At 22:52 UTC another launch attempt of the Space Shuttle Discovery has been scrubbed after the fill-and-drain valve inside space shuttle Discovery’s aft compartment developed a problem during the External Tank (ET) tanking. STS-128 Flight Director Pete Nikolenko gave the order to stop the taking of ET with liquid hydrogen after the fill-and-drain value failed to close when instructed. The valve is actually two valves in series, one outboard and one inboard. Both need to be closed for the flight, but if they malfunction in the closed state, NASA would not be able to drain the tank (after a scrub or a delay).
Although the next launch windows open on Thursday at 04:42:49 UTC (with preferred launch time at 04:47:49) and on Friday at 04:17:07 UTC (launch targeted for 04:22:07), the date and time of the next launch attempt are currently unknown. NASA engineers need to first gather data and to determine whether there was an actual problem with the valve itself or a faulty indicator was the culprit tonight.
Update: Despite several launch windows with favorable ISS orbit alignment in the following days, Discovery’s last day to attempt the launch before mid-October is August 31 (at 03:11:21 UTC). Once the August 31 window closes (at 03:16:21 UTC) Discovery wouldn’t be able to undock before the Japanese and Russion missions arrive at the ISS.