An American astronaut and two Russian cosmonauts arrived at the International Space Station early Thursday, kicking off a four-month stay aboard the orbiting laboratory.

A Russian Soyuz spacecraft carrying NASA astronaut Joe Acaba and cosmonauts Gennady Padalka and Sergei Revin docked with the space station at 12:36 a.m. ET Thursday as the two spacecraft soared 249 miles above the border between Mongolia and Kazakhstan.

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"Everything went very smoothly, very well," Padalka radioed the Russian Federal Space Agency's Mission Control Center in Moscow just after docking.

For Acaba, the docking came as a welcome birthday present to mark his 45th birthday, NASA commentator Rob Navias said.

The three spacefliers were due to float into the orbiting lab's hatch overnight, bringing the station back up to its full crew of six. Their fellow Expedition 31 crew members NASA's Don Pettit, Dutch astronaut Andre Kuipers and Russian cosmonaut Oleg Kononenko have had the $100 billion orbiting complex to themselves since April 27.

Acaba, Padalka and Revin launched Monday from the Baikonur Cosmodrome in Kazakhstan. They were originally scheduled to blast off on March 29, but a botched pressure test cracked their Soyuz capsule, causing a six-week delay while another spacecraft was readied. [See Spectacular Soyuz Launch Photos]

A four-month space stay The three new arrivals will live and work aboard the space station for four months, returning to Earth in mid-September. All will serve as flight engineers under Kononenko, the commander of the Expedition 31 mission.

Kononenko, Pettit and Kuipers boarded the orbiting lab in late December and are scheduled to depart on July 1.

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US-Russian crew arrives at space station