Delta IV Root Cause

According to the following press release, the Delta IV
failure investigation process will continue through the
end of March, at least. Boeing "has started to take
steps toward corrective actions for the *entire* Delta IV
fleet", which presumably includes the Delta IV-M for
NASA's GOES launch currently schedule for early May.

"http://www.losangeles.af.mil/smc/pa/releases/2005/index.html"

"SPACE & MISSILE SYSTEMS CENTER (AFSPC)
Office of Public Affairs
Release no: 03-01-05
Date: March 16, 2005
For Immediate Release
Los Angeles Air Force Base, Calif.

Root Cause Declared for Delta IV Heavy Demo Mission

The Boeing Company and the Air Force, supported by The Aerospace
Corporation, as part of their on-going investigation, have identified
the root cause for the premature Main Engine Cut-Off (MECO) on the
Delta IV Heavy Lift Vehicle (HLV) demonstration mission that was
launched Dec. 21, 2004.

The root cause of the anomaly has been identified as a fluid cavitation
within the liquid oxygen feed system. Analyses show that the
cavitation originated at the entrance of the propellant feedline, where
a filtration screen and turning elbow restrict the propellant flow as
it accelerates leaving the tank. This feedline restriction has been
present in all previous Delta IV flights, but the unique combination of
vehicle acceleration, liquid level in the tank, and propellant flow
rate for this mission, reduced the fluid pressure enough to enable the
creation of gaseous oxygen at this location as the tanks emptied.
Further draining of the liquid oxygen tank worsened the conditions at
the feedline inlet, causing the cavitation effect to extend down the
feedline until it reached the liquid depletion sensors and caused them
to momentarily toggle dry. This action was sensed by the flight
computer, which initiated the sequence to throttle-down and shut off
the main engines as it is programmed to do. Flight data shows that
sufficient propellant remained in the tank to complete the planned
first stage burn time.

.....

The Boeing Company has started to take steps toward corrective actions
for the entire Delta IV fleet. Additional computer simulations that
fully analyze the liquid oxygen flow between the bottom of the
propellant tank and the engine cut-off sensors will continue through
March to help the engineers select and validate corrective actions. A
final executive review board will then be held to officially close the
anomaly investigation."

- Ed Kyle