Engineers to Test Valve This Evening

The boil off of the remaining liquid hydrogen and liquid oxygen in space shuttle Discovery's external tank was completed at about 1:40 p.m. EDT today. Crews have begun inerting the tank with helium gas to flush out any remaining hydrogen gas. They expect the process to be completed at about 5:30 p.m.

Following inerting, engineers will begin evaluating and testing the liquid hydrogen fill and drain valve in the shuttle's main propulsion system by opening and closing it.

This morning's launch attempt was postponed after an indication that valve failed to perform as expected during fueling of the shuttle's external tank Tuesday afternoon.

NASA is targeting Discovery's next launch attempt for no earlier than Friday, Aug. 28 at 12:22 a.m., depending on the results of the testing. The weather forecast calls for a 70 percent chance of acceptable conditions at launch time.