Repairs to the W.M. Keck Observatory primary mirror segments are needed to stop the cracking at the bonded supports. The repairs include changes to the design of the axial and radial inserts and the way these are bonded to the mirror backsurface. In this paper, we present finite element analyses of a primary mirror segment including whiffletree and radial mirror support system to determine the effect of the modified supports on the mirror figure. Displacements of the front surface are calculated for a number of operational and assembly fit-up cases, and differential displacements between the old and new support system are found. Zernike coefficients are calculated for front surface displacements and differential displacements. Stresses on the glass surface at the radial pad bond locations are also determined. The results show that the residual deformations of the mirror front surface with the new supports are similar to those with the old supports, differing only in the immediate vicinity of the axial inserts and radial pads, and the impact on the image quality of the Keck telescopes is negligible.
On 15 October 2006, a large earthquake damaged both telescopes at W. M. Keck Observatory resulting in weeks of observing downtime. A significant portion of the downtime was attributed to recovery efforts repairing damage to telescope bearing journals, radial pad support structures, and encoder subsystems. To reduce the risk of damage and loss of observing time in future seismic events, we developed a conceptual design for the seismic upgrade of the twin Keck Telescopes. The paper covers the design requirements and constraints for the seismic upgrade, the evaluation method used to check the safety of sensitive components, and the trade-off study used to compare different options and to select the best design. Various design options such as base isolating the structure, strengthening seismic restraints, adding dampers, adding break-away mechanisms, and combinations of these design options are considered in this study. Nonlinear time history analyses are performed to evaluate the performance of the design concepts.