international partners, who have wondered how long the U.S. plans to commit to the station. NASA's announcement coincides with a visit to Washington this week by leaders of the world's space agencies.

"Arriving at this decision in a timely and coordinated fashion will, hopefully, prove beneficial to our international partners as they struggle with decisions on funding for their space programs," NASA Chief Charlie Bolden wrote in an email to NASA and administration officials that praised the decision.

The announcement also has the potential of sending a signal to China, NASA's latest cosmic competitor.

In 2003, China become just the third country to launch an astronaut into space, and Beijing reportedly is making plans to assemble its own space station next decade.

By keeping the space station operational, NASA can maintain its own symbol of technical advancement while limiting attempts by the Chinese to woo global partners for its own outpost.

The symbolism is especially important for NASA because of the agency's recent struggles with its human-exploration program.

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NASA gets White House backing to extend space station by 4 years