NASA looks for source of debris found in ET feedline

NASA engineers are looking into how a metal washer ended up in the liquid oxygen feedline of an external tank scheduled for use by the shuttle Endeavour next February.

While mesh screens in the main propulsion system plumbing are in place to prevent "foreign object debris," or FOD, from entering a shuttle main engine, such debris could, in theory, puncture a propellant line in the high-flow-rate operating environment. Engineers want to make sure no other debris is present in external tank No. 138.

Engineers inspecting external tank 138 found a
metal washer in a liquid oxygen feed line.
(Photo: NASA)

External tanks feature a liquid oxygen tank at the top and a larger liquid hydrogen tank at the bottom. The propellants are fed into the shuttle's main propulsion system through 17-inch-wide feed lines before branching out to three main engines. During engine operation, nearly 2,800 pounds of liquid oxygen are consumed per second.

The washer in question was found during initial inspections of ET-138 after its arrival at the Kennedy Space Center. Endeavour and ET-138 are scheduled for launch Feb. 26 to deliver supplies to the International Space Station, along with a $1.5 billion physics experiment.

Metallic foreign object debris is always a concern in the extreme operating environment of the space shuttle's main propulsion system. The washer does not pose a significant combustion threat, engineers say, but the high flow rates could cause a propellant line puncture in a worst-case scenario. The washer has been returned to the Michoud Assembly Facility near New Orleans, where the external tanks are built, for analysis.

External tank No. 138 undergoing initial inspections
at KSC. (Photo: NASA)