A Nasa astronaut and two Russian cosmonauts docked with the International Space Station (ISS) early on Thursday, beginning a four-month mission aboard the orbiting complex.

A Russian Soyuz TMA-04M capsule carrying NASA astronaut Joe Acaba and cosmonauts Gennady Padalka and Sergei Revin docked with the ISS at 4:36 a.m. GMT as the two spacecraft sailed 400 kilometers above the border between Mongolia and Kazakhstan, Russian Mission Control said.

“Everything went off smoothly,” Padalka told Mission Control.

The trio began their journey on Tuesday when they launched from the Baikonur Space Center in Kazakhstan, in Russia’s first manned flight for almost five months. They were originally scheduled to blast off on March 29, but the start date was postponed due to technical problems.

The new arrivals will join fellow Expedition 31 members, Commander Oleg Kononenko, NASA’s Don Pettit and Dutchman Andre Kuipers, who have been aboard the station for almost five months since arriving in December.

The hatches between the two spacraft will be opened around 08:00 GMT, when the vehicles will have undergone leak and pressure checks. The three will then enter the station itself.

The docking came as Acaba marks his 45th birthday, NASA said.

He had visited the ISS in March 2009 aboard the space shuttle Discovery, the U.S. space agency said.

For Padalka, it is his fourth long-duration spaceflight and his third aboard the outpost. Revin is travelling into space for the first time.

Their mission, expected to last for 126 days, will involve about a hundred experiments, a spacewalk and the expected arrival of the first commercial cargo craft at the ISS.