The new deployable tertiary mirror for the Keck I telescope (K1DM3) at the W. M. Keck Observatory has been assembled, tested and shipped to the telescope site, and is currently being installed. The mirror is capable of reflecting the beam to one of six positions around the telescope elevation ring or to retract out of the way to allow the use of Cassegrain instruments. This new functionality is intended to allow rapid instrument changes for transient event observations and improve telescope operations. This paper presents the final as-built design. Additionally, this paper presents detailed information about our alignment approach in the attempt to duplicate the instrument pointing orientation of the existing M3.

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C. Ratliff, G. Cabak, A. Phillips, X. Prochaska, W. Deich, D. Sandford, J. Nelson, D. Cowley, A. Tripsas, M. Bolte, S. Park, M. Peck, P. Zachary, T. Wold, M. Dahler, M. Kassis, A. Vandenberg, and J. Ward, "Fabrication completion and commissioning of a deployable tertiary mirror for the Keck I Telescope," Proc. SPIE 10706, Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation III, 1070611 (Presented at SPIE Astronomical Telescopes + Instrumentation: June 12, 2018; Published: 10 July 2018); https://doi.org/10.1117/12.2312207.