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.
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