Thomas Reiter 's position was previously planned to be filled by Sergey Volkov ( Russia ) before the launch of STS-121 was postponed until July 2006 . Previously , the position of Thomas Thomas Reiter was planned to be filled by Sergey Volkov ( Russia ) before the launch of STS-121 was postponed until July 2006 . Previously , it was planned that Sergey Sergey Volkov 's position would be filled by Thomas Reiter ( Russia ) before the launch of STS-121 was postponed until July 2006 .