By Jeff Hudson, TMT Assistant Project Manager
Engineers in California and Canada are accelerating the pace of design work on the Thirty Meter Telescope (TMT) enclosure as we count down to design completion this fall. Site specific weather and construction conditions on Mauna Kea are being incorporated. Dynamic Structures Ltd., TMT’s partner in engineering and fabrication, is analyzing the latest seismic and design choices for optimization.
The enclosure will be the first item to be built on Mauna Kea and sets the critical path for all subsequent construction and commissioning. With that in mind, on-time completion of the design package puts TMT one step closer to first light.
The scale and design of the enclosure is impressive. The enclosed floor upon which the telescope structure will be mounted is larger than 10 tennis courts; the entire structure will weigh more than 2,000 tons.
The enclosure is unique in large telescopes because it utilizes a “callotte” design, whereby the shell rotates in two planes allowing the aperture to be perfectly located over the telescope. This design is the most efficient shape, reducing both size and weight, which is reflected in the enclosure’s drive size and power requirements. Along with an efficient overall shape, the calotte design reduces the size of the opening, thereby minimizing wind buffeting of the telescope’s top end. But like all design decisions, a reduced opening presents a few drawbacks that need to be addressed in other ways. By reducing wind buffeting, the opening also reduces the amount of air moving over the primary mirror. And, as it turns out, a small amount of air is a good thing. To compensate for this, the dome will have 94 vents, each with an outer door and an insulated inner door. The vents can be selectively opened to allow optimum air flow over the primary mirror surface.
Now that we have the structure defined, we have to get it to work and survive. TMT’s environmental requirements ensure that the telescope will survive some of the harshest conditions on the planet. Made to operate in constant freezing temperatures, survive earthquakes, and take a beating from 180 mile-per-hour winds, the enclosure must be both structurally strong and scientifically optimized. All of this is achieved through thousands of hours of analysis and prototype design. And just when you think you’re done, you have to find a way to transport it, piece by piece, to a remote summit. The construction planning and erection sequencing is as complicated for the engineers as any of the design elements. But when it’s done, the world’s first next-generation telescope will have a home that is both functional and beautiful in its design.