• Marina Joubert
SKA South Africa communications
+27 83 409 4254
Now that the long wait is over and the co-hosts of the Square Kilometre Array (SKA) have been announced, South Africa and Australia can get on with the business of building the world’s biggest scientific instrument.
Although the site is to be shared, the split is not equal – Southern Africa will get the juiciest part of the SKA pie.
The technology will be rolled out in two phases. Actual construction of the SKA is expected to start in 2016, with mid-frequency antennae – the big dishes similar to those seen in the KAT-7 grouping, now operational at the local SKA site – and an array of low-frequency antennae making up the first phase.
Phase two will commence in 2018 and will continue up to 2023.
“Scientists should be able to use phase one for research by 2020,” said Prof Justin Jonas, associate director for science and engineering at SKA South Africa. “By that time construction on phase two should be underway, with full science operations commencing by 2024.”
The SKA was always perceived as a two-phase project, said Jonas.
“Even if one country had hosted the whole thing, the phases would have been built at a distance from each other,” he added. “Now the phases will just be further apart.”
He said the technology differs for each component, and they operate independently.
Southern Africa’s core site is deep in the Northern Cape province, sitting at an altitude of 1 000m and located about 100km west of Carnarvon, a sleepy Karoo town. This site is not only quiet in audio terms, but more importantly for the SKA, it’s a radio-quiet area that’s legally protected by the Astronomy Geographic Advantage Act of 2007 to keep it that way.
From the core of about 1 500 antennae, another 1 500 or so will radiate out to other parts of South Africa and Southern African countries, some as far out as 3 000km away. The partner countries are Namibia, Botswana, Ghana, Kenya, Madagascar, Mauritius, Mozambique and Zambia.
The core site down under, on the other hand, is at Boolardy, a former sheep station about 100km west of the mining town of Meekatharra. This remote town lies about 770km northeast of Perth in Western Australia.
This gigantic scientific instrument will have a combined collecting surface of one square kilometre, and will be 50 times more sensitive and 10 000 times faster than anything else yet built.
In South Africa, data gathered from all these far-flung receivers will be processed locally. But, said Jonas, computers from all over the world could conceivably work on the data.
“So everybody will get something out,” he said.
The world’s most sensitive radio telescope
The KAT-7 is the precursor to the MeerKAT, an array of 64 dishes which in turn will form the beginnings of the SKA. MeerKAT was acknowledged in the SKA site advisory committee’s report as a crucial step in the implementation of the SKA.
Australia’s equivalent of MeerKAT is called ASKAP – the Australian SKA Pathfinder, which consists of 34 dishes. Both test sites have used mid-frequency instrumentation to demonstrate their technology.
“The MeerKAT will supplement the sensitive SKA phase one dish array, providing a large part of the collection area of the world’s most sensitive radio telescope,” said South Africa’s science and technology minister Naledi Pandor at a briefing to announce the final hosting decision.
“We have always said we are ready to host the SKA – and the world has listened.”
Pandor has been widely hailed for her leadership throughout the initial and bid processes, which took about nine years to get to the decision-making stage.
So who gets what?
Three different types of antenna technology will be used to cover a wide range of frequencies between 70 megahertz and 10 gigahertz – they are the mid-frequency dishes, and the low- and mid-frequency aperture arrays.
The aperture arrays are cost-effective to build and run, and can observe more than one part of the sky at the same time.
With each standing about 1.5m high, the low-frequency aperture arrays can be accommodated in a relatively modest area, compared to the bigger 15m-tall dishes. A baseline of 200km would suffice, according to SKA.
The South African part of phase one, the whole of which constitutes about 10% of the total SKA, will include the 64 dishes of the MeerKAT, plus another 190 dishes.
Across the Indian Ocean, the ASKAP too will be absorbed into phase one. In addition, 60 mid-frequency dishes and an as yet undisclosed number of low-frequency aperture arrays will be installed.
In phase two, all the dishes will be built in Southern Africa – this is the stage at which the widely-spaced dishes will start to spread into the partner countries, out to a distance of 3 000km or more from the core. A number of flat, 60m-wide mid-frequency aperture arrays will also be built here – the number will be determined later.
The rest of the low-frequency aperture array antennae , as many as 10 times more than in phase one, will be constructed in Australia and New Zealand.
“The higher elevation of the South African site is an advantage for the mid-frequency telescope, hence the allocation of this segment of the SKA to South Africa,” said Jonas.
It means that South Africa will have the ability to make lengthy, deep observations of a narrow part of the sky, while Australia will be able to more quickly make surveys of wider portions.
In terms of costs, he said, members of the SKA organisation – South Africa, the UK, Australia, Canada, China, Italy, New Zealand and the Netherlands – will all contribute to capital and running costs. Depending on whether new members come on board, these costs may vary.
A worldwide network of supporting elements, including staff, scientific institutions, data networks and computing facilities is also now needed, said Jonas.
The hosts will now enter a design and pre-construction phase before the SKA begins to take physical shape.
South Africa will also press on with the MeerKAT which, said Pandor, would have gone ahead whether or not the country had been awarded the SKA.