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Segment Alignment For The Keck Telescope Primary Mirror

We propose to use a Shack-Hartmann camera to align and phase the thirty-six segments of the ten meter primary mirror of the Keck Telescope. Tilt errors are determined by employing the Shack-Hartmann device in a manner exactly analogous to that used in mirror testing and in adaptive optics. Piston errors are determined (with the same device) by exploiting diffraction effects near the intersegment edges. These two tests are shown to have sensitivities that are comparable to each other and that are sufficient to achieve the design goals of the telescope. We describe how the tilt test can be extended to give information both about the individual segment figures and about the global mirror parameters. Some of the complications and potential systematic effects associated with these tests are discussed.