Thermal analysis of the TMT telescope structure

Cho, Myung‐Haing; Corredor, Andrew; Vogiatzis, Konstantinos; Angeli, George Z.

doi:10.1117/12.857265

Cited by 16 publications

(19 citation statements)

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“…However, it has been reported that the reliability of thermal simulation outputs depends to a large extent on the correct parameterisation of thermal loads which include e.g., T ? , convection coefficient (h) of air temperature and material thermal properties (Cho et al 2009;Cho et al 2010), and thus if possible may have to be validated using real measurements. In this study the latter approach was adopted for the analysis of thermal variations as well as related deformations on the lunar laser ranger (LLR) optical telescope structure based at Hartebeesthoek Radio Astronomy Observatory (HartRAO) located in South Africa.…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…For example, Cho et al (2010) conducted a thermal analysis of the thirty meter telescope (TMT) structure under different predetermined thermal loads for optical performance over day and night temperatures spanning three consecutive days. The study discovered structural thermal variations ranging between 0.01 and 7.32°C corresponding with thermally-induced deformations ranging between 141 and 993 lm respectively (Cho et al 2010), and thus were shown to have a temporal impact on telescope pointing with offsets ranging from 0.7 00 to 1 00 at selected elevation angles (Vogiatzis et al 2014). Mittag et al (2008) analysed the influence of ambient air temperatures on the pointing of the Hamburg robotic optical telescope for 16 nights (with temperatures ranging from -6.4 to 25.8°C) and found that thermal expansion of component materials primarily triggered misalignments of the optical axis with the tube.…”

Section: Introductionmentioning

confidence: 99%

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Thermal analysis of the LLR optical telescope tube assembly based in Hartebeesthoek Radio Astronomy Observatory

et al. 2015

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The Hartebeesthoek Radio Astronomy Observatory of South Africa is currently developing a lunar laser ranger (LLR) system based on a one metre aperture telescope in collaboration with National Aeronautics and Space Administration and the Observatoire de la Côte d'Azur. This LLR will be an addition to a limited list of operating LLR stations globally and it is expected to achieve sub-centimetre range precision to the Moon. Key to this expectation including the overall telescope operational performance is thermal analysis of the telescope structure, based on the thermal properties of component materials and their interaction with the environment through conventional heat transfer mechanisms. This paper presents transient thermal simulation results of the telescope's optical tube and one metre primary mirror in terms of thermal variations and consequent structural deformations. The results indicate that on a non-windy, cloud-free and winter day, the temperature gradients on the structure could be within 1°C with respect to the temporal ambient air temperatures at the site when these are between 9 and 23°C. Furthermore, these gradients were coupled with thermally-induced total deformations that vary between 2.9 and 40.7 lm of the assembled telescope components. In overall, these findings suggest that both the tube and especially the mirror may respond very slowly to ambient temperatures; however, correcting for structural thermal variations is imperative in maximizing the pointing accuracy of the telescope thereby increasing the chance being on-target with the retroreflectors located on the Moon surface.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Thermal analysis of the LLR optical telescope tube assembly based in Hartebeesthoek Radio Astronomy Observatory

et al. 2015

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“…They include CFD simulations of the observatory on the TMT site [12], the radiation-convection enclosure skin temperature model, and the solid thermal models of the optical elements [14], their support structure and the telescope structure [15].…”

Section: Image Quality Error Budgetmentioning

confidence: 99%

Statistical approach to systems engineering for the Thirty Meter Telescope

Angeli

Vogiatzis

2010

SPIE Proceedings

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Core components of systems engineering are the proper understanding of the top level system requirements, their allocation to the subsystems, and then the verification of the system built against these requirements. System performance, ultimately relevant to all three of these components, is inherently a statistical variable, depending on random processes influencing even the otherwise determinjstic components of performance, through their input conditions. The paper outlines the Stochastic Framework facilitating both the definition and estimate of system performance in a consistent way. The environmental constraints at the site of the observatory are significant design drivers and can be derived from the Stochastic Framework, as well. The paper explains the control architecture capable of achieving the overall system performance as well as its allocation to subsystems. An accounting for the error and disturbance sources, as well as their dependence on environmental and operational parameters is included. The most current simulations results validating the architecture and providing early verification of the preliminary TMT design are also summarized.

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“…A 3-year environmental record [3] measured on 13N, Mauna Kea, the TMT site, provides ambient condition variability and the corresponding telescope pointing record from Gemini orth provides orientation statistics. The CFD models provide heat transfer coefficients to the Segment Support Assembly (SSA), M21M3 and telescope structure FE solid thermal models [4,5], which in turn provide temperature and heat fluxes to the CFD models as boundary conditions for the telescope and optical surfaces. The surface thermal model provides heat fluxes to the CFD models for the enclosure surfaces.…”

Section: Introductionmentioning

confidence: 99%

Thermal modeling environment for TMT

Vogiatzis

2010

SPIE Proceedings

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In a previous study we had presented a summary of the TMT Aero-Thermal modeling effort to support thermal seeing and dynamic loading estimates. In this paper a summary of the current status of Computational Fluid Dynamics (CFD) simulations for TMT is presented, with the focus shifted in particular towards the synergy between CFD and the TMT Finite Element Analysis (FEA) structural and optical models, so that the thermal and consequent optical deformations of the telescope can be calculated. To minimize thermal deformations and mirror seeing the TMT enclosure will be air conditioned during day-time to the expected night-time ambient temperature. Transient simulations with closed shutter were performed to investigate the optimum cooling configuration and power requirements for the standard telescope parking position. A complete model of the observatory on Mauna Kea was used to calculate night-time air temperature inside the enclosure (along with velocity and pressure) for a matrix of given telescope orientations and enclosure configurations. Generated records of temperature variations inside the air volume of the optical paths are also fed into the TMT thermal seeing model. The temperature and heat transfer coefficient outputs from both models are used as input surface boundary conditions in the telescope structure and optics FEA models. The results are parameterized so that sequential records several days long can be generated and used by the FEA model to estimate the observing spatial and temporal temperature range of the structure and optics. Keywords : Extremely Large Telescopes, Thermal Modeling, Computational Fluid Dynamics INTROD UCTIONThermal Management is a key aspect of Wave-front Control Architecture. Approximately 30% of the total seeing limited error budget allocation has aero-thermal causes, with 80% of that attributed to thermal seeing and deformations. As tools to minimize thermal effects TMT uses air-conditioning during day-time, passive ventilation during night-time and heat release control in various forms (sub-system cooling, proper location of heat sources, coatings of desired emissivity). The optimization of the configuration and operation of these tools is done by modeling and is beyond the scope of this paper. However, once these tools have been incorporated in the design, they create a more stable thennal environment for the telescope structure and the optics and different active optics correction scenarios can be modeled. Figure I depicts the current TMT aero-thermal modeling synergy. The gray box called "Stochastic Framework" represents the TMT Monte Carlo simulation test-bed [I] and fuses together performance estimates for optical surface shapes, wind disturbances and thermal seeing. It utilizes the normalized Point Source Sensitivity (PSSn) performance metric [2]. A 3-year environmental record [3] measured on 13N, Mauna Kea, the TMT site, provides ambient condition variability and the corresponding telescope pointing record from Gemini orth provides orientation statistics. The ...

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Thermal analysis of the TMT telescope structure

Cited by 16 publications

References 5 publications

Thermal analysis of the LLR optical telescope tube assembly based in Hartebeesthoek Radio Astronomy Observatory

Thermal analysis of the LLR optical telescope tube assembly based in Hartebeesthoek Radio Astronomy Observatory

Statistical approach to systems engineering for the Thirty Meter Telescope

Thermal modeling environment for TMT

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