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updated 9/15/2011 9:17:40 PM ET 2011-09-16T01:17:40

This story was updated at 8:45 p.m. EDT.

An American astronaut and two Russian cosmonauts are headed back to Earth tonight after wrapping up a months-long stay aboard the International Space Station.

The Soyuz TMA-21 spacecraft ferrying the spaceflyers home is due to land at 12 a.m. EDT (0400 GMT) on Friday (Sept. 16) on the steppes of Kazakhstan in Central Asia, where the local time will be about mid-morning.

Returning home on the Soyuz spacecraft are NASA astronaut Ron Garan and cosmonauts Andrey Borisenko and Alexander Samokutyaev. The three men have been living in space for 164 days, and they formed half of the space station's six-man crew.

Garan has been posting updates and photos of his mission every day using the social networking site Twitter. Even on his last day in space, he managed to send his 86,000 followers a message.

"Thanks 4 being w/me on this amazing journey," Garan wrote. [ Amazing Photos by Astronaut Ron Garan ]

Garan and his crewmates bid farewell to the rest of the space station's crew today at 5:30 p.m. EDT (2130 GMT), when they closed the hatches between the orbiting lab and their Soyuz space capsule.

The Soyuz spacecraft undocked from the station at 8:38 p.m. EDT (0038 GMT); it's slated to fire its engine about 2 1/2 hours later to begin the descent through Earth's atmosphere.

"Safe journey and soft landing, my friends," NASA astronaut Mike Fossum, who's staying behind on the orbiting lab, said as the Soyuz drifted off into space. "Godspeed from the International Space Station."

Garan, Borisenko and Samokutyaev made up part of the Expedition 28 crew of the International Space Station, with Borisenko commanding the mission. On Wednesday, Borisenko turned control of the space station over to Fossum, who now leads the outpost's Expedition 29 mission.

Russian cosmonaut Sergei Volkov and Japanese astronaut Satoshi Furukawa also remain aboard the station. The three men will remain in space for the next three months.

Meanwhile, another three-man crew is preparing to launch toward the space station.

A Soyuz 28 spacecraft carrying NASA astronaut Daniel Burbank and cosmonauts Anatoly Ivanishin and Anton Shkaplerov is set to launch from Kazakhtan's Baikonur Cosmodrome on Nov. 14 and arrive at the space station two days later.

The Soyuz 28 spaceflight was delayed from a late September liftoff following the failed launch of a Russian Soyuz rocket carrying an unmanned space station cargo ship last month.  A malfunction in the gas generator in the Soyuz rocket's third stage engine caused the failure. The Soyuz and its cargo ship, called Progress 44, ultimately crashed in Siberia.

Since the Progress 44 cargo ship launched on a Soyuz rocket similar to that which will carry the Soyuz 28 crew, NASA and Russia's Federal Space Agency agreed to ground all station-bound flights until the cause could be determined.

You can follow SPACE.com Managing Editor Tariq Malik on Twitter @tariqjmalik. Follow SPACE.com for the latest in space science and exploration news on Twitter @Spacedotcom and on Facebook.

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