Bearings guide giant optical telescope

The largest optical telescope in the Southern Hemisphere is using air bearings and a rotary table bearing to help it remain in one position rather than having to compensate for the earth's rotation. Dean Palmer reports Rotary table bearings are playing an integral part in helping scientists gaze at the stars on the largest optical telescope in the Southern Hemisphere. The design features allow the telescope, which is located at 1,800 metres above sea level, to remain in one position rather than having to compensate for the earth's rotation. There is no need for operators to move the telescope at all during observation in order to compensate for rotation of the earth and the mirror is installed at a fixed inclination angle of around 37 degrees to the zenith. The telescope's 11-metre diameter reflector unit consists of 91 hexagonal, aluminium-coated mirrors that can be individually aligned. The entire reflector unit is supported by air bearings and guided by INA FAG's YRTM 395 rotary table bearing. With a restricted axial and radial run out of 3µm and an encoder measurement accuracy of ±3 angular seconds, it precisely fulfils the required accuracy. INA also designed six custom telescopic struts and supplied cardanic joints to support the 4.5-tonne telescopic tracker, which receives the bundled signal. The tracker can be precisely positioned to 6µm. A support roller combination, which includes 58 INA type NUKR 40 stud type track rollers, guides the rotating cupola. The South African Large Telescope (SALT) is located in the Karoo Desert, South Africa and will give its operators a glimpse into the history of the universe at a cost of 30 million US dollars. The telescope will be used to collect the light that was emitted by stars and galaxies almost 14 million years ago. According to Andreas Pieper, head of technical market development for Asia, South Africa and Australia at INA, the telescope is a billion times more powerful than the human eye. "The telescope can, in principle, detect the light of a burning candle on the moon," he stated. "The SALT operators have reported to us that our bearings have passed all their tests and are running to complete satisfaction." The US is considering the construction of eight similar telescopes.