Making really big telescopes

Getting better view of space

As I write this, the biggest radio telescope ever built, and maybe likely to be built for a very long time, is taking shape.

Part of it is in Africa and the other is in Australia. It will use thousands of small antennas, so the total signal collecting area will be about a square kilometre. Instruments like this are beyond the reach of single countries, so it is being built by a consortium of nations, including Canada.

The first radio telescopes were usually large dishes, which collected the incredibly weak cosmic signals and focussed them on a small antenna and radio

receiving system. The main thrust of the engineering research was how to make bigger and bigger dishes. However, there is a limit to how big a radio telescope dish can be made. To be useful that dish has to stay in shape as it scans the sky, otherwise it won't collect and focus the radio waves properly. It has to stay in shape while tilting to various angles, resist the impact of the wind, and to accommodate having the Sun warm part of the dish while the other part remains in cool shade.

Current technology can give us single dish radio telescopes up to around 100 metres in diameter. Anything bigger than that flops out of shape. Adding more steel does not help because we are adding more weight. There is a point where adding more steel actually makes things worse. We now have better, lighter materials, such as various carbon fibre composite materials. These would make it possible for us to make larger dishes, but now we have a better solution to the big dish problem, so we are using these more modern materials to make small dishes cheaper.

The workaround is since we know what happens between the radio waves hitting the antenna and finding their way to the radio receiver, we can duplicate that process digitally. We collect the incoming radio waves using lots of small antennas, trying to collect the radio waves without distorting them, and then we digitize them.

Once this is done we can do what the big dish does using digital signal processing devices. Since making huge radio telescopes in this way is so much easier than making huge dishes, why is it that only recently have we started to do this?

The answer is that the computer power needed to do this is huge. It is only over the last decade or two that we have been able to design and build the computing devices powerful enough to handle the task. Each of the thousands of small antennas making up the radio telescope produces a torrent of data. The total amount of data arriving at the processor is a tsunami, and it has to be handled immediately.

Canada has managed to establish a presence in this technically challenging field because of its work on making high-quality, small antennas, and the world's most advanced digital signal processing systems.

A few years ago, engineers at the National Research Council's Dominion Radio Astrophysical Observatory near Penticton, played a leading role in developing a digital signal processing system as a contribution to the upgrade of the Very Large Array radio telescope.

One challenge in that project was that electrical power demands of the system exceeded what the Observatory supply could provide, so it was developed and tested one part at a time. The CHIME radio telescope, located at the observatory depends on a locally developed digital signal processing system. That required a power supply upgrade.

The digital signal processing system for the new radio telescope will be an exciting challenge. This area of technology has many applications in our accelerating, digital world, so maintaining a Canadian leadership position in it is definitely a good thing.


• On March 20, the Sun will cross the equator, heading north, marking the spring equinox.

• Jupiter lies low in the sunset glow, with Venus above it. They continue to drift apart after their recent close encounter. Mars lies high in the south.

• The Moon will be new on March 21.

Ken Tapping is an astronomer with the National Research Council's Dominion Radio Astrophysical Observatory, near Penticton, B.C.

This article is written by or on behalf of an outsourced columnist and does not necessarily reflect the views of Castanet.

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About the Author

Ken Tapping is an astronomer born in the U.K. He has been with the National Research Council since 1975 and moved to the Okanagan in 1990.  

He plays guitar with a couple of local jazz bands and has written weekly astronomy articles since 1992. 

Tapping has a doctorate from the University of Utrecht in The Netherlands.

[email protected]

The views expressed are strictly those of the author and not necessarily those of Castanet. Castanet does not warrant the contents.

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