Canadian Consulting Engineer

The Gemini Project

December 1, 2000
By Canadian Consulting Engineer

Consulting engineer: Agra CoastA firm of consulting engineers in British Columbia is helping science investigate the vast expanses of space. Agra Coast, a specialist division of Amec (formerly Agra), ...

Consulting engineer: Agra Coast

A firm of consulting engineers in British Columbia is helping science investigate the vast expanses of space. Agra Coast, a specialist division of Amec (formerly Agra), located in Port Coquitlam, British Columbia, is one of the few firms in the world involved in designing and building astronomy telescopes and their enclosures. They are helping create the tools that enable astronomers, with increasingly accuracy, to observe objects in the universe millions of light years away. From these discoveries we hope to find answers to the biggest mysteries of all — what was the origin of our universe, and how is it all likely to end?

Agra Coast’s expertise in complex structural mechanical systems and precision-fitted curved steel structures stems with two B.C. companies it acquired in the 1970s: Coast Steel Fabricators and Brittain Steel. The latter specialized in designing astronomy telescope enclosures, and under the technical leadership of David Halliday, P.Eng., Agra Coast continues the tradition. (Halliday is also an adjunct professor in applied science at the University of British Columbia.) Halliday’s first experience with world-class observatories was with the Canada France Hawaii telescope in 1975, followed by the Sir William Herschel and Sir Isaac Newton telescopes in the Canary Islands in the 1980s. As the company gained confidence it became involved in the ambitious Keck 10 meter telescope project in 1985, for which Agra designed and built both the enclosures and the telescope for the Keck II portion.

Most recently, the engineers have been involved in the high profile Gemini project to build a pair of large telescopes in the southern and northern hemispheres. They designed and built the enclosure for Gemini North, which started operating this year alongside the cluster of other observatories atop Mauna Kea in Hawaii, 4,214 metres above sea level. They also designed and built the enclosure for its “twin,” Gemini South, which is being assembled on Cerro Pachon, 2,715 metres above sea level in the foothills of the Chilean Andes.

The Gemini telescopes are eight metre telescopes, providing 10 times the observing power of the previous four-metre generation of telescopes. They will allow scientists to observe the entire night sky for the first time — both north and south hemispheres — taking both infrared and optical readings. From the Gemini headquarters at the University of Hawaii-Hilo, astronomers will analyze the data from the telescope instruments, and search for evidence of phenomena such as the formation of planetary systems, galaxies, the origins of chemical elements, quasars and active galactic nuclei. By October this year, the Gemini North observatory had already provided unprecedented sharp images of a star being whirled through a gas and dust cloud near the black hole at the centre of the Milky Way.

The key to the superior performance of the Gemini telescopes is their 8.1-metre (27-ft) diameter, primary mirrors. As Halliday describes it: “The bigger the mirror, the further back you can see in time.” They also have a protected silver coating on the mirror (rather than aluminum), and “Adaptive Optics” which help reduce the effects of atmospheric turbulence.

Engineering the domes

For the telescopes to function at their best, it is critical that they be maintained in a stable environment. The equipment is very sensitive to heat, which can distort the view, as well as to noise, which can cause it to vibrate. The enclosures that Agra Coast designed to house the telescopes are therefore a very important component of the overall project.

The domes were made as prefabricated parts at Agra Coast’s Port Coquitlam yard, then assembled as a dome and put to various tests to ensure they will withstand the harsh thermal conditions and wind loads of up to 200 miles an hour that will buffet them on their mountaintops. The containerized pieces were then transported by sea and truck to their respective sites.

In engineering the enclosures, explains Halliday, one of the most important tasks was to create conditions around the telescope that are as close as possible to the ambient air. At these high elevations there are wild temperature fluctuations, with a lot of solar gain by day, followed by temperatures dropping as much as 20C at night. To balance the outside and inside air as quickly as possible, Halliday’s team designed the first “flushing” dome for Gemini. In this system, three-storey high vent shutters, “like two lips,” around the domes open 120 degrees at night to let the outside air enter and circulate around the telescope. The aluminum and fibreglass shutters weigh 50 tons but are counterbalanced so that the motor power required to move them (hence the vibrations) is quite small. Aluminum baffle structures in the vents help to stop the incoming wind from buffeting the telescope. Also incorporated within the enclosure are two large observation shutters that open to allow the telescope to point from horizon to zenith.

As the telescope tracks different portions of the sky, the top part of the dome enclosure moves 360 degrees in the horizontal plane with it. To make this movement as smooth as possible and minimize the vibrations it produces, Agra Coast designed special self-steering support bogies that compensate for thermal distortions in the enclosure as it rotates. The geometric relationship between the wheel tread and support springs tends to allow the bogie to track on the rail with little or no radial force.

Like the space program, Gemini is a multi-national collaboration led by the U.S. The project is costing $193 million, and is led by AURA, the Association of Universities for Research in Astronomy. This is a consortium of 29 U.S. universities and institutions including the National Science Foundation, the National Research Council of Canada and institutions from Australia, the United Kingdom, Chile, Argentina and Brazil.

The high stakes of engineering with precision on a project like this are formidable. A single night’s observation by Gemini costs around U.S. $33,000, so if the equipment does not work at its peak, there is a high price to pay. Still, to be able to play a role in such an important scientific endeavour must make all the mental pressure worthwhile. Besides, the engineers at Agra Coast seem to enjoy an adrenalin rush from time to time. The company’s other speciality is designing high-speed roller-coaster rides! –BL

Client: Association of Universities for Research in Astronomy (AURA)

Agra Coast project team leaders: Dave Halliday, P.Eng., David Lo, P.Eng., Ping Yu, P.Eng., Lillian Siu, P.Eng., Mike Gedig, P.Eng., Ken McLeod, P.Eng., George Hilderbrand, Bill Page


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