FEATURE EUROPEAN EXTREMELY LARGE TELESCOPE
Reaching for the stars
The first optical components for the European Extremely Large Telescope have been approved by the European Southern Observatory. Jessica Rowbury finds out that developing the technology to make the mirror segments will ultimately strengthen the European optics industry
A
t the UK’s Photonex conference in October, David Walker, Professor of Optics at Glyndwr University in Wales, announced that the
European Southern Observatory (ESO) had approved the first components of a telescope whose construction will bolster the European optics industry – and, ultimately, transform our perception of the universe. With construction of the European Extremely
Large Telescope (E-ELT) due to begin next year, the ESO explicitly sees this project – the largest optical infrared telescope in the world – not only as a boost to science but also to European technological capacity. According to Marc Cayrel, project manager for the E-ELT optics at ESO: ‘We will use European industries to manufacture the optics used in the E-ELT. Making a telescope is not only to help science, but to reinforce our industry within Europe. Building the E-ELT is an opportunity to strengthen the European optics industry.’ The UK’s National Facility for Ultra Precision Surfaces, operated by Glyndwr University in partnership with University College London and precision polishing company Zeeko, has been responsible for manufacturing prototype mirror segments for the E-ELT. Walker told the Photonex conference, in Coventry, UK: ‘The acceptance tests have been conducted on the first segment and we received the formal certificate of acceptance from ESO on the 15th October.’ The primary mirror, measuring 39 metres,
16 ELECTRO OPTICS l NOVEMBER 2013
will be segmented because it is not feasible to build such a large mirror in one piece. As Walker, who is also professorial research associate of University College London and research director at Zeeko, says: ‘You would not try to buy one enormous tile to go on your bathroom wall; you would buy a box of tiles and put them on the wall. It is exactly the same; these very big telescopes are always segmented.’ The next stage will be to produce the segments on a larger scale. ESO’s design of the E-ELT is now well-advanced, and the preliminary specifications for the optics are available. The tender for the primary mirror segments is anticipated for 2014/15, and the two main organisations in Europe that can fabricate these optics are Sagem in France and the UK’s National Facility. However, it is implausible that a university would be given a contract for mass-production of the segments – so segment manufacture, or process-stages, might be split between vendors. Walker says: ‘After finishing the prototype, we are currently in the process of investigating partnerships with optics fabricators, under which a partner company would take on the technology and establish a new manufacturing facility.’ The E-ELT is due for completion in 2022 and it will take six years to manufacture the optics. The telescope will need 931 segments, including the spares, and Walker explains that the industry would struggle to produce such optics at a rate of about three per week: ‘If I go out to tender today for just one of those
Artist’s impression of the European Extremely Large Telescope (E-ELT)
segments, I would probably be quoted 15 months’ delivery time.’ Moreover, he remarks: ‘Look at the worldwide experience of delivery- time of large optics, and the history of damage to surfaces in manufacture.’ To then scale up to the E-ELT, which has nearly 1,000 segments that have larger and more complex surfaces, creates a significant challenge. ‘You see that this classical approach to manufacture is no longer appropriate,’ says Walker. ‘In other words we need a whole new way of thinking about optical manufacture.’
Automation and mass production technologies need to be brought to optics. Walker comments: ‘When working with such parts, 0.5m and upwards, there tend to be bespoke processes and manual interventions.
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