Hydrostatic Bearings and Precision Machining Aid Performance of World’s Largest Telescope

An international consortium of 16 universities and research institutions is in the process of building the Giant Magellan Telescope, considered to be the largest Gregorian optical infrared telescope ever engineered. Up to 200 times more powerful than existing telescopes, it will enable scientists around the world to see farther into space than ever before.

Production for many parts of the telescope is underway, including its mount which utilizes hydrostatic bearings for accurate and frictionless movement. Precision machining of the mount and its components will help ensure the Giant Magellan Telescope is able to move with the smoothness and accuracy of a laboratory instrument.

Why Hydrostatic Bearings Were Chosen for the Giant Magellan Telescope

Two hydrostatic bearings are incorporated into the telescope structure to support the azimuth (vertical) and elevation (horizontal) axes explained Keath Beifus, Senior Mechanical Engineer, Telescope Structures, Giant Magellan Telescope, during a virtual event discussing progress of the telescope project.

The less friction created, the better because it can lead to heat buildup and wear, both of which could negatively impact performance of the telescope and lead to maintenance issues. Given the large size of the telescope and its components, there are not likely to be off-the-shelf replacement parts at the ready should an issue occur. Therefore, it is critical to utilize technologies designed for reliability so potential downtime can be minimized as much as possible.

High stiffness — a bearing’s ability to maintain its shape while supporting a load — was another reason Beifus said hydrostatic bearings were chosen for the telescope. “The hydrostatic bearings provide excellent stiffness, both statically and dynamically, which enables extremely accurate pointing and stable tracking of celestial targets under normal operating conditions.”

The final reason he noted for choosing hydrostatic bearings was the fact they could be integrated with an earthquake damping system. “The same hydraulic system that provides oil to the bearings is also used to mitigate seismic damage to the telescope,” said Beifus. “This system provides vertical isolation and damping to the rotating telescope structure.”

The complete telescope mount, including its use of the hydrostatic bearings, was designed by OHB Digital Connect GmbH.

High Level of Precision Required to Manufacture the World’s Largest Telescope

Ingersoll Machine Tools, part of Camozzi Group, is producing the mount that will support and move the Giant Magellan Telescope’s seven primary mirrors, instruments and control systems at its facility in Rockford, IL. The company was chosen for the project due in part to its years of experience in building large structures and machines including submarines, spacecraft and satellite structures.

Kimberly said the Giant Magellan Telescope project “has grown into one of the most ambitious engineering and machining projects we've ever undertaken.” He said the mount stands 39 m tall and weighs 2,600 tons.

“The telescope is so large that we had to build a new 40,000 sq. ft. manufacturing and assembly bay, including a giant pit just to machine and assemble it,” said Kimberly.

The Ingersoll Machine Tools facility also has the largest five axis master mill gantry machine in North America. It is currently being used to set up the first three semi-finished azimuth tracks that will be finish machined with key features including the hydrostatic guideways. The azimuth track enables a full 360-degree rotation on the x-axis and 25 to 165 degrees on the y-axis.

“Each of these enormous tracks weigh over 50,000 lbs. and presents a challenge at every step of the manufacturing process,” said Kimberly. “The fabrications themselves had to be flat within 13 mm from end to end; that's just over a half inch.

“When machining the azimuth tracks, we’ll be holding a flatness to within two thousandths of an inch in the zone where the hydrostatic pads ride, and within 12 thousandths of an inch over the entire 70 ft. diameter when the tracks are assembled.”