Suppliers bring Swiss precision to large telescopes

Let there be light. Starlight, precisely. At 4,415 metres above the Pacific Ocean, on the summit of the Mauna Kea, the highest volcano on Hawaii’s main island, the new MOSFIRE instrument at the Keck observatory will receive its first light from distant stars in May 2011. Captured by one of the gigantic 10-metre-diameter telescopes of this twin observatory, the light will then travel through a high-precision configurable slit mask to focus on specific objects such as young stars or galactic centres. The mask is part of a larger instrument, the 2.2-tonne MOSFIRE (Multi-Object Spectrometer for Infra-Red Exploration), designed by Caltech and UCLA to observe distant stars. It is used to select 46 celestial objects and to block unwanted light.

Weighing 45 kilograms and 1.20 metres long, the configurable slit mask, developed by Peter Spanoudakis and his colleagues at the CSEM since 2005, contains 92 aluminium bars, 46 on each side. The bars are engaged by sapphire teeth and displaced by custom actuators to create the shadowing mask needed for a specific observation. To be efficient, the trick is that this big mechanism has to have a precision of one micrometre, and it has to function under the cryogenic conditions within MOSFIRE. “That means the system has to be entirely programmable from the outside,” explains Spanoudakis. “Also, reliability is key.” With one night of observation at Keck costing around 100,000 dollars, any repair would be extremely expensive. Tested at CERN

To meet those challenges, the CSEM Systems Division in charge of building this mask had to dig for special competencies throughout Western Switzerland’s cluster of microtechnology subcontractors. About 20 suppliers teamed up behind the CSEM flag to achieve the precision mechanics needed to build the device. Among them, Arcofil, a specialist in electroerosion, manufactured the large parts. Borotec was in charge of the aluminium bars. Reymond & Co made the sapphire teeth. Mercatex, in Losone in the canton of Ticino, made the flexure elements for the actuators that move the bars, while MPS integrated the subassemblies. Assembled in CSEM’s clean room, the device was then tested at –150 °C at the European Organisation for Nuclear Research (CERN) in Geneva before it was shipped to the United States.

The knowhow acquired during that project is planned to be used in similar instruments for the next generation of very large telescopes. The decision has already been taken for the Thirty Meter Telescope which is currently on the drawing board and will be constructed in Hawaii near the Keck Telescopes.

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