What is a raceway?
A raceway is the external ducting used to route plumbing and cabling between the top and bottom of a rocket.
They could be routed internally, but in most cases the skin of the rocket is also the skin of the a fuel tank, or there is limited space between the two. It also makes access to items such as the FTS far easier in the days before launch.
You can see them working on the inside of one of the previous boosters before launch.
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