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From tiny flex pivots to extra-solar gas giants

30 April 2020

Katherine (Katie) Morris is a mechanical engineer on STFC’s graduate programme, at the UK Astronomy Technology Centre (UK ATC) in Edinburgh. Here she is pictured, working on the ‘immersed echelle rotation mechanism’ for METIS – a new ground-breaking instrument for leading-edge astronomy research.

In Greek mythology, Metis was the spouse of Zeus and mother of Athena, goddess of wisdom. Today, to astronomers, METIS stands for the Mid-infrared ELT Imager and Spectrograph. It will be one of a suite of first-light instruments for the Extremely Large Telescope, or ELT. The ELT is currently in construction for the European Southern Observatory (ESO) at the Paranal Observatory in Northern Chile.

Expected to be operational in the late 2020s, the ELT will be the largest visible and infrared telescope ever built. It will have a 39-metre primary mirror that will gather 217 times more light than the Hubble space telescope. At 80m high, it will stand taller than a football stadium (or because we’re in Scotland, taller than the Scott Monument on Edinburgh’s Princes Street).

As well as its imposing size, the ELT will be much more powerful than any other telescope. If it was placed at Land’s End, it could see a bumblebee at John O'Groats (or a Highland cow on the Moon). At these dimensions and this much observing power, it is certainly aiming to live up to its moniker – the ‘Biggest Eye on the Sky’!

“My job,” says Katie, “is to develop and test the mechanisms that will rotate the optical components inside the METIS instrument, for the ELT. The mechanisms need to be extremely accurate and repeatable, and work at around -200 degrees C.

“Specifically, I’m working on the LM-band high resolution Spectrometer (the LMS). LM describes a particular section of the electromagnetic spectrum; which is light emitted in the near infrared at 3-5 microns, and the spectrometer part is what enables scientists and astronomers to analyse that light.

“The METIS-LMS will be a powerful component of the instrument – enabling astronomers to study in detail the atmospheres of nearby extra-solar gas giants. What’s really exciting is that as a mechanical engineer, I must take the science requirements for the instrument and turn them into mechanical requirements that will deliver to the science goals.

“On the rotating mount development for the L-M band spectrometer, I work with the tiniest of flex pivots to build the capability for METIS to answer some of astronomy’s biggest questions. 

“What is particularly unique about the mechanical engineering requirement for this part of METIS – is that the rotating mount must rotate the echelle with a positional accuracy of a few ten thousandths of a degree –that kind of ‘fine repeatability’ is exceptionally challenging to achieve in a cryogenic instrument.

“I model the mechanics of the various components of the rotating mount with computer-aided design (CAD) software tools. It’s quite nerve wracking when the physical piece is then made – based on my design and calculations.

“In engineering we talk about ‘tolerance’ – no machine can exactly manufacture to the dimensions set – and so we build in tolerances – a permissible limit in variation on the design. Sometimes, when ‘bits’ get made, they don’t always fit and work together as they should – and then it’s back to the drawing board to think of another way or to make modifications to the design. When it all works, there really is nothing more satisfying than the feeling of “I thought of this – and now it’s made.”

On what’s next for the design of METIS, Katie continues:

“The next stage in the development of the rotating mount is to ensure that “off-the-shelf” parts from external suppliers perform as expected. Based on the specifications given by the manufacturer, I selected a piezo linear drive as the actuator (a component that will move and control the mechanism). I must now test the assembly to make sure it achieves the very small repeatability required.

“After the mechanism concept has been verified through testing, I will go ahead with manufacturing parts to the geometry that is more representative of the final METIS instrument. I must also consider how to mount the optical parts within the mechanism. At first we will use a dummy optic; this allows us to ensure the suitability of the mounts and handling procedures before integrating the very expensive and fragile echelle grating (a type of diffraction grating) into the instrument.

Of working from home during the COVID-19 response, Katie concludes:

“Working from home has meant that my mechanism testing has been paused. However, there is still a lot of design work that we can do; I am redesigning some of the mechanism geometry to incorporate parts from external suppliers that will be delivered after the lockdown is lifted. I am expecting to receive a cryogenic rotary encoder from a company in the USA and it will save a lot of time if I have prepared a design that can be manufactured for when it arrives.

“Although we have had to adapt the type of work that can be done during the COVID-19 response, the design work continues, and the METIS team at UK ATC are still having our weekly meetings and we are also in touch with the METIS Project Office and receive regular updates about the progress of our consortium partners.”

METIS is being built by a consortium of European institutes, led by Leiden University in the Netherlands.  STFC’s UK Astronomy Technology Centre (UK ATC), where Katie is based is responsible for the spectrometer whose primary science targets include exo-planets – planets that orbit around stars outside our solar system.

For more information:

About METIS/ELT:

The UK Astronomy Technology Centre (UK ATC):

Based at the Royal Observatory in Edinburgh and operated by the UK’s Science and Technology Facilities Council (STFC) and part of UK Research and Innovation (UKRI), the UK Astronomy Technology Centre (UK ATC) is the national centre for astronomical technology. The UK ATC designs and builds instruments for many of the world’s major telescopes on land and in space. It also project manages UK and international collaborations and its scientists carry out observational and theoretical research into questions such as the origins of planets and galaxies. @ukatc

Science and Technology Facilities Council (STFC):

The Science and Technology Facilities Council is part of UK Research and Innovation – the UK body which works in partnership with universities, research organisations, businesses, charities, and government to create the best possible environment for research and innovation to flourish. STFC funds and supports research in particle and nuclear physics, astronomy, gravitational research and astrophysics, and space science and also operates a network of five national laboratories as well as supporting UK research at a number of international research facilities including CERN, FERMILAB, the ESO telescopes in Chile and many more. Visit stfc.ukri.org for more information. @STFC_Matters

UK Research and Innovation (UKRI):

UK Research and Innovation works in partnership with universities, research organisations, businesses, charities, and government to create the best possible environment for research and innovation to flourish. We aim to maximise the contribution of each of our component parts, working individually and collectively. We work with our many partners to benefit everyone through knowledge, talent and ideas.

Operating across the whole of the UK with a combined budget of more than £7 billion, UK Research and Innovation brings together the seven research councils, Innovate UK and Research England. @UKRI_News

European Southern Observatory (ESO):

ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world's most productive astronomical observatory. ESO provides state-of-the-art research facilities to astronomers and is supported by Austria, Belgium, the Czech Republic, Denmark, Finland, France, Germany, Ireland, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom, along with the host state of Chile. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising co-operation in astronomical research. It operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. @ESO


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Last updated: 30 April 2020

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