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Will shuttle Discovery be cleared for launch Thursday? BY WILLIAM HARWOOD STORY WRITTEN FOR CBS NEWS "SPACE PLACE" & USED WITH PERMISSION Posted: November 3, 2010 
With the shuttle Discovery's countdown on hold, engineers reviewed historical data and refined a "fault tree" to understand what caused irregularities in a critical circuit Tuesday, delaying launch to at least Thursday.
While the weather forecast does not normally play a roll in launch decisions, it could be a factor in this case. Meteorologists are predicting dismal conditions Thursday with high winds expected Friday and Saturday. With a frontal system moving through the area, forecasters are predicting an 80 percent chance of low clouds and rain that would prohibit a launching Thursday. High winds are expected Friday and Saturday, with forecasters putting the odds of acceptable weather at 60 percent and 40 percent respectively. The shuttle's current launch window runs through Sunday, with a possible extension to Monday. If Discovery isn't off the ground by then, launch would slip to Dec. 1, the opening of the year's final shuttle launch window. If the MMT decides to proceed with a Thursday launch attempt, engineers will roll a protective gantry away from Discovery around 7 p.m. Wednesday, exposing the orbiter to view and setting the stage for the start of fueling at 6:04 a.m. Thursday. Discovery's six-member crew -- commander Steven Lindsey, pilot Eric Boe, Michael Barratt, Nicole Stott and spacewalkers Timothy Kopra Alvin Drew -- would begin strapping in around 12:09 p.m. to await liftoff at 3:29:43 p.m. Assuming an on-time liftoff, Lindsey would guide Discovery to a docking with the International Space Station around 11:29 a.m. on Nov. 6. Spacewalks by Kopra and Drew would be scheduled for Nov. 8 and 10. If all goes well, Discovery would undock from the lab complex around 5:27 a.m. on Nov. 13, setting up a landing back at the Kennedy Space Center at 10:24 a.m. on Nov. 15.
Each main engine is equipped with a controller that monitors engine operation -- valve positions, temperatures, pressure, vibration and other factors -- 50 times per second. Those data are fed to the shuttle's flight computers and if a problem develops, an engine can be safely shut down before a catastrophic failure occurs. Engineers suspect the electrical anomalies in the backup channel of main engine No. 3's controller were the result of "transient contamination" in a circuit breaker. The breaker in question was cycled five times overnight and the circuit was used to power up the shuttle's master events controllers. The engine controller has operated normally ever since it was activated. But Mike Moses, chairman of the mission management team, said Tuesday that engineers needed to come up with an explanation of what went wrong in the first place and develop a solid flight rationale before Discovery will be cleared for launch. "Does it make sense that a circuit breaker with a little bit of a bad contact explains both of these signatures that we saw? The community feels pretty confident that that is the case, but they do need time to polish that story," Moses said Tuesday. He emphasized that NASA would not let the relatively short launch window drive a decision to launch Discovery if the engineering data do not support show it is safe to do so. "If tomorrow we come in and go we either still don't understand it or we understand it and we need to fix it, then we're going to do that," he said. "We're not just going to fly as is."
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The official embroidered crew patch for shuttle Discovery's final flight is available in our store. Free shipping to U.S. addresses!
