We present the details of an experimental apparatus built to explore wavefront distortion and its mitigation when an optical beam passes from one thermal environment into another. The experiment simulates a situation within the Advanced Technology Solar Telescope (ATST) baseline design where the beam travels from an ambient-temperature environment into a thermostatically controlled "room temperature" environment. We found that an 8°C temperature difference between the two environments introduces about 125 nm rms of wavefront distortion. A double air curtain (one on each side of the boundary) reduces this to about 30 nm rms. We also showed that the high-order (>1300 DoF) adaptive optics system which is integral to the ATST design will be able to further reduce this to about 5 nm rms, well within our initial error budget.
KEYWORDS: Thermal modeling, Telescopes, Systems modeling, Convection, Solar radiation models, Solar telescopes, Cooling systems, Control systems, Camera shutters, Observatories
Telescope enclosure design is based on an increasingly standard set of criteria. Enclosures must provide failsafe protection in a harsh environment for an irreplaceable piece of equipment; must allow effective air flushing to minimize local seeing while still attenuating wind-induced vibration of the telescope; must reliably operate so that the dome is never the reason for observatory down time; must provide access to utilities, lifting devices and support facilities; and they must be affordable within the overall project budget. The enclosure for the Advanced Technology Solar Telescope (ATST) has to satisfy all these challenging requirements plus one more. To eliminate so-called external dome seeing, the exterior surfaces of the enclosure must be maintained at or just below ambient air temperature while being subjected to the full solar loading of an observing day. Further complicating the design of the ATST enclosure and support facilities are the environmental sensitivities and high construction costs at the selected site - the summit of Haleakala on the island of Maui, Hawaii. Previous development work has determined an appropriate enclosure shape to minimize solar exposure while allowing effective interior flushing, and has demonstrated the feasibility of controlling the exterior skin temperature with an active cooling system. This paper presents the evolution of the design since site selection and how the enclosure and associated thermal systems have been tailored to the particular climatic and terrain conditions of the site. Also discussed are load-reduction strategies that have been identified through thermal modeling, CFD modeling, and other analyses to refine and economize the thermal control systems.
KEYWORDS: Telescopes, Control systems, Mirrors, Wavefronts, Adaptive optics, Observatories, Control systems design, Buildings, Interfaces, Solar telescopes
The four-meter Advanced Technology Solar Telescope (ATST) will be the most powerful solar telescope and the world's leading resource for studying solar magnetism that controls the solar wind, flares, coronal mass ejections and variability in the Sun's output. Development of a four-meter solar telescope presents many technical challenges (e.g., thermal control of the enclosure, telescope structure and optics). We give a status report of the ATST project (e.g., system design reviews, instrument PDR, Haleakala site environmental impact statement progress) and summarize the design of the major subsystems, including the telescope mount assembly, enclosure, mirror assemblies, wavefront correction, and instrumentation.
The four-meter Advanced Technology Solar Telescope (ATST) will be the most powerful solar telescope and the world's leading resource for studying solar magnetism that controls the solar wind, flares, coronal mass ejections and variability in the Sun's output. Development of a four-meter solar telescope presents many technical challenges, which include: thermal control of optics and telescope structure; contamination control of the primary mirror to achieve low scattered light levels for coronal observations; control of instrumental polarization to allow accurate and precise polarimetric observations of solar magnetic fields; and high-order solar adaptive optics that uses solar granulation as the wavefront sensing target in order to achieve diffraction limited imaging and spectroscopy. We give a status report of the ATST project focusing on the substantial progress that has been made with the design of the ATST. We summarize the design of the major subsystems, including the enclosure, the primary and secondary mirror assemblies, the coude and Nasmyth focal stations, adaptive optics and instrumentation. The site selection has been successfully concluded and we discuss areas where the site selection impacts the design.
KEYWORDS: Telescopes, Adaptive optics, Optical instrument design, Polarization, Solar telescopes, Polarimetry, Mirrors, Visible radiation, Space telescopes, Control systems design
The Advance Technology Solar Telescope (ATST) has finished its conceptual design stage, submitted a proposal for construction funding and is working towards a system level preliminary design review later this year. The current concept (including integrated adaptive optics and instrumentation) will be reviewed with concentration on solutions to the unique engineering challenges for a four meter solar telescope that have been previously presented. The overall status will be given with a concentration on near term milestones and impact on final completion targeted in 2012.
KEYWORDS: Convection, Thermal modeling, Solar radiation models, Data modeling, Telescopes, Monte Carlo methods, Temperature metrology, Error analysis, Gemini Observatory, Francium
The enclosure for the Advanced Technology Solar Telescope (ATST) is both a wind shield and a source of seeing. Its design must minimize self-induced seeing while remaining within cost constraints and balancing with other error budget items. We report the methods used to quantify seeing performance, including thermal modeling, seeing estimation, and systems engineering error budgets. Thermal modeling is performed using a commercial software package that applies measured site weather data to a CAD-generated enclosure model. Seeing estimation is performed using a simple aerodynamic treatment. The results, along with measured site wind and temperature distributions, are combined into a "bottom-up" performance prediction using Monte Carlo techniques.
The 4m ATST will be the most powerful solar telescope in the world, providing a unique scientific tool to study the Sun and other astronomical objects. The design and development phase for the Advance Technology Solar Telescope (ATST) is progressing. The conceptual design review (CoDR) for the ATST is scheduled for August 2003. We present a brief description of the science requirements of ATST, and remind the reader of some of the technical challenges of building a 4-m solar telescope. We will discuss some of the design strategies that will allow us to achieve the required performance specifications, present conceptual designs for the ATST, and summarize the results of trades we have made on our path to the CoDR. The thermal impacts to local, self-induced seeing with respect to some of our system level trades that have been completed will be discussed.
High-resolution studies of the Sun's magnetic fields are needed for a better understanding of solar magnetic fields and the fundamental processes responsible for solar variability. The generation of magnetic fields through dynamo processes, the amplification of fields through the interaction with plasma flows, and the destruction of fields are still poorly understood. There is still incomplete insight as to what physical mechanisms are responsible for heating the corona, what causes variations in the radiative output of the Sun, and what mechanisms trigger flares and coronal mass ejections. Progress in answering these critical questions requires study of the interaction of the magnetic field and convection with a resolution sufficient to observe scales fundamental to these processes.
The 4m aperture Advanced Technology Solar Telescope (ATST) will be a unique scientific tool, with excellent angular resolution, a large wavelength range, and low scattered light. With its integrated adaptive optics, the ATST will achieve a spatial resolution nearly 10 times better than any existing solar telescope. Building a large aperture telescope for viewing the sun presents many challenges, some of the more difficult being
Heat control and rejection
Contamination and scattered light control
Control of telescope and instrument polarization
Site selection
This talk will present a short summary of the scientific questions driving the ATST design, the design challenges faced by the ATST, and the current status of the developing design and siting considerations
The 4m Advance Technology Solar Telescope (ATST) will be the most powerful solar telescope in the world, providing a unique scientific tool to study the Sun and possibly other astronomical objects, such as solar system planets. We briefly summarize the science drivers and observational requirements of ATST. The main focus of this paper is on the many technical challenges involved in designing a large aperture solar telescope. The ATST project has entered the design and development phase. Development of a 4-m solar telescope presents many technical challenges. Most existing high-resolution solar telescopes are designed as vacuum telescopes to avoid internal seeing caused by the solar heat load. The large aperture drives the ATST to an open-air design, similar to night-time telescope designs, and makes thermal control of optics and telescope structure a paramount consideration. A heat stop must reject most of the energy (13 kW) at prime focus without introducing internal seeing. To achieve diffraction-limited observations at visible and infrared wavelengths, ATST will have a high order (order 1000 DoF) adaptive optics system using solar granulation as the wavefront sensing target. Coronal observations require occulting in prime focus, a Lyot stop and contamination control of the primary. An initial set of instruments will be designed as integral part of the telescope. First telescope design and instrument concepts will be presented.
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