20 Mar 2017

One of the joys of working on TMT is the opportunity to collaborate with and learn from amazing people all over the world, including Japan. International flights to Osaka land at Kansai airport, which was built on an artificial island during the 1980s and 1990s. Final approach against the dramatic backdrop of ocean, rivers and hills is breathtaking, and looking out at the fragile glory of our planet beneath us is invigorating after flying thousands of miles across the Pacific Ocean. Osaka Prefecture is where one of TMT’s most complex and expensive subsystems, the Telescope Structure, is being designed and built by Japanese engineers.

The design has already taken decades of work. The TMT Project Office first prepared a Design Requirements Document laying out what the Telescope Structure has to be able to do. The Structure needs to provide mounting for the telescope optics, adaptive optics systems and the astronomical science instruments, and maintain their alignment under operational conditions. The primary mirror alone will have a mass of 144 metric tons, as much as two entire bullet trains, giving a sense of just how much mass has to be supported by this Structure. Change in alignment due to gravity acting on the Structure has to be looked at carefully, especially given that the direction and amount of that deformation depends on where the telescope as a whole is pointing.

The Structure also has to provide precise motion control for pointing, tracking and guiding, and efficient slewing from one astronomical object to the next. The Structure needs to provide distribution infrastructure such as cable wraps, cable trays and attachment points for the utilities and services (including power, coolant, cryogen, compressed air, and data and communication lines) required to perform astronomical observations. The Structure must be able to adapt to varying environmental conditions, including the effects of gravity, weather, and other internal and external factors. And of course the Structure’s design also has to provide safe and ready access for the people who will use, maintain, calibrate, and repair it.

The National Astronomical Observatory of Japan has contracted with Mitsubishi Electric in Osaka to finalize the design, and to build the telescope structure in accordance with those requirements. Mitsubishi has a track record of building antennae not just for the industrial and military sectors, but also for astronomy. For example, Mitsubishi designed and built several of the telescopes for the Atacama Large Millimeter/submillimeter Array in Chile, where I worked before joining TMT.

Mitsubishi Electric took the conceptual design of the telescope structure and refined it to preliminary design level and now final design level. Here’s a computer aided design (CAD) model of Mitsubishi’s updated design. The primary mirror segments are shown here in cyan, along with the main structural tubes (grey and brown). The platforms on either side (turquoise) house the instruments (blue) for the adaptive optics and the science observations.

[Image]
(A) Image Title: Mitsubishi’s Updated Design of the Telescope Structure
Image Caption: View of Thirty Meter Telescope, showing Primary Mirror Segments.
(B) Image Title: Another Perspective of the Telescope Structure
Image Caption: View of Thirty Meter Telescope, showing Mirror Cell Assembly underneath Primary Mirror.