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Australia Telescope Compact Array

The Australia Telescope Compact Array (ATCA), located at the Paul Wild Observatory near Narrabri, is a set of six 22-m diameter dishes (‘antennas’) for collecting radio waves from space and is the only telescope of its kind in the Southern Hemisphere. Costing A$50 million, the Compact Array was built to keep Australia at the forefront of radio astronomy. It was an ambitious project, with the aim of building a world-class array with 80 per cent Australian content. In 1983 the then Chief of CSIRO Radiophysics, Bob Frater, selected engineer John Brooks as the man who could make this happen and appointed him as Project Manager. Under John’s leadership, this goal was achieved, culminating in the opening of the Australia Telescope Compact Array by Prime Minister Bob Hawke on 2 September 1988.

The ATCA was designed and built in Australia, with high content of locally built components. The leading edge engineering that went into it has had spin-off benefits for local industry, especially in communications and the space industry. The ATCA is part of the Australian Telescope (AT) where its six receivers at Narrabri are linked to the Mopra antenna (also 22-m in diameter) near Coonabarabran and the 64-m diameter radiotelescope at Parkes. Such linking creates a virtual telescope hundreds of kilometres in diameter, able to see much more detail than any of the individual telescopes. Since 1989, the Australia Telescope has been run as a national facility ‘ the Australia Telescope National Facility (ATNF) ‘ open to use by Australian and overseas astronomers.

For his role in the construction of ATCA and subsequent upgrades and additions to ACTA and the Parkes Telescope, John Brooks was awarded a CSIRO Medal for Research Achievement in 1988 and a CSIRO Lifetime Achievement Award in 2002.

The original proposal is turned down

Australia has been at the forefront of radio astronomy since the end of World War II. Pioneering work was carried out by scientists from CSIR, the forerunner of CSIRO, who were previously engaged in wartime radar research (see Radar for more information). The group’s achievements along with the construction of a number of fine radio telescopes (including the one at Parkes), by CSIRO and some universities, kept Australia at the forefront of radioastronomy for the next 30 years.

However, by the 1970s the existing telescopes could not operate at the high frequency required by leading-edge research at that time. Other countries were also building new generation telescopes that threatened the vitality of Australian research.

In 1975, CSIRO and a group of universities developed a proposal for a high-resolution radio telescope, the Australian Synthesis Telescope (AST). 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 the Australian National University’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 1970s turned into the 1980s 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.

A change in plan

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 famous words of poet Robert Browning:

A man’s reach should exceed his grasp, or what’s a heaven for

Frater 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. In addition 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 The Division of 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’. Placing the telescopes at three different sites ‘ Narrabri, Parkes, and Siding Spring Mountain (near Coonabarabran) ‘ would form an excellent 3-element array, with almost perfect spacings between the three locations.

And a new design

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
  • covering a wide range of wavelengths
  • Long and Very Long Baseline Interferometry (VLBI).

The Australian astronomical community gave the new design the thumbs up.

The fight for approval

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 to showcase Australian technology. A master-stroke of strategy was Frater’s decision to name the proposal the Australia Telescope and nominate it as a Bicentennial project. 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 with close collaboration between CSIRO and industry

The Telescope having been designated an official Bicentennial project, had to open in 1988, come what may. Five years of hard work followed. As Brad Collis wrote in his book Fields of Discovery ‘ Australia’s CSIRO (pp.404):

The design and construction of the ATCA, its instruments and its software was the most technologically-challenging project ever attempted in Australia and a far cry from the rudimentary pre-computer technology which drove the Parkes telescope when it was built. For example, the building of the Australia Telescope involved the first use of fibre-optics in Australia and it required the design and mass manufacture of the most sophisticated microchip that had been designed and made anywhere at that time. The Correlator Chip had to process all the information coming from all of the antennas and sort the signals from background noise ‘ at a processing speed of two trillion multiplications per second. The chip was designed in-house, fabricated by Australia’s first VLSI company (Austek), and projected the mechanics of radio astronomy far into the twenty-first century.

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 (the Mopra 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. As Bob Frater recalled:

The antenna story is a key one. 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 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.

John Brooks on site

John Brooks on site. [Source: CSIRO ATNF]

In his book Fields of Discovery ‘ Australia’s CSIRO (pp.404-405) Brad Collis summarises the challenges that had to be overcome:

The whole basis of an array is that only the signal being tracked is common to every antenna. By correlating all the data from all the antennas, the common signal can be separated out. All of the project’s key components were designed and manufactured within the Division of Radiophysics or by Australian industry. The telescope’s engineering manager John Brooks, said the project required a level of precision and quality control probably unprecedented in Australian civil engineering. For example, the 3-kilometre-wide gauge rail track laid on thousands of tonnes of granite ballast had to be accurate to within plus or minus 0.5 millimetres from end-to-end while accommodating the curvature of the Earth.

John Brooks recalled:

The whole project relied on these telescopes running up and down a railway line and the 35 concrete ‘stations’ on which to stand when these observations are being made. These stations are concrete piers sitting on bedrock and there was absolutely no margin for error. One day one of the concrete teams poured without waiting for the Connell Wagner site supervisor to check the forming. He made them jack-hammer out several cubic metres of concrete at the bottom of an eight-metre hole. That was the level of quality control that was required. Nothing could be taken for granted.

The final cost of the compact array was $50 million in 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.

Construction of the Australia Telescope Compact Array

Construction of the Australia Telescope Compact Array, Narrabri, NSW. [Source: CSIRO ATNF]

The ATCA opening in 1988

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.

Project Engineer John Brooks remarked to the PM’s wife, Hazel Hawke, that the PM must go to many of these ‘Opening do’s’ and she replied: Not like this John, not like this

Disembarking, the speakers were installed on the podium. They were: Neville Wran the Chairman of the CSIRO Board and former premier of NSW; Dr Barry Jones, the Federal Minister for Science; Bob Frater and the PM 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

Professor Ron Ekers was appointed the Foundation Director of the Australia Telescope National Facility and returned to Australia to take up that position in 1988. Before joining CSIRO he had been, from 1980 until 1988, the Foundation Director of the Very Large Array, the major national radio telescope in the USA. At CSIRO, Ekers established the ATNF as a world class National Facility.

As one of its users, Professor John Dickey of the University of Minnesota, said:

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.

Five antennas of the Australia Telescope Compact Array

Five antennas of the Australia Telescope Compact Array, near Narrabri, NSW. [Source: CSIRO ATNF]


The Compact Array has had three major technical upgrades. The most obvious to users has been the outfitting of the Compact Array to handle 12- and 3-mm wavelengths enabling it to take detailed pictures of evolving galaxies and the birthplaces of young stars. This was a major overhaul, funded by the first round of the Commonwealth Government’s Major National Research Facilities (MNRF) program over several years, and involved creating new receivers, building the north spur track, resurfacing the antennas, and reconfiguring the Local Oscillator (LO) distribution system.

Completed in November 2000, it made the radio telescope the first millimetre-wave ‘interferometer’ in the southern hemisphere and the first anywhere with this technology giving astronomers in the southern hemisphere a ringside seat looking straight into the centre of our own galaxy and at the two nearest galaxies, the Magellanic Clouds.

The chip at the heart of the new receiving system is a ‘monolithic microwave integrated circuit’ (MMIC) made of the exotic material indium phosphide, cooled to 20 K (-253 °C). It is one of several components jointly developed by CSIRO’s ATNF and the CSIRO Division of Telecommunications and Industrial Physics, under a special program established by former CSIRO Chief Executive Malcolm McIntosh. For more details, see Radio astronomy amplifiers using millimetre wavelength imaging.

The second upgrade, completed in 2008 and done in collaboration with NASA, has given the Compact Array an additional 7-mm capability for both astronomy and spacecraft tracking.

The third upgrade, completed in 2009, was the Compact Array Broadband Backend (CABB) project which was funded by a second round of the MNRF program. Both the millimetre-wave upgrade and CABB competed successfully in their respective MNRF rounds against bids from all areas of Australian science, not just astronomy. See also The Compact Array Broadband Backend (CSIRO ATCA).

Continuing contributions

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. The designers 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. As former ATNF Director, Professor Ron Ekers stated:

If the ATCA had not been built, radio astronomy in Australia would have slowly declined … making a smaller and smaller contribution to the world scene

In 2008, on the 20th anniversary of the opening of the ACTA, Phil Edwards ATNF’s Head of Science Operations retrieved from the Astrophysical Data System the top 12 most highly cited papers using Compact Array data, all with more than 100 citations. These are listed in the ATCA publications section.

Details of achievements from ATCA, some of which are listed in the ATCA publications section, can be found at the Australia Telescope Outreach and Education website.

Technology driver

As Mr Malcolm Sinclair, Head of the Australia Telescope Receiver Group explains:

Astronomy is a technology driver. This technology is a showpiece for Australia, benchmarked against the most advanced systems in other countries.

The same technology that Australian scientists use to explore the universe will also help keep Australia at the forefront of the global information technology and telecommunications industries. As Dr Alan Young of CSIRO Telecommunications and Industrial Physics said at the ACTA upgrade ceremony in 2000:

Millimetre waves are the next area of commercial interest as users go to higher and higher frequencies. Carriers in Australia alone have recently spent around $80M buying spectrum at the edge of the millimetre region. CSIRO is working with both carriers and leading-edge suppliers on next-generation technologies. Some of the background expertise came from radio astronomy.