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Comment by catherd | Hacker News Reader

I worked on some of the automated machinery that manufactured these, and the scale of it all really is impressive.

It was fun building a robot bigger than most houses. We had to be careful to design it in small and light enough pieces that they could be safely transported to the final install location. Any time we talked to a supplier about a widget to go on the machines, it was always "What is the biggest X you make? OK, we need that one."

The wing assembly bay was built on a scale such that the curvature of the earth was an important factor in our machine install process.

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I imagine that produced a few funny conversations, that combined with the inevitable "I will take all of the ball screws that you have available, thank you" call.

The worst issue we had was competing with the windmill people for giant bearings. We were actually ordering those 1.5 years out at one point, for machines that no one had ordered and weren't designed yet.

At least you could sell them on to the windmill people if you never got an order for said machine, I guess.

"Wait…I'm worried what you just heard was give me a lot of balls screws. What I said..."

Was it the curvature of the coordinate system you were using during machine install, or was it the actual curvature of earth's surface that was important here?

The actual curvature of the earth is what mattered. We used both laser interferometers and highly precise levels as part of the install.

If you assume the vertical axis and gravity are aligned, over the distances our machines moved the deviation between the two is enough to matter when setting up the machine alignment. The measurements would only match if you accounted for the curvature of the earth.

> If you assume the vertical axis and gravity are aligned

Gravity's vector is not the same as earth's surface-normal though - if you stand at the base of Mt. Everest then gravity is slightly angled compared to the curvature of the earth at that point.

There isn't really a local good reference for "earth's surface normal" at the scale we're talking here anyway, though - it seems that what matters is the divergence between the gravity vector at one end of the factory and the other.

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