Enlarge By John Raoux, AP he crew of space shuttle Discovery, from left, commander Steve Lindsey, pilot Eric Boe, mission specialist's Alvin Drew, Tim Kopra, Michael Barratt and Nicole Stott attend a news conference in front of the shuttle on launch pad 39A at the Kennedy Space Center in Cape Canaveral, Thursday, Oct. 14, 2010. Space shuttle Discovery's engine controllers all worked as expected during overnight testing, but managers still must give a go to pick up a stalled countdown and the weather forecast for a launch attempt Thursday has worsened. Discovery and six astronauts are tentatively scheduled to blast off to the International Space Station at 3:29 p.m. ET Thursday. But engineers still must build a rationale for flying after a back-up engine controller failed to operate as expected during routine prelaunch checkouts on Tuesday. The controller on Engine No. 3 first failed to immediately power up, and then a small but unusual voltage drop was subsequently detected. Engineers believe a trace contaminant likely is the culprit and that repeated power cycling cleared the problem. Each of the shuttle's liquid-fueled main engines is equipped with primary and back-up controllers and all worked as expected during five power-up tests overnight. The suspect controllers has remained powered up since and no voltage irregularities have been detected. The Mission Management Team will be briefed at 2 p.m. ET today, and a decision will be made on whether to proceed with countdown to a launch attempt Thursday. The weather forecast, however, now calls for an 80% chance that rain and thunderstorms would keep the shuttle grounded on Thursday. There is a 40% chance bad weather would prohibit external tank propellant-loading operations, which would pick up about 6 a.m. ET. The bad weather is expected to clear late Thursday, and the forecast for Friday calls for a 60% chance the weather would be acceptable for flight. Winds are expected to pick up and Saturday's forecast calls for a 60% chance conditions would prohibit launch. Guidelines: You share in the USA TODAY community, so please keep your comments smart and civil. Don't attack other readers personally, and keep your language decent. Use the "Report Abuse" button to make a difference. You share in the USA TODAY community, so please keep your comments smart and civil. Don't attack other readers personally, and keep your language decent. Use the "Report Abuse" button to make a difference. Read more