<p>Mission managers met yesterday afternoon and into the evening to discuss an electrical problem that forced the latest postponement. They concluded the circuit breaker trouble no longer exists and the shuttle is safe to fly. But forecasters warned there is an 80 per cent chance that thunderstorms will keep Discovery on the pad. Liftoff is scheduled for 3:29 p.m. (1929 GMT).<br /><br />The decision came as dark storm clouds rolled over the launch site in Florida, putting some launch preparations on hold. Managers will reconvene before daybreak to assess the weather, before loading the shuttle's fuel tank.<br /><br />"If the forecast tomorrow morning is still as bad as it is today, there's a chance" that today's launch attempt will be called off, mission management team chairman Mike Moses said last night. "It's too early to make that call right now."<br /><br />Discovery's flight to the International Space Station was first stalled by gas leaks last week. Then a problem cropped up Tuesday with a computerized controller for one of the main engines. At this point, the mission is running three days late.<br /><br />The space agency has until Sunday to launch Discovery. Otherwise, it will have to wait until December because of sun angles. Engineers traced the electrical trouble to a circuit breaker that apparently failed to make solid contact. That caused the backup computerized controller to be sluggish and experience a slight voltage drop.<br /><br />Moses said a bit of residue likely was the culprit, and repeatedly pushing the circuit breaker in and out knocked it off. "While we don't completely understand the failure ... everybody was comfortable with the residual risk left, that it was an acceptable one to take ... and we're good to fly," said Moses.<br /><br />Aboard Discovery for its 39th and final voyage will be a crew of six veteran astronauts as well as thousands of pounds of supplies, including a humanoid robot. Discovery has carried 180 individuals into orbit over its 26-year career, and logged nearly 150 million miles and more than 5,600 orbits of Earth. It is NASA's oldest surviving shuttle and fleet leader, and will be the first to be prepared for museum retirement.<br /><br />One final shuttle mission is officially on the books for next year as NASA looks toward newer and farther-flying craft. An extra flight may be added.</p>
<p>Mission managers met yesterday afternoon and into the evening to discuss an electrical problem that forced the latest postponement. They concluded the circuit breaker trouble no longer exists and the shuttle is safe to fly. But forecasters warned there is an 80 per cent chance that thunderstorms will keep Discovery on the pad. Liftoff is scheduled for 3:29 p.m. (1929 GMT).<br /><br />The decision came as dark storm clouds rolled over the launch site in Florida, putting some launch preparations on hold. Managers will reconvene before daybreak to assess the weather, before loading the shuttle's fuel tank.<br /><br />"If the forecast tomorrow morning is still as bad as it is today, there's a chance" that today's launch attempt will be called off, mission management team chairman Mike Moses said last night. "It's too early to make that call right now."<br /><br />Discovery's flight to the International Space Station was first stalled by gas leaks last week. Then a problem cropped up Tuesday with a computerized controller for one of the main engines. At this point, the mission is running three days late.<br /><br />The space agency has until Sunday to launch Discovery. Otherwise, it will have to wait until December because of sun angles. Engineers traced the electrical trouble to a circuit breaker that apparently failed to make solid contact. That caused the backup computerized controller to be sluggish and experience a slight voltage drop.<br /><br />Moses said a bit of residue likely was the culprit, and repeatedly pushing the circuit breaker in and out knocked it off. "While we don't completely understand the failure ... everybody was comfortable with the residual risk left, that it was an acceptable one to take ... and we're good to fly," said Moses.<br /><br />Aboard Discovery for its 39th and final voyage will be a crew of six veteran astronauts as well as thousands of pounds of supplies, including a humanoid robot. Discovery has carried 180 individuals into orbit over its 26-year career, and logged nearly 150 million miles and more than 5,600 orbits of Earth. It is NASA's oldest surviving shuttle and fleet leader, and will be the first to be prepared for museum retirement.<br /><br />One final shuttle mission is officially on the books for next year as NASA looks toward newer and farther-flying craft. An extra flight may be added.</p>