Three astronauts have blasted off for the International Space Station, where they are set to raise the outpost's crew to six for the first time.
Belgian Frank De Winne, Canadian Robert Thirsk and Russian Roman Romanenko launched from the Baikonur Cosmodrome, Kazakhstan at 1134 BST.
Rather than coming straight home, the current residents are to stay aboard the ISS with the new arrivals.
After four months, Mr De Winne will take over as commander of the ISS.
This will mark the first time a European has taken charge of a crew in orbit.
What we'll do over the next months will be to prepare for future space exploration
Frank De Winne, Esa astronaut
The astronauts are due to arrive at the space station in two days' time, joining the current crew - Russian cosmonaut Gennady Padalka, Nasa astronaut Michael Barratt and Japanese astronaut Koichi Wakata.
The Soyuz TMA-15 is set to dock with the space station at 1336 BST on Friday.
Mr Thirsk called the expansion from a three-person to a six-person crew a "milestone" and said one of the mission goals was "to prove the station can support six people for a long duration".
A primary objective will be to assess how well such a large number of people live together in the cramped confines of the space station.
The new astronauts will arrive at the space station on Friday
Simonetta di Pippo, director of human spaceflight at the European Space Agency (Esa), said the flight opened up "new and exciting opportunities on the utilisation of the station for scientific and research activities but also to prepare future exploration missions to more distant destinations".
Mr De Winne told the Associated Press news agency: "What we'll do over the next months will be to prepare for future space exploration."
Severe winds at the launch site have raised last-minute concerns the flight could be cancelled.
The voyage will mark the first time all five ISS partner agencies will be represented by crew members on the orbiting outpost.
Mr De Winne, an Esa astronaut, will spend six months aboard the space station, initially as a flight engineer.
After a crew rotation due in October, he will take over as commander for Expedition 21 to the space station.
This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.