NASA and its international partners have assigned three new International Space Station crew members.

HOUSTON, Sept. 2 /PRNewswire-USNewswire/ -- NASA and its international partners have assigned three new International Space Station crew members.

Expedition 21 Flight Engineer and Soyuz Commander Roman Romanenko, European Space Agency Flight Engineer Frank De Winne and Canadian Space Agency Flight Engineer Robert Thirsk have returned to Earth, landing on the steppes of Kazakhstan in their Soyuz TMA-15 spacecraft.

NASA astronaut and US Army Col Tim Kopra has become the first International Space Station crew member to use the social media tool Twitter to discuss living and working in orbit.

Since the arrival of three new astronauts to the International Space Station on May 29, the orbiting outpost has become home to six crewmembers for the first time in its history.