Keeping an eye on the stars

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April 2004 Motion Control & Drives

The Southern African Large Telescope (SALT) project near Sutherland in the northern Cape, will be able to retain its focal point while the earth rotates, thanks to a Rexroth STAR linear motion system supplied by Tectra Automation, and installed by Reutech Radar Systems - the designers of this innovative solution.

Including the bearing and ball screws for SALT's tracker system, the specialised linear motion solution from Tectra plays an important role in the operation of the telescope's tracker. The six-degrees-of-freedom motion system revolves around an X-Y philosophy, whereby two X-support rails are mounted on the upper and lower beams of the Top Hex structure. Two separate Rexroth ball screw assemblies drive the carriages on these rails.

The 11 m long tracker beam is mounted on two carriages, which travel on Rexroth ball rail linear guides and driven up and down by a single ball screw assembly

The 11 m long tracker beam is mounted on these two carriages, with the top surface of the tracker beam at an angle of 37° to the horizon. Carrying the optical payload, a Hexapod carriage travels on Rexroth ball rail linear guides along this beam, and is driven up and down by a single Rexroth ball screw assembly.

This technology has significantly reduced the capital expenditure required to erect the telescope. A conventional telescope tracks the apparent motion of a star image by moving its massive primary mirror and support structure precisely in unison with the target image. For very large telescopes like SALT, maintaining the mirror's exact shape while tilting it to point at astronomical objects becomes technically challenging and expensive. In addition, the drive system to move such a large mass precisely over large, angular extents is also expensive to design and build. In contrast, the design of SALT allows the primary mirror to be stationary during an observation, and always with the same orientation with respect to gravity. This feature simplifies the mirror support problem and significantly reduces the total cost of the telescope.

For more information contact Kevin Lombard, divisional manager, linear and assembly technologies, Tectra Automation, 011 971 9400, [email protected], www.tectra.co.za

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Motion Control & Drives

Keeping an eye on the stars

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