Williams replaced the European Space Agency's German astronaut Thomas Reiter in December 2006, and is staying on board the ISS longer than the other 14th Expedition members, U.S. astronaut Michael Lopez-Alegria and Russian cosmonaut Mikhail Tyurin, who returned to Earth successfully on April 21.
The U.S. astronaut will return with the next space shuttle mission, STS-117, to be flown by space shuttle Atlantis. The launch has been postponed from an original launch date in March, due to damage to an external fuel tank following a hail storm in February 2007.
On April 10, NASA officials decided to postpone the Atlantis launch until after June 8, opting to repair the fuel tank rather than to replace it.
The mission will bring on board the ISS the third Expedition 15 crewmember, U.S. astronaut Clayton Anderson, and deliver to the space station the second starboard truss segment and its associated energy systems, including a set of solar arrays.
