NASA, with reference to the SpaceX statement, announced the official reason for canceling the launch of the Falcon 9 rocket, which was scheduled for October 2 of this year. A month-long investigation revealed that the launch escaped from a tiny drop of varnish only 2mm in diameter, which disrupted the rocket's safety valve. But the most worrying thing is that none of the agency's specialists and contractor engineers understand how this happened.
During the launch of the Falcon 9 rocket, a false start occurred - for some reason, out of nine engines of the first stage, two of the ignition turned on earlier than expected. This does not apply to extreme situations, but NASA decided to play it safe. The launch was canceled, the engines were removed and sent to the test site. There, it turned out that the safety valve was blocked by a drop of varnish, due to which the gas generator worked ahead of schedule. The varnish was removed and the engine started working again as usual.
The origin of the varnish was quickly established - it is a protective coating that is applied to aluminum parts before anodizing, and which must then be removed. Probably, a droplet with a diameter of only 2 mm was simply not noticed, but it ended up in exactly the place where it managed to disrupt the operation of the entire huge engine. Engineers checked all the built engines for the next SpaceX missions and found two more similar defects, which caused the start of Crew-1 to be postponed.
The varnish incident is both surprising and alarming because nothing like this has ever happened to a Merlin before. Over the past decade and a half, SpaceX has created and launched hundreds of such engines into space, but this is the first time it has encountered such a problem.