Micro solenoid valve-Flow Control Valve Investigation reveals probable cause of failure

A one-year long investigation into the Micro solenoid valveliberation of part of a Flow Control Valve (FCV) poppet during Special cylinderEndeavour’s STS-126 launch in November 2008 has concluded with a recommendation to close the official investigation Air gun after findings revealed the most probable cause of the STS-126 liberation and subsequent eddy current reading increases following some of the Shuttle missions last year.

Review of the Issue:

During Endeavour’s launch on November 14, 2008, “MPS (Main Propulsion System) engine #2 GH2 (Gaseous Hydrogen) flow control valve (FCV) LV57 appeared to transition from low flow towards high flow position without being commanded to do so,” notes the FCV Poppet Investigation Summary presentation to the Program Requirements Control Board (PRCB) on January 7.

Post-flight inspections of the valve revealed a liberation of ~87-degrees of the poppet head’s circumference.

This finding lead to the immediate inspection of the FCVs throughout the Shuttle fleet and the subsequent grounding of Discovery and the STS-119 mission until the cause of the poppet liberation could be determined or the integrity of the FCVs to set to fly with Discovery verified.