For future giant telescopes, control of construction and operation costs will be the key factor in their success. The best way to accomplish this cost control, while maximizing the performance of the telescope, will be through design-to-cost methods that use value engineering techniques to develop the most cost-effective design in terms of performance per dollar. This will require quantifiable measures of performance and cost, including: (1) a way of quantifying science value with scientific merit functions; (2) a way of predicting telescope performance in the presence of real-world disturbances by means of integrated modeling; and (3) a way of predicting the cost of multiple design configurations.Design-to-cost methods should be applied as early as possible in the project, since the majority of the life-cycle costs for the observatory will be locked in by choices made during the conceptual design phase. However, there is a dilemma: how can costs be accurately estimated for systems that have not yet been designed? This paper discusses cost estimating methods and describes their application to estimating the cost of ELTs, showing that the best method to use during the conceptual design phase is parametric cost estimating. Examples of parametric estimating techniques are described, based on experience gained from instrument development programs at NOAO.We then describe efforts underway to collect historical cost information and develop cost estimating relationships in preparation for the conceptual design phase of the Giant Segmented Mirror Telescope.
One of the critical design factors for large telescopes is control of primary mirror distortion caused by wind pressure variations. To quantify telescope wind loading effects, the Gemini Observatory has conducted a series of wind tests under actual mountaintop conditions. During commissioning of the southern Gemini Telescope, simultaneous measurements were made of pressures at multiple points on the mirror surface, as well as wind velocity and direction at several locations inside and outside the dome. During the test we varied the dome position relative to the wind, the telescope elevation angle, the position of windscreens in the observing slit, and the size of the openings in the ventilation gates. Five-minute data records were made for 116 different test conditions, with a data-sampling rate of ten per second. These data sets have been processed to provide pressure maps over the surface of the mirror at each time instant. From these pressure maps, the optical surface distortions of the primary mirror have been calculated using finite-element analysis. Data reduction programs have been developed to enhance visualization of the test data and mirror surface distortions. The test results have implications for the design of future large telescopes.
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