On May 27, 2009, three astronauts launched to the International Space Station to complete the crew of Expedition 20. [‘On This Day in Space’ Video Series on Space.com]

Expedition 20 was the first six-person crew to live and work at the space station for a long-duration stay. Russian cosmonaut Roman Romanenko, Canadian astronaut Robert Thirsk and Belgian astronaut Frank De Winne lifted off on a Soyuz rocket from the Baikonur Cosmodrome in Kazakhstan. Two days later, they arrived at the space station, where they were greeted by the Russian commander Gennady Padalka, NASA astronaut Michael Barratt and Japanese astronaut Koichi Wakata. For the first time in ISS history, the space station was packed to its full capacity of six crewmembers. Previous Expedition crews consisted of three people. But ever since Expedition 20, the space station has continued to support crews of six. Because the Soyuz capsules that ferry people to and from the ISS can only fit three people, only half of each Expedition crew can launch at a time. This is why it too two launches to get the full crew of Expedition 20 to the space station.