spacetoday.net: Delta 4 Heavy flaw identified

Posted: Thu, Mar 17, 2005, 7:39 AM ET (1239 GMT)
Delta 4 Heavy liftoff on first flight (Boeing)

The US Air Force said Wednesday that "cavitation" in a liquid oxygen feed line was the root cause for the premature shutdown of the main engines on the inaugural Delta 4 Heavy flight last December. According to an Air Force statement, cavitation — the formation of pockets of gaseous oxygen — started at the entrance of the liquid oxygen feedline where the nature of the propellant line restricts the flow of propellant. The cavitation then extended down the line until it reached sensors, which momentarily registered a lack of propellant, triggering a shutdown of the engines even though there was still some liquid oxygen flowing. The feedline restriction that caused the cavitation existed on all previous Delta 4 launches, but the acceleration and propellant flow conditions unique to the Delta 4 Heavy triggered the cavitation. Cavitation had been the leading cause for the engine shutdown for some time, but investigators wanted to rule out all other possibilities before reaching a final conclusion. Boeing is already working on corrective actions that will cover all variants of the Delta 4. The statement didn't indicate if the changes would affect the scheduled launches of the Medium or Heavy versions of the Delta 4 scheduled for this year; the next Delta 4 Medium launch is scheduled for early May while the Heavy variant is scheduled to fly later this year.