Date: May 13, 2010
Title: The Square Kilometre Array
Podcaster: SKA Outreach Team
Description: The Square Kilometre Array will be the world’s largest scientific instrument and building such an enormous telescope presents challenges that call for innovative engineering. Jo Bowler, outreach officer for the SKA, talks to Peter Hall from the International Centre for Radio Astronomy Research in Australia and Justin Jonas of Rhodes University in South Africa, about the design of the telescope, the practicalities of banning mobile phones and the benefits that the SKA will bring beyond astronomy.
Peter Hall is Professor of Radio Astronomy Engineering at Curtin University of Technology. He is a Fellow of the Institution of Engineers (Aust) and, until his appointment at Curtin in 2008, was foundation International Project Engineer for the SKA. He led CSIRO’s SKA program from 1999-2003, was responsible for the initial Australian SKA site submission, and now holds executive positions in the Curtin Institute of Radio Astronomy (CIRA) and the new International Centre for Radio Astronomy Research (ICRAR). Peter has been responsible for many policy and technical decisions in the SKA project and has an unequalled knowledge of the international and Australian factors involved in this mega-science endeavour. He is an expert in SKA system design, key technologies, industry engagement and infrastructure development.
Professor Justin Jonas is the Associate Director for Science and Engineering in the SKA South Africa Project Office. His responsibilities include ensuring that the MeerKAT telescope has the appropriate specifications and uses the most appropriate technologies to achieve its scientific goals, liaison with the international SKA scientific and engineering communities, and technical assistance with the establishment of the Karoo Radio Astronomy Observatory. He is also Professor of Physics and Electronics at Rhodes University, and was Director of the Hartebeesthoek Radio Observatory (HartRAO) for a three-year period. Justin has been a member of the SKA Science & Engineering Committee (SSEC) since 2002, and is currently on the Executive of this committee.
Jo Bowler is the Outreach Officer for the Square Kilometre Array telescope. Based in the project development office at the University of Manchester, Jo coordinates outreach activities to raise the profile of the SKA across the world. Along with the international SKA Outreach Committee, she produces materials about the ground breaking engineering required to build the SKA and the astronomy research that will be possible with the world’s biggest telescope.
Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by Elizabeth Fracek (FRAY-SEHK), and dedicated to the Smithsonian Air and Space Museum. Someday I’ll get past the lobby, I promise.
The Square Kilometre Array Transcript
When completed in 2023, the Square Kilometre Array, or SKA, will be the largest radio telescope ever constructed. It will enable astronomers to study the formation of the first stars and galaxies in the early Universe, shedding light on the birth, and eventual death, of the cosmos. The larger a telescope is, the more photons it can collect, and the more sensitive it is. The Square Kilometre Array is so-called because, although it will be spread across several thousand kilometres, it will have a total collecting area of one square kilometre, making it extremely sensitive. Australia and South Africa are the finalists of an international competition to host the SKA and a decision will be made on its location in 2012. We talked to Peter Hall at the International Centre for Radio Astronomy Research in Australia, and Justin Jonas of Rhodes University in South Africa about the design of the telescope.
1. Why build the SKA when there are other existing large telescopes?
Modern astronomy is very much about astronomy across the wavebands of the electromagnetic spectrum and the SKA is one of a suite of complementary new generation telescopes which are now being built or will be built in the next decade. Effectively we need to build these new large instruments in order to keep the discovery rate alive in astronomy and to maximise the physics output from the science.
2. What is the benefit of many small receivers, or antennas, instead of fewer large ones?
There are a number of reasons for going for lots of small antennas rather than one large one. The most obvious one is cost. It turns out to be cheaper to build up a telescope out of lots of smaller units rather than trying to build one big one. There are other technical and scientific reasons for wanting to do that as well. One of the things is that the smaller telescopes give us, intrinsically, what’s called a larger field of view; we can actually see a larger patch of sky at any one time with a lot of little dishes rather than one big dish. It gives us the flexibility to split the telescope up into a number of different sections so you can look at different parts of the sky with different dishes and it allows you then to spread these antennas out over a very large area and connect them together as an interferometer and that then allows us to get extremely high resolution on the sky which you wouldn’t get from one collected aperture or one large radio telescope.
3. Can you briefly describe the three types of receptor, or antenna, that will be used and explain why we need three different types?
The one type of antenna that we will be using is what people normally associate with radio astronomy and that’s the dishes. As we said earlier there are going to be lots of fairly small dishes or medium sized dishes, say 15 m dishes. These are reflecting surfaces that concentrate radio waves from the area of the antenna on to a receiver. This has been the traditional way of doing radio astronomy and this will be used at the higher frequencies or what we call the mid frequency and the high frequency part of the SKA. This is the fairly traditional way of doing things. As you go to lower frequencies it becomes impractical to use dishes because the dishes have to become very large and as they get larger and larger they get more and more expensive. So we move into a class of antennas called aperture arrays; these are non-steerable antennas. They are just arrays of very simple antennas that are placed on the ground and we use electronics to steer the beam around the sky rather than mechanics as we do with dishes. To steer a dish around you need a mechanical mount and that allows you to point the thing somewhere in the sky. The aperture arrays just lie flat on the ground, don’t move and we use electronics to steer the beams around; they are used at the low frequencies. Now in turn, the aperture arrays are split into two different types of aperture array. There is the dense aperture array, a tightly packed aperture array, and the sparse aperture array. This pretty much says that in the one case the antennas are very closely spaced to each other whereas the sparse antennas are spread out more. The dense antennas, the dense aperture arrays, operate in a frequency range of something around about a GHz, or 1000 MHz, down to something like a few hundred MHz – so in that sort of range. Then the sparse aperture arrays we use at the very lowest frequencies so below 400 MHz or below 300 MHz somewhere around about there, down to as low as 10 MHz. So the categories of antennas fall into two broad groups, the dishes which have mechanical steering, and the aperture arrays which have electronic steering. Then the aperture arrays again are split into the dense and sparse aperture arrays. The dividing line between each of these, the frequencies where they swap over from one technology to another, is something that is under discussion at the moment. It is one of the things that the SKA working groups are working on, to say where is the optimum place to do that? Basically that optimisation is driven by scientific requirements and also by cost. How much is it going to cost to implement this technology at this frequency range versus another one and what is the scientific return on that? The big advantage that the aperture arrays give you is that they look at very large pieces of sky. They have very large fields of view. You can literally see the whole sky with an aperture array at any one time which means that if there is any strange thing that happens up in the sky, you are going to catch it, whereas the dishes when they are pointing in any one direction, they can’t see what is happening behind them. So there are big advantages of going to the aperture arrays but in turn the aperture arrays are not practical at the higher frequencies because you have to have a very large number of elements and the costs become literally astronomical.
4. Data from each antenna has to be transferred back to a central processing computer. Is there really going to be an optic fibre cable running from each antenna to a central computer?
Yes there will be an optical fibre from each antenna but outside a region of perhaps a few hundred kilometres the optical fibres will be owned by the telecommunications carriers and leased by the SKA project under various arrangements.
5. How can the radio quietness of the site be ensured? Won’t the locals want mobile phones?
Yes that’s a good question. I think the real answer is to go where there are very very few locals and that’s the reason why we in Australia have gone to the Murchison region. I believe the entire shire, which is more than the size of The Netherlands, has a population of about 120 people. It is true that people will need some form of communication for safety and other reasons in that general region and in most cases that will easily be accommodated by shifting the services onto a different carrier network perhaps a different frequency of mobile communications or hopefully for many of them into fixed optical fibre landlines and so on.
Both candidate sites are in very remote areas, chosen to be remote because there are very few people there, and also chosen in areas where there is really no chance of economic development in the future. So they are in areas of dwindling populations to start off with, so the locals are largely sheep – and other animals wild and domestic – and very few people. So that is the first mitigation, you have fewer people there. On top of that you have legislation. In South Africa we have legislation which allows us to limit what transmissions happen in quite a large area of the Northern Cape province of South Africa and the Australians have something similar in Western Australia. So you have the law on your side but of course then you have to take into account the needs of people who are still in the area for health and safety reasons so we look at alternative technologies for communications for the local population. Have radio systems; you can’t get away from having radio systems in the end for health and safety and you ensure that you can manage them in such a way that they have the minimum impact on the telescope. Either operating in frequency ranges which are not interesting to the SKA or if possible using satellite systems or various other technologies that we’re looking at.
6. Apart from radio astronomy, what benefits is the SKA likely to provide?
Well there are obvious ones such as spin offs to industry. Radio astronomy has traditionally been an incubator for the very highest technology and has actually a very good track record in spinning off technologies to industry. Also there is the obvious one, I guess, of the procurement opportunities. The SKA will be a large project and many companies around the world will be in a position to provide goods and services to the project. In fact the project can only be built with a very large industry involvement as is true of most of these big mega science projects. I guess the other, perhaps less obvious, ones are things like the availability of the distributed sensor network in order to do more exotic science around whichever continent the telescope is located on. The SKA has all these fibres around, we have very high data rates, and consequently we have quite a bit of capacity to support other scientific and related experiments. So one can imagine all sorts of geophysical, geoscience, and exploration type activities being supported across the SKA sensor network. So I think that there are many opportunities that come from the commercial world right through to the scientific use of shared facilities.
I think that there are generic benefits that any scientific experiment has and they are very wide ranging. Some are sociological things – when you are exploring the Universe, I think that really does have an effect on the wider population – understanding how the Universe works. In the candidate countries, wherever the SKA goes, it will definitely inject investment into the areas. We are seeing already, certainly with MeerKAT in South Africa, that the towns in the area of the SKA, as I said they have dwindling populations but still there are people there, and we have injected some new excitement into that area. People are looking at opportunities that they can get from MeerKAT to have things like outreach centres, have bed and breakfasts for visiting staff members who need to stay in places, so the benefits are very wide-ranging I think. We have driven technology as well. If you look at the technologies that the SKA is requiring, these have generic applications in other areas too. Certainly in South Africa this is one of the reasons that the government is funding the project, and is encouraging us to be involved in the SKA, is that it sees it as a mission driven innovation project. So I think there’s a very wide range of ways that the SKA will affect different communities and I think some of them we can’t even predict. We’ll see when this thing happens, that we’ll say “Gosh I didn’t imagine that we would have that sort of influence on people”. I think that a very very important one though is outreach. You need these big projects to excite young people to become involved in science. I think it’s particularly the case in South Africa but I know in other countries around the world, there is increasing difficulty in getting people to get excited in science and technology.
If you’d like to find out more about the SKA please visit us at www.skatelescope.org where a full length version of this interview is available.
End of podcast:
365 Days of Astronomy
The 365 Days of Astronomy Podcast is produced by the Astrosphere New Media Association. Audio post-production by Preston Gibson. Bandwidth donated by libsyn.com and wizzard media. Web design by Clockwork Active Media Systems. You may reproduce and distribute this audio for non-commercial purposes. Please consider supporting the podcast with a few dollars (or Euros!). Visit us on the web at 365DaysOfAstronomy.org or email us at info@365DaysOfAstronomy.org. Until tomorrow…goodbye.