Building the Australia Telescope Compact Array

Antennas of the Australia Telescope Compact Array.
Photo: J. Masterson, CSIRO

The Australia Telescope Compact Array (ATCA) is a set of six 22-m diameter dishes (‘antennas’) for collecting radio waves from space. The antennas sit on a wide gauge rail track, so that they can be moved into different arrangements to get the best possible images of the sky for different kinds of observations. The ATCA is the only telescope of its kind in the Southern Hemisphere. It was opened on 2 September 1988.

If the ATCA had not been built, says former ATNF Director, Professor Ron Ekers, radio astronomy [in Australia] would have slowly declined … [making] a smaller and smaller contribution to the world scene.

With the ATCA, rather than becoming a backwater, Australia has maintained its position in radio astronomy. Today the telescope has observing programs related to most of the big areas of the field: the Cosmic Microwave Background, ‘dark matter’ and gamma-ray bursters, for instance.

None of these subjects were the hot topics when the telescope was being planned. As usual, the most exciting research is the stuff you don’t foresee. But the telescope can do all this today because its designers were canny.

They went for high ‘resolving power’ – ability to see detail – both for its own sake and so the Australia Telescope would complement the new infrared, optical and X-ray telescopes coming on stream, as well as the US Very Large Array (VLA), the major radio telescope in the Northern Hemisphere. They also wanted to be able to study narrow ‘spectral line’ radio signals, the signatures of many atoms and molecules that live in interstellar gas clouds and the envelopes of certain stars. Unlike the VLA or the MERLIN array in the UK, the ATCA was to have this ability built in from the beginning. And the designers made sure the instrument had wide bandwidth – the ability to study a wide range of frequencies at the same time – to cope with spectral lines that have been broadened or shifted by the Doppler effect, which happens when molecules are whirled about at a great range of speeds.

Finally, the designers also built into the ATCA the ability to accurately measure polarisation in a signal (like light, radio waves can be polarised). Polarisation is the key to mapping the magnetic fields that thread through galaxies – and which we don’t yet fully understand.

All these abilities have made the ATCA a first-class instrument. But this ambitious design evolved from something rather more modest.


The Australia Telescope grew out of a proposal for an instrument called the Australian Synthesis Telescope (AST), first suggested in 1974-75. This was to be an interferometer, built at Parkes that would extend the power of the existing Parkes telescope. The committee pulled together to work on the concept came from CSIRO, the University of Sydney, and ANU’s Mount Stromlo Observatory. For four years the committee members argued back and forth about what form the instrument should take. Some supported another large single dish, linked to the Parkes telescope. Others wanted many small dishes. By 1978 this was settled, in favour of many small dishes, but as the 70’s turned into the 80’s the project had a dwindling chance of success, not least because it seemed under-funded at only $9 million. The AST was submitted for Government approval, but was turned down.

Then in 1981 a new player came on the scene. The incoming Chief of CSIRO’s Division of Radiophysics, which ran the Parkes telescope, was Dr Robert (Bob) Frater, an electrical engineer from the University of Sydney. Frater clearly believed that, in the poet Robert Browning’s famous words, “A man’s reach should exceed his grasp, or what’s a heaven for?” He thought the AST project was too narrow in scope: not innovative enough, not sufficiently well funded, likely to have a short scientific life, and not allowing for industry involvement. And there were some concerns about Parkes as a site.

So in 1981 there was a change of plan. The site of the new telescope was switched to Narrabri, to the observatory housing Radiophysics’ radioheliograph, an instrument for studying radio waves from the Sun, which was going to be closed down. This location meant that the new telescope could form part of a ‘long baseline array’: putting the telescopes at Narrabri, Parkes, and Siding Spring Mountain near Coonabarabran would form an excellent 3-element array, with almost perfect spacings between the three sites.

And there was a new design for the telescope too, one that could accommodate the needs of many groups in the astronomical community: for high-frequency spectral-line mapping, for covering a wide range of wavelengths, and for Long and Very Long Baseline Interferometry (VLBI). This was the Australia Telescope essentially as we know it today. The Australian astronomical community gave it the thumbs up.

Then came several months of lobbying. Frater, as Chairman of the project’s steering committee, nailed his colours to the mast by undertaking that 80% of the project’s funds would be spent in Australia. The Federal Government finally approved funding in August 1982. With this achieved, the group that had guided the project to this point met for the last time on 26 October 1982. The last note in that meeting’s minutes reads “Adjourn for champagne at 16.30.” The relief was premature: a change of government in 1983 put the project on hold once more. But after several anxious months, and a hearing by the Parliamentary Public Works Committee, Cabinet approved the project in November 1983.

Bicentennial project

Five years of hard work followed. The Telescope had been designated an official Bicentennial project: it had to open in 1988, come what may.

CSIRO worked closely with the consulting engineers, Macdonald Wagner and Priddle (now Connell Wagner), to come up with two new designs for the antennas – one for the six antennas near Narrabri, and a slightly different version for a seventh antenna to be built near Coonabarabran.

These designs, and techniques for making components of the antennas, such as the surface panels, were transferred to industry. The design innovations and engineering excellence shown in the final Australia Telescope made it a showcase for the Australian industries involved.

The antenna story is a key one, recalls Frater. The first use of the ATCA designs in satellite-communications antennas was at the OTC (Overseas Telecommunications) tracking station at Gnangarra in Western Australia. This, says Frater, was a major breakthrough that led on to our antennas being used in Vietnam, spearheading the movement of Australian telecommunications expertise into the Asian arena. The financial benefits flowing from all of this amount to many tens of millions of dollars.

The Australia Telescope and these associated projects have had a very definite ‘we really can do it’ effect on wireless telecommunications in Australia.

The telescope’s final cost was $50 million (1988 dollars). The first correlated signal – the equivalent of an optical telescope’s ‘first light’ – came in August 1988, one month before the official opening

The opening

2 September 1988 dawned bright and fair, but with a wind that could have blown the hair from a horse.

With the Narrabri band playing the theme from ‘Star Wars’, an antenna trundled down the track to the ceremony, carrying a load of VIPs, including the then Prime Minister, Bob Hawke. “Surely you get to open lots of interesting events,” commented Project Engineer John Brooks to Hawke. “Not like this,” said Hawke warmly. “Not like this.”

Disembarking, the speakers were installed on the podium: Neville Wran, the then Chairman of CSIRO; Barry Jones, the Minister for Science; Bob Frater; Bob Hawke. Hair whipping around in the wind, voices blown away from the podium mikes, they spoke of vision and hard work. Frater was first: Prime Minister, we have delivered. The project had come in on time, within budget, and with 80% Australian content.

The telescope was declared open for business, then three antennas slowly tipped, spilling out streams of green and gold balloons that whirled away into the sky.

And after it was all over, there was, of course, a party. A big party. Some way into it, a storm broke. When the floor of the outdoor marquee became sodden, the dancing shifted to the tabletops. Outside, CSIRO photographer John Masterson waited patiently to capture the sign of heaven’s approval: a rainbow.

Great expectations …

So how well has the Australia Telescope met the great expectations astronomers had for it? One of its users, Professor John Dickey of the University of Minnesota, puts it this way:

I think the greatest contribution of the ATCA to world astronomy has come not just from its being the only instrument in the Southern Hemisphere which can make detailed maps in the centimetre wavelength range, but from its being the only aperture synthesis instrument designed and built in the 1980s, with modern electronics and computer controls. This has allowed it to really lead the way in astronomical techniques, beating [other northern hemisphere telescopes] to new discoveries and new techniques … which the older Northern Hemisphere instruments were not flexible or powerful enough to do.

And Bob Frater:

The array has met expectations beyond my dreams! It was rapidly appreciated by the scientific community that we had a world class instrument … I haven’t heard any negatives about the AT [Australia Telescope] all the way along from when we started to build it, but have had lots of very positive comments. … I am, of course, delighted to have had the opportunity to build the AT with the fabulous team that we had. It is an experience that I will always cherish.