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The Soviets allegedly used the same principle to make cheap single sensor missile seeker heads.

Two DOF: two sensors?

If the missile is spinning, you can do it with one. The original Sidewinder air to air missile worked that way.

And now the name 'sidewinder' makes perfect sense

While it may have been a secondary reason, it's named after the snake for the sensory "heat seeking" attribute: https://en.wikipedia.org/wiki/Crotalus_cerastes

I had always assumed it was due to the use of roller stabilized fins / rollerons.

Neat, thanks. I should have thought of that.