In the past month I have seen bumper stickers with the initials for something like NBL and RCC. I read those as Neutral Buoyancy Laboratory and Reinforced-Carbon-Carbon.
For those who don't what these here are some definitions and images.
The Neutral Buoyancy Laboratory is the giant pool where astronauts train.
Reinforced-Carbon-Carbon is a well-suited to structural applications at high temperatures, or where thermal shock resistance and/or a low coefficient of thermal expansion is needed. It is found on the nose cone, the leading edges of the wings, the bottom, and the leading edge of the vertical stabilizer of the orbiter
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