SpaceX was able to analyze the engines’ startup behavior in McGregor, and additional inspections found a blockage in a narrow line leading to a relief valve on the gas generator.
Koenigsmann said the vent port, which means just one-sixteenth of an inch wide, was obstructed by a hardened masking lacquer. He said liquid lacquer — similar to red nail polish — is used by a third-party vendor that anodizes aluminum engine components for SpaceX.
The lacquer protects certain parts during the anodizing treatment process, but the vendor — which officials did not identify — is supposed remove the material before shipping the components to SpaceX for engine manufacturing.
The gas generator on each Merlin engine drives a turbopump feeding kerosene and liquid oxygen propellants into the main combustion chamber.
“It’s obviously a very important part,” Koenigsmann said. “That little red substance was blocking a relief valve that caused it to (ramp up pressure) a little bit earlier than it was supposed to.”
“Probably during the washing or the cleaning process some of that masking lacquer went into this vent hole and blocked it,” Koenigsmann said.
“How was this missed? The little borehole that goes to the vent valve is tiny. It’s 60 thousandths of an inch … When something goes in there and is hung in there, it’s possible you miss it,” Koenigsmann said. “You shouldn’t … but I can see how people overlook that and didn’t quite see that, even if it is red.”