spacetoday.net: Delta 4 investigation continues

Posted: Mon, Jan 24, 2005, 7:36 AM ET (1236 GMT)
Delta 4 Heavy liftoff on first flight (Boeing)

The investigation into the early engine shutdown on the first Delta 4 Heavy flight last month is still in progress and should conclude by the middle of next month. Air Force officials said Friday that a "fault tree" analysis into the incident is underway and that 40 of the 49 branches of that fault tree have been reviewed and excluded as possible causes for the early shutdown. The leading cause remains "cavitation", or the formation of bubbles in the liquid oxygen flow from the propellant tanks to the engine in each of the three common booster cores. Those bubbles led sensors to conclude that the engines had exhausted their supply of liquid oxygen and shut down the engines even though there was still enough propellant to continue the engine burn for its planned duration. Officials believe that the investigation will be concluded by mid-February, but any corrective actions required to fix the problem won't be announced until the investigation concludes. Air Force and Boeing officials remain optimistic that the problem will be resolved in time to permit the first operational Delta 4 Heavy launch later this year, although the investigation has delayed the launch of a single-core Delta 4 from Vandenberg that had been scheduled for the beginning of March.