Previous studies of the scaling of the costs of ground based optical observatories suggest that total costs scale as the
primary mirror diameter to a power between 1.7 and 3.0. It has been suggested that observatory costs may scale as
primary mirror diameter squared reflecting the dependence on thinner mirrors in the current generation of observatory
design. Upon completing the detailed cost estimate in support of the Preliminary Design for the Thirty Meter Telescope,
an in depth study was undertaken to understand the sensitivity of the estimate to mirror diameter and thickness in
addition to other leading parameters of TMT such as segmentation, primary focal ratio, and enclosure diameter. Based
upon this analysis, and expressing the costs scaled solely to the mirror diameter, our analysis suggests that the TMT
design scales effectively as the diameter to the power 1.2. We will describe the assumptions used to guide this study, the
methods used to build the cost model, and the general results of the model.
Estimates of the cost to construct the Thirty Meter Telescope (TMT) have progressed from rough order parametric analyses at the early Reference Design stage to detailed bottom up estimating at the lowest levels of the TMT Work Breakdown Structure during the Conceptual and Preliminary Design phases. This detailed estimating process is guided by uniform estimating procedures and a contingency estimating methodology that assesses technical, cost and schedule risks for each item that is estimated. Details of the cost estimating techniques, their implementation, uses of the results, and planned next steps will be described.