At noon today, countdown clocks at NASA's Kennedy Space Center in Florida came to life at the T-43 hour mark and immediately began counting down toward a liftoff Tuesday at 10:39 a.m. EDT.
"Discovery is in excellent shape as we complete the troubleshooting from the liquid hydrogen engine sensor cutoff anomaly which caused our first launch attempt scrub on July 13," said NASA test director Pete Nickolenko.
NASA's Kennedy Space Center (KSC) launch team will conduct the countdown from Firing Room 3 of the Launch Control Center. The countdown includes nearly 28 hours of built-in hold time, leading to a preferred launch time at about 10:39 a.m. EDT July 26. The launch opportunity lasts for about five minutes.
Due to concerns about the early development of showers and cumulus clouds, the chance of Kennedy weather prohibiting launch is 40 percent, according to Shuttle Weather Officer Kathy Winters.
If the shuttle fails to lift off in July, NASA will have to wait for the next launch window, September 9-24.
Full coverage: Shuttle Discovery - Return to Flight
Explore further: SpinSat and things that slither splashdown with end of sixth SpaceX mission