Tanking operations began on time at 7:25 a.m. EST, and slow filling of liquid hydrogen is under way. The three-hour fueling process will provide the fuel and oxidizer Discovery’s three main engines require for the 8 1/2-minute trip to orbit. Launch is scheduled for 4:50 p.m. It takes about three hours to fill the tank, then the final inspection team will survey the shuttle stack on the launch pad for ice buildup or other abnormalities.