Critical elements of one of the world’s largest telescopes are guided and protected by extruded aluminium profiling from Bosch Rexroth.
The profiling, which is used for rapidly constructing structures and building safety constructions, has been employed to solve some challenging problems on the large binocular telescope (LBT) located on Arizona’s Mount Graham, USA.
As tall as an 11-storey building, the LBT’s viewing power exceeds that of the Hubble telescope by a factor of 10, allowing scientists to peer into the depths of the universe. However, structural engineering also plays a vital supporting role at the facility.
It is the optical elements that make the LBT so fascinating – the LBT is the only such telescope in the world that uses two mirrors on a common platform. Each mirror is 8,4 m in diameter. The mirrors are linked optically, and attain a resolution corresponding to that of a 22,5 m mirror. Located about 24 m below the mirrors is the PEPSI (Potsdam Echelle Polarimetric and Spectroscopic Instrument), a high-resolution spectrograph built by the Astrophysical Institute of Potsdam (AIP) in Germany. The light gathered by the mirrors has to be continuously fed to PEPSI.
The light passes through high-sensitivity fibre-optic waveguides which are bundled inside jackets to form the 'energy chain'. One of the greatest challenges involved with the LBT project has been to stabilise the energy chains so that each energy chain can move on both the horizontal and vertical plane to follow the mirrors’ motion without this having any effect on the light feed.
A second challenge resulted from the fact that the PEPSI is located at the lowest point in the azimuth pit. This space is actually a large concrete cylinder with a centre that corresponds to the telescope’s vertical axis. The fibre-optics needed to be routed down through a small opening, to the spectrograph and the azimuth pit needed to be covered to prevent accidents.
Framing a solution
“We knew how to approach the problem,” explains Frank Dionies, mechanical engineer, AIP, “We use extruded aluminium made by Rexroth in a lot of our project applications.”
In order to solve the problem with the energy chain, the engineering team developed a modular framing system, in which the cable track holding the waveguide was mounted on extruded aluminium beams.
According to Dionies, Rexroth profiling and its accompanying versatile connectors allow any structure to be assembled quickly and efficiently. “After we had installed the framing, the telescope crew decided to lay one of the permanent ladders above the azimuth pit. This meant that we had to move the energy chain to the opposite side. It took only three hours to dismantle the framing, reconfigure and reassemble it, and mount it again.”
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