China's progress toward its own space station took a giant leap forward Friday when its Shenzhou 9 spacecraft returned to Earth with three astronauts safely aboard, Reuters reports.

China's fourth manned space mission proved an important milestone--it was the longest and most demanding yet, and included the country's first female astronaut, 33-year-old Liu Yang.

During their 13 days in orbit, Yang and two other astronauts also completed the country's transfer of astronauts between orbiting spacecraft, an important step toward its goal of manning its own space station by 2020.

If successful, China will be the only country in low orbit at the start of the next decade--the International Space Station is scheduled to go out of service in 2020. Earlier this year, the United States ended its manned space flight program.

[Photos:Space Shuttle Discovery Makes Final Flight]

The Shenzhou 9 landed with a thud in the desert of northwestern China shortly after 10 a.m. Friday. The three astronauts, unable to walk, were carried to folding chairs nearby to address the state media.

"We are proud of the motherland," said Yang, the youngest of the three astronauts. "Tiangong 1, our home in space, was comfortable and pleasant."

The Tiangong 1 ("The Heavenly Palace" in Chinese) will be retired in a few years and replaced with a space station, which China alone will operate. The country was not allowed to participate in the 16-nation International Space Station, in part because the United States feared the country would acquire advanced technology, CBS News reported.

China is just the third nation to send an astronaut to space, after Russia and the United States. The U.S. will not begin testing for a manned space mission until a 2017, and Russia has announced manned missions are no longer a priority.

Seth Cline is a reporter with U.S. News and World Report. Contact him at scline@usnews.com or follow him on Twitter.

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China's Fourth Manned Mission Brings Own Space Station Closer