Instead of using one large dish or antenna to pick up the radio frequencies the SKA plans to use an array of millions of antennae spread out over South Africa, Australia and New Zealand to create one super sized telescope. In fact, it will be 50 times more powerful than existing radio telescopes with, as its name implies, a collecting area that amounts to one square kilometre.
You can map the universe by detecting hydrogen gas
The SKA’scentral computer will have the processing power of 100 million PCs and will be able to achieve a survey of the night sky 10,000 times faster than any existing instrument.
Cambridge Consultants, a leading technology design and development firm, has been asked to design a cost-effective antenna that will be made in the millions and be able to withstand harsh desert conditions. Humans Invent spoke to Gary Kemp from Cambridge Consultants about the challenges involved in creating these antennae.
It is a collaboration between the various international science organizations such as the STFC (Science and Technology Facilities Council) in the UK and its equivalent in other countries. Each of the countries is working on a number of pathfinder projects dealing with different aspects of the design and proving them through building smaller scale instruments.
In South Africa, for example, there has been the construction of a dish array which they call MeerKat, in Australia there was also a pathfinder project called the ASKAP programme and there have been a number of other programmes that address some of the other challenges of the telescope. Since the beginning of this year there has been a legal entity formed called the SKA Programme Office which consists of representatives of the member nations of the SKA. The relationship has become more formal and this is where more money gets put into the programme by the member nations. As a result, the detailed design of the telescope has now started to happen. They have planned to continue over the next three years and at that point the first phase of the build of the telescope will start to happen.
It picks up radio frequency signals and in particular this telescope is looking for that characteristic spectral line of hydrogen because most matter in the universe is hydrogen. You can map the universe by detecting the hydrogen gas so that is the sort of thing that radio telescopes look for. You can form images in the sky by seeing where the radio waves are coming from, just as where you can form images from where light comes from. You will ‘see’ radio images of the sky and if you were to overlay those onto an optical image you could see that they correspond. However, you get particular hotspots where the radio waves are the strongest.
How has Cambridge Consultants been involved in the project?
The University of Cambridge has been developing the antenna and receiver elements for the low frequency array, or rather the design for it. They had built a prototype and in tests it worked very well. What they then needed to do was to turn that into a design that could be manufactured in large quantities to a fairly tight budget without compromising any performance. We worked with the university to arrive at a different way of making something that works the same.
We looked at ways of making the antenna out of less metal and the most efficient solution we arrived at was to make the antenna out of bent wire. Lots of television aerials are made out of bent wire as well as supermarket trolleys and coat hangers. Supermarket trolleys and other things consist of bent wire welded together so we figured this was a winning approach for high volume, low cost products.
Part of our work was to refine the design of a bent wire version of the university’s antenna design proposing modifications to make it easy to make while they checked that with these modifications it still arrived at an electrical performance that worked well. They were running simulations based on the modifications to the antenna.
You can form images in the sky by seeing where the radio waves are coming from, just as you can form images from where light comes from
At the same time we were talking to manufacturers who bend wire for a living and make bent wire structures and welded structures to get their input on what makes a low cost and easy-to-make structure that would be strong enough to last a long time in the open air. We were going round the loop both with the university and the manufacturer and bringing that all together to arrive at something that worked for everyone.
What we have arrived at now is a complete design, an element that contains the antenna and a low noise receiver which is integrated with the antenna. This is currently being tested on a small array of 16 of these elements. The results of that will feed into a further iteration of the design. We also want to do more work on refining the design from the manufacturing side of it so maybe optimizing the choice of metals for example. One aspect of design we are going to address is considering the best way to get the signal from the antenna to the central processor.
At the moment the signals go along copper wires. Instead of doing that we might be able to take the signals through optical fibre. The benefit here is that optical fibre is very cheap while copper has become very expensive. Also, if you trail copper on the ground, then there is the risk of lightning strikes whereas optical fibre is made of glass.