Three International Space Station crew members landed safely back on Earth Sunday, culminating a 6 1/2-month mission, NASA staff said. Staff at the Johnson Space Center in Houston said the trio of space travelers who comprised the crew of Expedition 31 -- Russian Commander Oleg Kononenko, NASA flight engineer Don Pettit and European Space Agency flight engineer Andre Kuipers -- landed their Soyuz TMA-03M spacecraft in Kazakhstan at 2:14 p.m. local time (3:14 p.m. EDT). They had left the space station\'s Rassvet module Saturday night. The three crew members had arrived at the station Dec. 23 and spent a total of 193 days in space, with all but two of them aboard the space station. Their work while at the station helped support more than 200 scientific investigations involving more than 400 researchers worldwide. The studies ranged from integrated investigations of the human cardiovascular and immune systems to fluid, flame and robotic research, NASA said. Before heading back to Earth, Kononenko handed over command of Expedition 32 to Russia\'s Gennady Padalka, who remains at the station with NASA astronaut Joe Acaba and Russian cosmonaut Sergei Revin. NASA astronaut Sunita Williams, Russian cosmonaut Yuri Malenchenko and Japan Aerospace Exploration Agency astronaut Akihiko Hoshide will join them July 17. Williams, Malenchenko and Hoshide are scheduled to launch July 14 from the Baikonur Cosmodrome in Kazakhstan.