scope:

Description of Driving Event:

The SSME vertical installer is used to position the engine for mounting on or removal from the orbiter. During SSME vertical installer operations, it was discovered that the air piston had a scored land ring. This scoring was due to the end of the stop groove being peened over. This peened condition happened when the stops came into hard contact with the end of the grooves. This condition occurs when the piston sticks in the cylinder due to a lack of lubrication and/or foreign material in the cylinder. Pressure then builds up until the piston breaks free. When the piston breaks free it can travel to the stops with enough momentum to cause this peening condition. A failure of the vertical installer caused by this scoring/peening could prevent positive control over the SSME and lead to unexpected movement during the installation/removal process.