SA’s MeerKAT and the international SKA telescopes moving from concept to reality

Since the announcement, in May, of the selection of the sites – one in South Africa and the other in Australia – to host the €1.5-billion international Square Kilometre Array (SKA) project (with the major part of the instrument to be in South Africa, in the Karoo region), developments have begun to accelerate.

“We now have a real project,” enthuses SKA South Africa (SKA SA) associate director for science and engineering Professor Justin Jonas. “A real project in which we can now see some real progress towards, certainly, the establishment of SKA Phase I.”

The international SKA project is run by the SKA Organisation (formally set up in December last year), which recently moved into its new head office building at Britain’s renowned Jodrell Bank radio astronomy observatory and which is headed by its director-general (DG), Professor Philip Diamond, who is British but has worked in Australia, Germany, Sweden and the US as well as the UK, and who was appointed in September (replacing Dr Michiel van Haarlem of the Netherlands who served as an interim DG). The project in South Africa is the responsibility of a separate, local organisation, SKA SA, which is also responsible for related local and complementary regional projects, and which is headed by its director, Dr Bernie Fanaroff.

As far as radio astronomy in South Africa is concerned, there is a relatively newly established SKA SA as well as the much older Hartebeesthoek Radio Astronomy Observatory (HartRAO), west of Pretoria. The future institutional relationship between SKA SA and HartRAO, and between the country’s radio and optical astronomy agencies (the latter being the South African Astronomical Observatory) is under consideration.

SKA SA’s local projects, related to, but originally separate from, the SKA, are KAT-7 and MeerKAT. (The complementary regional project is the African Very Long Baseline Interferometry – VLBI – Network, or AVN.) KAT-7 was originally intended as an engineering prototype and technology demonstrator, doing only limited science as a means to check the success of the dish design and materials, but it has proved such a success that it has become a working scientific instrument. MeerKAT was always intended as a precursor to the SKA and, in due course, will be incorporated within SKA Phase I.

Top KAT
KAT-7 comprises seven dishes (hence the derivation of the instrument’s name: Karoo Array Telescope – 7 [dishes]). Each of these dishes has a diameter of 12 m, and all are made from composites. The instrument is located some 80 km north west of the small town of Carnarvon in the Northern Cape province, in the midst of a legally defined and enforced radio astronomy reserve, to reduce radio frequency interference to an absolute minimum. This area will also host MeerKAT and the core of SKA Phase I.

The use of composites to manufacture radio telescope dishes has been separately pioneered by South Africa and Canada. In South Africa, the idea was first tried out with a single, 15 m diameter, prototype dish, which was erected at HartRAO and originally called the XDM (for eXperimental Demonstrator Model). This, too, is now an operational scientific instrument, used mainly for pulsar and VLBI research and now known – following international radio astronomy tradition – simply as the HartRAO 15 m dish. (A pulsar is a rapidly spinning neutron star which emits beams of radiation, which sweep across the line of sight of earthly observers in a very regular period.)

All the KAT-7 dishes were designed and built in South Africa, and the composite materials they employ were tested by the Mechanical Testing Laboratory of the Council for Scientific and Industrial Research, in Pretoria, to ensure that the material was suitable for radio astronomy dish purposes. “KAT-7 should have a size-able scientific programme next year,” reports Jonas. “What we’re already doing with it is research into radio transient sources.”

(Radio transients, which include pulsars, are a wide range of celestial objects which emit bursts of radio waves.)

“In the future, we will also be looking for neutral hydrogen, associated with distant galaxies, and we will have a programme to monitor pulsars. These will all be international programmes. Scientists who will be involved with MeerKAT will be doing early work on KAT-7, testing out their systems.”

The current radio transient programme is headed by Dr Robert Fender of the University of Southampton, in the UK, who also works part-time at the University of Cape Town. The researchers into neutral hydrogen are already formed into the MeerKAT Hydrogen Team, which has members in Australia, Europe, South Africa, the US and other countries. The pulsar research programme will also involve a large, broadly based team, from all South African institutions and universities involved in radio astronomy, and from overseas institutions, mainly from Australia, Germany and the UK, but also some from the US.

Bigger & Better
“MeerKAT is a project with a huge scope,” highlights MeerKAT project manager Willem Esterhuyse. “It will be the most sensitive radio telescope in its frequency range in the world. We’re confident that it’ll be even more sensitive than was originally specified as a result of optimisation and best practice implementation, without increasing the budget. Only the SKA will be more sensitive.”

The name MeerKAT is a play on words – in Afrikaans, “meer” is the word for more, so MeerKAT = MoreKAT; but Meerkat is also the name of a highly social Southern African mammal (the Karoo is one of its haunts) known for always having at least one member of each group on high alert for possible danger. Sharp-eared, sharp-eyed and always found in groups, they form an ideal symbol or mascot for a South African-based radio telescope array.

“The MeerKAT project is running on schedule and on budget and we aim to ensure that remains the case. Next year we will have completed most of the infrastructure on the site,” he reports.

“We will be putting a lot of design effort into the dishes, the tooling needed to build them, and also the qualification of the different components. We’re very much in the development phase for the systems and subsystems. We will have a prototype receiver and we will also be doing prototyping of subsystems. More software will be rolled out, using KAT-7 as a test-bed.” Much of the software for KAT-7 and MeerKAT has been and will be developed and written in South Africa.

MeerKAT will be composed of 64 dishes. “We’re reaching a very advanced stage in the design of the dishes, with Stratosat Datacom – the South African lead contractor – and its technology partner, General Dynamics Satcom, in the US, (which includes Vertex Antennas in Germany),” states Jonas.

“Establishment of the site for the first dish should start in September next year, with the first dish installation in early 2014,” says Esterhuyse.

This first dish will then be subjected to engineering tests, to prove that it can function properly as a machine, such as rotating in elevation and azimuth as and at the pointing accuracy desired. Then it will be fitted with its receiver, signal path and digitiser. (The dish collects radio waves and focuses them on the receiver; the radio waves are then carried in analogue form by the signal path to the digitiser, which converts them into digital format. In the completed array, the digital signals from all the dishes will be combined, processed and analysed to produce the data sought by the astronomers.)

Once the dish has been completely fitted out, the full system will be qualified. This will include the collection of some astronomical data, to establish that it is working properly. Thus, the commissioning of the dish has two aspects: engineering commissioning and scientific commissioning.

Thereafter, there will be some industrialisation work for the subsequent dishes. By the end of 2014, four or five dishes should have been erected, by the end of 2015 this should have risen to 32 and by the end of 2016, all 64 should have been set up and have gone through engineering commissioning and 32 will have passed scientific commissioning. MeerKAT will become fully operational once scientific commissioning has been completed, by late 2017.

While the first MeerKAT dish may not be manufactured in South Africa, all the 63 others most certainly will be, although the manufacturers have not yet been selected. The assembly and integration of the antennas will take place in dedicated facilities currently being erected at the MeerKAT site in the Karoo. One facility will be dedicated to the assembly and integration of the pedestals and another will do the same for the dishes.

The pedestal and dish assemblies will then be transported separately to the relevant foundations for final erection and integration. “This allows quicker and more comprehensive integration in a pleasant working environment,” explains Esterhuyse. “This helps ensure that the final performance of the antenna will meet the specifications.”

The MeerKAT dishes will differ from the KAT-7 dishes in a number of ways. The MeerKAT dishes will be bigger, with a projected diameter of 13.5 m each. They will have a different layout, using a Gregorian offset design (with a primary reflector focusing the radio waves on to a smaller concave secondary reflector, offset to one side of the dish, which then focuses them on to the receiver). The Gregorian offset design provides an unobstructed path for the radio waves from space, through the reflectors, to the receiver.

The KAT-7 antennas have prime focus configurations – they have receivers, mounted on supporting legs, above the centre of the dishes. Among other issues, these legs cause scattering of the incoming radio waves, so they have to be as thin as possible, which reduces the weight they can bear, which means that they cannot easily accommodate multiple feeds for various frequencies mounted in a cluster on the dish, and there are severe restrictions on the weight of the electronics that can be mounted at the focal point (where the receiver is).

Despite all the work done with the HartRAO 15 m dish and the KAT-7 dishes, the MeerKAT dishes will be made from metal, not from composites. A comprehensive tender process was followed for the MeerKAT and the result was that the best value for money option at the time was selected. Both the composite and metal dishes tendered for the project met the performance specifications. “We prescribed performance, not materials,” elucidates Esterhuyse. “So, the solution could utilise aluminium, composites, whatever – as long as the performance was met.” Coincidently, the rigorous technical evaluation also concluded that the metal dishes had superior performance to the composite dishes.

“Stratosat is a South African company, and 75% local content is a contractual con-dition,” highlights Esterhuyse. “SKA SA will own all IP [intellectual property] (and background IP to use the IP that is created) on this project – we can therefore build more of these dishes if we want. So we have not conceded local content.”

Nor has SKA SA abandoned the concept of composite dishes. “We still believe composites are a feasible technology and will be talking to the Canadians on collaboration – they have a similar concept,” he assures. These talks, on aligning the South African and Canadian efforts, will start next month (December). The intent is to involve the South African companies that developed the composite dishes for HartRAO and KAT-7, namely MMS and the Dynamics division of BAE Systems Land Systems South Africa.

Universe Probe
The SKA will be the largest and most sensitive radio telescope ever built, providing, when Phase II is finished, a collecting area of about a million square metres (or a square kilometre, hence its name). It will allow astronomers to go far deeper into space, and so far further back in time, than is now possible, and play a major role in deter- mining how the universe has evolved.

The SKA is no longer just a concept but has now moved into its preconstruction phase.

SKA Phase I will add 250 dishes to the 64 dishes of MeerKAT and the 36 dishes of ASKAP (Australian SKA Precursor – the last of its dishes was completed in early October and this instrument is now under- going scientific commissioning. Each ASKAP dish is 12 m in diameter and made of metal). Of the SKA Phase I dishes, 190 will be in the Karoo and 60 in Western Australia.

“Our existing infrastructure on site in the Karoo will be sufficient for the mid-frequency dish component of SKA Phase I,” affirms Jonas. “We will have enough power and data connections, which will reduce the start-up cost of the SKA significantly. This infrastructure will form part of our contribution to the SKA.” The current schedule is for the preconstruction phase to result in con- struction readiness by the end of 2015.

The SKA Organisation’s engineering team visited the South African SKA site in September and its Australian counterpart in October, and met with the local engineering and management teams in both countries.

“The information they gathered over the course of their visits to the sites will be used to help develop detailed implementation plans for the integration of the ASKAP and MeerKAT precursor telescopes, and associated infrastructure, into Phase I of the SKA,” explains SKA Organisation interim outreach officer Jo Bowler.

“The development of these implementation plans, along with the detailed design of all elements of the SKA system, will be carried out during the preconstruction phase that the project has now entered.”

The formal negotiations between the SKA board and South Africa and Australia to develop the details of the SKA hosting agreements with both countries will start in the near future. “This will be a complex process, covering in detail, all areas necessary to establish an international megascience facility in the two host countries,” she points out.

In addition, the SKA Organisation plans to conclude agreements with a small number of consortia who will be responsible for the work packages that will account for a large part of the engineering work for each element that will make up the SKA system. “A request for expressions of interest for involvement in stage one of the preconstruction phase work packages was issued earlier this year,” she reports. “The SKA office has received a high level of interest from potential participants. A formal request for proposals will be issued early in 2013.”

Furthermore, in the near future the SKA Organisation will recruit some 60 scientists, engineers and support staff to join its existing personnel and bring it up to its intended complement for the preconstruction phase. Construction of SKA Phase I is planned to start in 2016 and full science operation should commence in 2020. Phase II con-struction should also start in 2020 and be finished in 2024.