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Large sputter coater for Telescopic mirror coating

Large sputter coater for Telescopic mirror coating

The mirrors of optical telescopes are gets damaged and tarnished over time due to oxidation, dust , impact of charged particles from space etc. Therefore, the mirror has to be re-coated from time to time to maintain the accuracy of observations. Till recently, the ability to design and make such complex re-coating equipment for large mirrors was limited to a few specialized companies in the world. Now, the Bangalore-based HHV, India’s leading vacuum technology company, has joined this select band by successfully designing and making a re-coating machine for the 360 – cm telescope to be installed at Devasthal, 60 kms away from Nainitaland is Situated at an altitude of 2500 meters above Mean Sea Level. The Aryabhatta Research Institute of Observational Sciences (ARIES) is setting up this facility.

HHV’s re-coater will be positioning the 370 cm dia., 4.5 tonne weight primary mirror during the coating process on a special support called the Whiffletreearrangement. This rotary work holder is fabricated from stainless steel and basically comprises a central hub attached to a thick hollow tube. Arms fromthis central hub lead to three 9-point kinematic supports with soft pads on which the mirror will rest during the re-coating process. The location of these supports is critical since they have to take the weight of the mirror, which is 4.5 tonnes , while it is being rotated at around 3 to 5 RPM during the coating process . The thickness of the mirror is just 12 cm. Therefore, any small misplacement of the support will result in the mirror cracking. The mathematical technique of Finite Analysis is used to determine the optimal position of the supports. To top it all, ARIES has been supplied the system by HHV at half the price quoted by a German company which is one of the leading global vendors of such machines.

This is not the first time HHV has made and supplied coaters for telescope mirrors to Indian users. It has supplied one to IUCAA, Pune for its 2.2 metre telescope which is installed at a height of 14,700 feet above MSL and another unit to the Indian Institute of Astrophysics, Bangalore, for its 2 metre telescope.