On Thursday, NASA canceled the inaugural test flight for their new Orion spacecraft, which they hope will eventually produce manned missions to Mars, after fill and drain valve issues prior to the launch. Now delayed until Friday morning, the Orion will take-off while attached to a Delta IV Heavy rocket.
Cycling the fill and drain valves showed that the core booster valve for the hydrogen tank was not showing as it should for launch. While these issues are considered minor, they could not be resolved before the launch window closed, just before 10 a.m. Thursday morning.