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Meet Jonathan Strachan, Senior Mechanical Engineer - He shares with us the MOONS vacuum vessel story

The MOONS vacuum vessel leaving cryogenic engineering company AS Scientific at the start of its journey to UK ATC
The MOONS vacuum vessel leaving cryogenic engineering company AS Scientific at the start of its journey to UK ATC
(Credit: STFC)

14 February 2020

“We think MOONS has the biggest vacuum vessel in astronomy. Do you know of a bigger one?” ask scientists and engineers at the Science and Technology Facilities Council’s (STFC’s) UK Astronomy Technology centre (UK ATC) in Edinburgh.

This whopping vacuum vessel weighs in at over 3,000kg and is almost 4m high by over 2.5m wide. It has been built for MOONS – which stands for Multi-Object Optical and Near-infrared Spectrograph.

MOONS is a new ground-breaking astronomical instrument that will be operational in 2021 on the European Southern Observatory’s (ESO) Very Large Telescope (VLT) at the Paranal Observatory in Northern Chile.

The VLT is one of the world’s most advanced telescopes and MOONS will enable it to see, in unprecedented detail, the innermost regions of our

Galaxy – the Milky Way, as well as over vast distances – so astronomers can study the formation and evolution of galaxies over the entire history of the Universe.

MOONS is a unique astronomical instrument which is being designed, built and assembled at UK ATC in collaboration with an international consortium of institutions and commercial partners. We catch up with Jonathan Strachan, Senior Mechanical Engineer – responsible for the design and assembly of the spectrograph – which will sit inside the vacuum vessel!

Hi Jonathan. Great to talk to you. WOW that certainly is a huge vacuum vessel. What happens inside it?

“MOONS effectively comes in two halves. There’s the front end, which is the bit that will bolt on to the telescope – the VLT, in Chile. That’s where all of the optical fibres sit – 1,000 of them! – that align with and collect the light, from astronomical objects in the sky. Those 1,000 fibres then come off in a big bundle and feed their way back into the part of the instrument that I’m responsible for – the spectrograph.

“MOONS has two identical spectrographs, which each receives the light collected from 500 optical fibres (the bundle of 1,000 optical fibres, is essentially split in half between them).

“The job of the spectrographs is to then split the light collected by the optical fibres into different colours, so astronomers can study in detail the properties of the astronomical objects they are looking at.

"Data from the spectrographs gives astronomers information about things like mass, composition, velocity and position – and it’s this type of knowledge that will enable astronomers using MOONS to answer questions like: Why is our Milky Way a spiral?”

MOONS vacuum vessel: In numbers

  • Internal volume: 16m3
  • Weight: 3,100kg
  • Material: Aluminium
  • Dimensions: 2.4 x 2.6 x 3.8m
  • Cooled to: 120 Kelvin cold (-151.3°C)

Why does the vacuum vessel need to be so big?

“In its lifetime MOONS is expected to observe in the order of ten million objects. And with 1,000 optical fibres, observing 1,000 celestial objects, at the same time!... that’s a powerful instrument and a lot of data!

“To deliver on that magnitude of celestial observing, MOONS needs not only to have very fast optics, but optics that are extremely large too. The camera lenses themselves are about 40cm in diameter!

“MOONS also observes in the infra-red; a tricky wavelength to observe in, because at ambient room temperature, everything gives off infra-red heat. The MOONS spectrograph therefore needs to be cold, really cold – 120 Kelvin cold, which is -151.3°C. We don’t want the instrument to essentially see itself. So, 4,000L of liquid nitrogen will be pumped into the MOONS cryostat to cool it. That’s quite a volume! We’ve even had to build a new bunker to store this much coolant.”

“Huge optics; an immense liquid nitrogen cooling system to both cool and maintain the temperature within the vessel; the spectrographs, detectors, cameras… are just some of the components of the MOONS spectrograph that are driving its size.”

You’re at an exciting stage of the project where everything is being assembled into the vacuum vessel. What’s happening?

“1. Firstly, the vessel has been lined with a multi-layered insulation (MLI) blanket. Insulation is a crucial part in maintaining the spectrograph within the MOONS cryostat at its optimal operating temperature.

“2. Next the radiation shield is moved into place within the vessel

“3. Then the optical bench will go in.
The optical bench is where the spectrographs will sit – one on top, and one on the bottom.

“Here is a close-up view of the optical bench, with much of the cooling pipework installed.

“The optical bench will go inside the radiation shield, which will be placed inside its own MLI blanket.

“The MLI blanket was supplied by Jehier, in France. UK ATC team member Viv, a keen seamstress in her spare time, stitched the panels together, to fit around the shield.

“4. Next, we will do the first cool down of the system. Then we can begin the next exciting phase of installing the optics.

“We do a first cool down before we install the optics, because we need to make sure there are no leaks in the system; that all of our calculations to get the cryostat cold – to its desired temperature of 120 Kelvin, are correct; and that the cryocoolers in the spectrograph work properly to maintain that temperature. The first cool down is essentially to validate that everything is working as it should.

“It’s such an exciting stage of the project, and so rewarding to see everything being assembled and coming together.“

You think this vessel is the biggest ever made for astronomy?

“We think it is, but we don’t know for sure. So we’d love it if anyone could tell us if there is a bigger one. Certainly at UK ATC it’s the biggest we’ve ever built.

“Back in 2012 we delivered astronomical instrument KMOS to the VLT. Phil Rees our colleague at UK ATC was the Systems Engineer on KMOS (and is also the Systems Engineer, for MOONS). Watch him talk about the KMOS instrument on our STFC YouTube channel.

The vacuum chamber for KMOS is a cylinder 1.9m diameter by 1.2m tall, with a volume 3.4m3. This is less than ¼ of the volume of MOONS!

“Earlier, in 2007, we delivered SCUBA 2, which stands for Submillimetre Common-User Bolometer Array second generation. SCUBA 2, had first light on the James Clerk Maxwell Telescope (JCMT) in Hawaii 2008. It was the world’s largest sub mm camera (able to see in the 350 microns to 1.1 mm wavelengths; the wavelength band between radio and optical). SCUBA 2 enabled astronomers to see for the first time the discs around stars where planets were forming – it was ground-breaking for its time.

“The vacuum chamber in SCUBA 2 is 1.7m x 2.1m x 1.5m, will a 5.4m3 volume. This is about 1/3 of the volume of MOONS.”

“It’s a very exciting project.

What has been your journey to becoming Senior Mechanical Engineer, and leading on the engineering of the MOONS spectrograph?

“At school I loved art, maths and physics. I found that I particularly enjoy approaching design as a functional challenge, rather than an aesthetic one, and so the natural progression for me was to study mechanical design engineering at University.

“I became a chartered Mechanical Engineer, and worked in industry for a number of years. I then joined STFC, working on projects in the Daresbury Lab, in the North West, before moving to the UK ATC in Edinburgh to join the Ghost team. Ghost stands for GreenHouse Observations of the Stratosphere and Troposphere, and was a project taking astronomy tech and using it in an instrument for Earth observation – to measure the emission and uptake of greenhouse gases. Ghost sat in the belly of a NASA Global Hawk Unmanned Aerial vehicle, at altitudes up to 20,000m, above the troposphere where most of the Earth’s weather occurs.

“At UK ATC I’ve had the opportunity to work on the mechanical engineering challenges for both instruments for astronomy as well as use the ground-breaking tech we’ve developed for astronomy research, and applying that in other fields. My experience of water systems and cryogenic systems meant that I could contribute a lot of specialist knowledge to a project like MOONS.”

What has been particularly rewarding for you, working on a project like MOONS?

“The job of the engineer is to mitigate against what can go wrong – you solve one problem, and there’s always something else to worry about. Engineering as a discipline is really a series of challenges. It’s a role that keeps me on my toes, and MOONS has been no different.

“It’s been incredibly exciting working out solutions to things like: How should the vacuum pumps be sized; how will we lift the optical bench into position in the vacuum vessel; how do we work within the space constraints we have…

“Not only that, a project like this brings together many engineering disciplines as well as technicians and astronomers – both within UK ATC as well as the wider consortium. It is great to be a part of a team working together to do something that has never been done before. The design of the optics for the spectrograph, for example, is ground-breaking, and could pave the way for future spectrographs.”

Thank you Jonathan, we look forward to hearing about the next big milestone for MOONS –the cryogenic cool down.

For more information

The MOONS Consortium (VLTMOONS)

An example of international collaboration and cooperation in astronomy, MOONS is being designed and built through a consortium made up of 10 different institutions, spread across six different countries – and managed by the Science and Technology Facilities Council (STFC) at the UK Astronomy Technology Centre (UK ATC) in Edinburgh. Individual consortium partners as well as industrial partners are now delivering their components of the MOONS instrument, which is being built and assembled at UK ATC in Edinburgh. @VLT_MOONS.

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. The UK ATC has been at the forefront of previous key initiatives at the VLT, including the construction of KMOS (K-band Multi-Object Spectrograph) which enables 24 objects to be observed simultaneously in infrared light. @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

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

Very Large Telescope (VLT)

The Very Large Telescope (VLT) is the world's most advanced optical instrument, consisting of four Unit Telescopes with main mirrors 8.2m in diameter and four movable 1.8m diameter Auxiliary Telescopes. The telescopes can work together to form a giant ‘interferometer’, the ESO Very Large Telescope Interferometer (VLTI), allowing astronomers to see details up to 25 times finer than with the individual telescopes. The Unit Telescopes can also be used individually. With one such telescope, images of celestial objects as faint as magnitude 30 can be obtained in a one-hour exposure, corresponding to seeing objects four billion times fainter than can be seen with the unaided eye.

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Last updated: 20 February 2020


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