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《美国三十米望远镜圆顶准备制造》

  • 来源专题：天文仪器与技术信息
  • 编译者： zwg@niaot.ac.cn
  • 发布时间：2020-06-12

  • Pasadena, CA – TMT’s Enclosure System has achieved its final design milestone, successfully passing a series of Production Readiness Reviews (PRR) in March 2020.

    Over the last several years, the enclosure design has progressed through its final design phase followed by the completion of the models, drawings and specifications required for procurement and fabrication. Completion of the PRR sets the stage for effectively starting the procurement and fabrication of the enclosure parts, which will be followed by factory assembly, testing, and shipment of the enclosure components to the TMT construction site.

    The TMT Enclosure calotte design, selected after extensive trade studies, is a spherically shaped building that surrounds and protects the telescope and instrumentation during non-observing time and in severe weather conditions. During science operations, the enclosure aperture opens to allow the telescope a clear and unobstructed view of the sky.

    Fundamental features of this calotte design include:

    A minimum size due to its spherical form. The clearance between the inside of the enclosure and some telescope parts is as small as 0.5 meters in some places.

    A minimum aperture opening that provides maximum protection to the telescope from windshake, critical for maximizing telescope image quality performance.

    A very low mass for a structure of its size due to the structurally-efficient calotte shape. The enclosure can be repositioned to any point in the sky very quickly with reasonable drive power demands.

    The TMT enclosure has been designed to minimize its mass and size, with enhanced control and performances during scientific observations. This unique design will enable rapid changes of pointing direction, while providing a maximum protection from wind-induced vibrations and dome-seeing degradation, which could otherwise impact the performances and image quality of the telescope.

    “TMT’s enclosure is unique among the Extremely Large Telescopes being built today,” says Luc Simard, Director General of the Herzberg Astronomy and Astrophysics Research Centre. “It will facilitate the observations of astronomical phenomena requiring a rapid response and will deliver optimal conditions for Adaptive Optics observations at an unprecedented spatial resolution. TMT's enclosure design will be key to the scientific success of TMT.”

    The PRR focused primarily on the structural and mechanical fabrication drawings, electrical schematics, specifications, and special processes for fabrication of TMT enclosure components and assemblies. However, additional independent assessments of compliance to the enclosure design requirements, management, safety and risk were also completed as a part of the review. The review board unanimously agreed that the fabrication data package for the enclosure structural, mechanical, electrical and control systems is now complete and ready for the enclosure fabrication phase.

    TMT’s enclosure design was completed by Empire Dynamic Structures of Port Coquitlam, BC, Canada as a Canadian in-kind contribution to the TMT Project, managed by the Canadian National Research Council (NRC). The work was conducted through a contract between Dynamic Structures and the Canadian Commercial Corporation (CCC) on behalf of the NRC. Dynamic Structures assembled an excellent and dedicated team of structural, mechanical, electrical, systems, controls and CAD engineers to complete the work.

    TMT Enclosure Design Overview

    The TMT calotte style enclosure consists of 3 major structural components; the base, cap and shutter. The base is the lower portion of the enclosure and it rotates about the azimuth axis. The cap and shutter upper sections rotate in a plane tilted 32.5 degrees from horizon. Through combined motion of the base, cap and shutter, the shutter aperture can be positioned anywhere within the viewing range of the telescope.

    Relative motion of the cap and shutter is used to either close and seal the enclosure or open the shutter aperture during science observations. The shutter structure is located directly inside the cap structure. It consists of an open steel framework supporting a steel plug structure. The shutter rotates about 180° around the same axis as the cap, enabling opening and closing of the telescope aperture. The cap also includes a set of deployable external flaps designed to divert incoming air flow and provide wind protection for TMT secondary mirror.

    There are a total of 88 inner and outer ventilation doors which are used to provide controlled ventilation of the enclosure during astronomical observations. These vents can be opened or closed to modulate the amount of outside ambient air flowing through the enclosure and maintain a steady flow and air temperature within the optical path. Calculations using Computational Fluid Dynamics modeling have shown good wind flushing properties inside the TMT dome and around the telescope to eliminate thermal effects on the seeing.

    The telescope enclosure, which is 66 meters in diameter (about the width of a soccer field), has a height of approximately 56 meters above the surrounding ground and a total mass of 2900 metric tons. It is able to open its 31.25 meter diameter aperture in less than 2 minutes and will allow the telescope to point an astronomical object in under 3 minutes.

    The enclosure is equipped with 3 crane systems to facilitate the maintenance and technical operations of the telescope and instrumentation systems. The enclosure safety requirements are fully defined and provide adequate safety for the observatory personnel and visitors, including local emergency stop buttons, sensors and wiring that interface with the observatory safety system.

  • 原文来源：https://www.tmt.org/news/461
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  • 《美国三十米望远镜TMT圆顶最后设计将完成》
    • 来源专题：天文仪器与技术信息
    • 编译者：zwg@niaot.ac.cn
    • 发布时间：2017-08-23
    • As I write this, the final design for TMT’s enclosure—a huge, moveable dome that will house the telescope—is nearing completion. A substantial portion of the final design has already been done, allowing for work to begin on the production readiness phase. The last of the design reviews, for the enclosure’s electrical and controls aspects, is planned for the coming months, with the hope that a contract for the fabrication phase and making all the parts can be signed in the new year. Here’s a fly-through animation showing the elegant design and motion of the enclosure: http://www.tmt.org/gallery/video/aluminized-dome-motion. As you can see from the video, TMT is like a great eye—one that will let us see into the far distance and the far reaches of time, where we will make discoveries and maybe even finally find signs of life beyond our own. You can think of TMT’s primary mirror as the lens and retina of the eye: the parts that let us focus on and resolve images. 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Smooth and Strong – A Complex System It may be surprising to learn how complex the enclosure is, and how many factors we have to consider in creating it. The enclosure dome will be 56 meters high and 66 meters across. The dome’s design is called a calotte (cap), and, as shown in the video, that description fits well. The enclosure consists of four basic components: a fixed base, and above that, a rotating base, rotating shutter, and rotating calotte. Here’s a diagram showing these subsystems: TMT Enclosure Exploded View As you might imagine, the fixed base has to be strong enough to support the rest of the enclosure. And as the diagram shows, the fixed base and rotating base fit together along a horizontal plane, which is partway above the observatory floor. Still further up, the connection between the moving base and the calotte structure is tilted, and within the calotte is the aperture opening. Here’s cross-section showing how the telescope itself rests safely within the enclosure: Cross Sectional View of TMT Enclosure Once the telescope is assembled and operational, it will work in concert with the moving enclosure. To make observations, we first move the shutter to open up the aperture, then we move the calotte and rotating base relative to each other and to the fixed base, thereby shifting the aperture up, down and sideways as needed, as depicted in the video clip at the beginning of this article. In the video, the enclosure’s movement is smooth and seems easy, but of course achieving that movement is a complicated, multifaceted undertaking, and as with all complex scientific and technical endeavors, we need to be clear on what every subsystem must be able to do in order to achieve the necessary overall scientific performance. In system engineering parlance, we say each subsystem has to meet its technical requirements. TMT’s enclosure is no exception. The requirements are compiled in a Design Requirements Document, and each requirement is uniquely numbered. For example, Requirement [REQ-2-ENC-0870] addresses the enclosure’s tracking motion, and specifies: “The enclosure system shall be capable of tracking the position of the aperture opening to the virtual motion of a target on the sky over the required range of motion within a peak error of 10 arcmin in each axis on the sky.” 10 arcmin (arcminutes) is roughly a third the diameter of a full Moon, as seen with the unaided eye from Earth. This enclosure tracking is less precise than that required by the telescope itself, but is still a significant challenge, considering the size and weight of the enclosure, and the additional requirements of moving smoothly at very slow speed. We need the motion to be smooth because we don’t want to transmit vibrations to the telescope and cause image jitter. Earthquakes and Temperature Variations Another specification the telescope enclosure must meet deals with earthquakes. Our choice of location for the observatory means we’re somewhat vulnerable to earthquakes, and so when designing the enclosure we have to plan for them. Our specifications mandate that the enclosure be able to ride out “frequent earthquakes” (earthquakes that might occur every 10 years or so) with no damage: normal observatory operations staff should be able to ensure that operations can resume almost immediately after such an earthquake. After an “infrequent earthquake”—one expected to occur only once every 200 years—the enclosure needs to be able to resume operations within two weeks using spares that are on-site, normal operations support staff, and normally available equipment, though this work may include replacing one-time consumable items. Finally, we need to anticipate a “very infrequent earthquake,” the kind expected to occur only once every 1,000 years. The design requirements state that no permanent deformation resulting from this magnitude of earthquake shall prevent closing and sealing of the enclosure. Both the structural and mechanical systems must be robustly designed to enable shutter closure after a major earthquake event. This functionality allows the enclosure to fulfill a critical design requirement: to protect the telescope from damage. As important as the enclosure’s movement and sturdiness are, those things are still not enough. A number of other considerations influence the enclosure’s design. One of the most important is temperature. Much like us, TMT is highly sensitive to temperature, both inside and outside. When we have a fever, or if it’s too hot or cold for our comfort, we don’t feel or function our best. TMT’s sensitivity to temperature, too, affects how well it functions. Inside TMT’s enclosure, temperature differences in the air can cause turbulence. 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  • 《美国三十米望远镜主镜计量框架已制造完毕》
    • 来源专题：天文仪器与技术信息
    • 编译者：zwg@niaot.ac.cn
    • 发布时间：2020-06-12
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