03/12/2009 Due to a leak in the venting system outside the giant external fuel tank, NASA has decided to postpone the launch of a space shuttle headed to the International Space Station (ISS), originally scheduled for 9:20 EDT on March 12. The launch has been rescheduled for Sunday, March 15 at 7:43 PM EDT. Discovery will carry a crew of seven astronauts, including Flight Engineer Koichi Wakata, KC5ZTA; Wakata is with the Japan Aerospace Exploration Agency (JAXA). He will stay on the ISS, replacing Flight Engineer Sandra Magnus, KE5FYE, who will return home on Discovery. Wakata is scheduled to return to Earth when Endeavour launches to the ISS in June 2009; Flight Engineer Timothy Kopra, KE5UDN, will replace Wakata. Discovery's 14 day mission, which has four spacewalks scheduled, will deliver the fourth and final set of solar array wings to the ISS. With the completed array, the station is expected to be able to provide enough electricity when the crew size is doubled to six in May. The shuttle also will carry a replacement for a failed unit in a system that converts urine to drinkable water.