Adventures in ELT Wonderland

Snazzy artist's rendering of the E-ELT, VLT and the Atomium

Optical and infrared observations are the bread and butter of astronomy. For thousands of years the earliest scientists were inspired by the light coming from the sun and the night sky, the light they could see with the unaided eye. These observations have shaped our vision of the world throughout history. Using modern telescopes we can see far beyond the wavelengths visible to the naked eye, catching the photons from the most distant known objects in the Universe, from radio waves through to the most energetic gamma rays. But it’s optical and infrared images, like those produced by the Hubble Space Telescope, that still prove the most inspiring to many scientists and the public.

For the past 2 years I’ve been involved in the planning of the next generation of optical/IR observatories, the European Extremely Large Telescope or E-ELT. Specifically, I work on the design of a potential instrument for this mammoth of a telescope, whose 42-m primary mirror diameter will be four times larger than the largest optical telescopes in the world today. Previous generations of telescopes have always seen an approximate doubling of mirror size, and this new generation of observatories signal an important departure from this trend – a hugely ambitious endeavour by all accounts.

Working on the E-ELT is really quite fascinating, if only for experiencing the process of development and the amazing momentum such a huge project can gather in a short period of time.  But it’s not all unbridled ambition and starry-eyed wonder: designing an instrument for a telescope that does not yet exist, many of whose specifications are unknown, indeed whose funding is still uncertain, presents some very unique challenges. And by “unique” I mean head-on-desk-banging-ly frustrating. This is not me having a bad week at work or having a dig at thepeople I work with, by the way, it’s simply a consequence of the nature of the project and the distribution of work between the central organisation and its many member countries. In fact, my co-workers’ experience, professionalism and occasional humour make the whole process bearable, even quite enjoyable, for a young ‘un like me.

Crowdsourcing the professionals

The European ELT project dates back almost a decade, and after successive redesigns finally received the green light from its governing council to go ahead with a detailed design phase in December 2006. Like its predecessors such as the VLT, Gemini and Keck telescopes, the E-ELT is not a “science-specific” telescope, designed instead to enable advances in the broadest possible range of topics in optical and infrared astronomy. Based on a roadmap of scientific priorities for the next decade, assembled by a team of senior European astronomers , ESO then issued “calls for proposals” from the European community to study a number of instrument concepts. These calls go something like this (I paraphrase):

“Dear astronomers, as you know we’re building a giant optical/IR telescope that looks something like this [big telescope image] although we’re not exactly sure of many of the details yet. We think the telescope would do great science when paired with an instrument that can carry out high-resolution spectroscopy at optical wavelengths over large fields of view, and we’re looking for someone to come up with an appropriate design in the next 18 months. If you think you’re up to designing such an instrument, please tell us who you are and what you intend to do. If we like your plans, we’ll give you some money to help you on your way. Thanks and good luck, ESO”.

These calls don’t come out of the blue:  ESO’s communication with the astronomers in their community is such that they will already know at the time of the call who is likely to respond; indeed these same astronomers helped define the potential instrument suite for ESO in the first place, or have built instruments for existing telescopes in the past. There just aren’t that many of us for it to be a fully open competition. What’s more, these projects are so large and the community so small, that consortia need almost everyone in the field involved with manpower and funds to make the study a success.  Once ESO is satisfied that the team is basically up to the job, money and contracts change hands and the fun begins.

Your telescope has detected new hardware

As an organisation, ESO have developed a standardised approach to instrumentation: they deliver the telescope with fixed and clear interfaces to allow instruments to be installed rather like plug-and-play devices in modern computers. The reasoning is that this minimises the time needed for installing and aligning the instrument at the telescope. No muss, no fuss. The approach has proven very successful with ESO’s current powerhouse observatory, the VLT in Chile.

But for the E-ELT this method is proving more difficult. For one, the E-ELT is being designed in parallel with its instruments, so many details of its capabilities are still uncertain or entirely unknown. Interface definitions are continually updated and refined. And, let’s be clear, the E-ELT is enormous, unlike anyone has ever built for optical astronomy. Its instrument-bearing platforms alone are around the size of a tennis court.

So when a problem or question arises in the instrument team about the capabilities of the telescope, an answer is often not readily available. An email gets bounced around Garching and the rest of Europe, gathering 50 widely differing opinions, and all the while the instrument team stand around collectively headscratching. And the questions go in both directions between ESO and the teams. Eventually a tentative answer comes out of such a discussion, and so progress is made is teeny tiny baby steps. When new information becomes available, everyone goes back to see what this means

In the ELT era, telescopes and instruments will simply not be able to behave like separate entities. The incredible resolution that the telescopes are capable of delivering just by their sheer size makes them more sensitive to other problems, such as misalignment of mirrors, vibrations from the wind or turbulence in the atmosphere. The only way these effects can be managed is by continuous active control of the optics using careful monitoring of the weather, local environment and optical quality throughout the telescope’s operations. Rather than just receiving the telescope’s signal and processing it, the instruments now have to communicate and interact with the telescope control system. This requires a much more complex control architecture than has so far been needed.

The future is dark

ESO will take a very important step in their road to the E-ELT later this year when they decide on the location for the telescope. It will be the last of the three major ELT projects to do so: the 24-m Giant Magellan Telescope will be housed at Las Campanas, an existing observatory in Chile, and the California-based Thirty Meter Telescope recently announced Mauna Kea in Hawaii as its home . Finding a suitable site for a new observatory is in itself a fascinating process that encompasses politics, anthropology, environment, more politics, geology, meteorology, logistics, diplomacy and lots of politics.

Infrared observers in particular will be hoping for a nice high and dry site, similar to Mauna Kea in Hawaii or Chajnantor in Chile, to provide the clearest and darkest possible infrared skies. Infrared radiation is absorbed by water molecules in the atmosphere and IR astronomy is therefore far more sensitive to the presence of water vapour in the atmosphere over the telescope.

The E-ELT instrument studies will all be concluded and reviewed by early 2010. After that there will be a hiatus before ESO will decide on an instrumentation plan for the telescope and which ones specifically to take forward into a next phase (cue champagne and cheers). Then the real fun begins.

Image: ESO