Discovery launch; No earlier than Sunday

CAPE CANAVERAL, Fla., March 12 (UPI) -- The U.S. space agency says space shuttle Discovery's launch to the International Space Station is tentatively targeted for Sunday evening.

National Aeronautics and Space Administration officials postponed Wednesday's planned liftoff due to a leak in a hydrogen venting system outside the rocket's external fuel tank. The system is used to carry excess hydrogen safely away from the launch pad.

Sunday's launch would be at 7:43 p.m. EDT but NASA said the exact launch date is dependent on the work necessary to repair the problem.

Discovery's 14-day STS-119 flight will deliver the space station's fourth and final set of solar array wings that provide electricity to power science experiments and will support the station's expansion to six crew members in May. STS-19 will also include replacement of a failed unit that converts urine to potable water. Four spacewalks are planned, NASA said.