SKA selects the final design of the SKA dish

The Square Kilometre Array (SKA) Project has selected the design for its dish, opening up the way for the eventual production of hundreds of dishes that will make up the world’s largest radio telescope.

“This decision is a major milestone towards delivering the SKA,” said Alistair McPherson, Head of Project at SKA Organisation. “Being able to “see” what the SKA dishes will look like for the first time is a big satisfaction for all involved.”

Three antenna concepts were built to be considered for the design of the SKA dish: DVA-1 in Canada, DVA-C in China, and MeerKAT-1 in South Africa. All three were constructed using different technology from the different partners, representing the very best in radio telescope dish technology currently available.

The consortium then presented the following designs for study:
An innovative Single Skin, Rim supported Composite (SRC) concept led by the National Research Council of Canada (NRC), along with SED Systems of Canada and RPC Composites of Australia.
An optimised Panel, Space-frame supported Metal (PSM) concept, led by a Shijiazhuang, China based team composed of JLRAT/CETC-54 along with their European partner, MT Mechatronics (MTM) of Mainz, Germany.


An artist impression of the full SKA at night, with the selected Panel Space-frame supported Metal (PSM) SKA dish design in the foreground

A five-strong selection panel of engineering experts in the fields of composites, radio telescope antennas and systems engineering assessed both designs on a series of indicators including surface accuracy, feasibility of on-site manufacturing and ability to maintain structural integrity over long time-frames and made a unanimous recommendation that the Chinese PSM concept should be selected for the SKA dishes, a recommendation that was then approved by the SKA Dish Consortium Board.

The SKA Dish Consortium, made up of institutes from Australia (who leads the consortium), Canada, China, Germany, Italy and South Africa is responsible for the design and verification of the dish that will make up SKA-mid, one of two SKA instruments. In its first phase of deployment (SKA1), SKA-mid will be initially composed of 133 15-metre diameter dishes providing a continuous coverage from 350 MHz to 14 GHz.

One of the greatest challenges faced by the consortium is the mass production of hundreds of these dishes, all with identical performance characteristics, and built to last and tolerate the harsh conditions of the remote arid areas in which they will operate for 50 years. Combined with achieving a large high precision collecting area at a competitive price, it’s a formidable technical and engineering challenge.

“We’re confident the selected design will perform well in the harsh conditions of the Karoo in South Africa and will deliver the precision that the scientific community needs to answer the questions they’re trying to solve,” said Roger Franzen, SKA Dish Consortium Lead.

“The next step for us is to build and test a prototype at the South African site,” he continued.

The detailed design and manufacturing of such prototype, called SKA-P, is led by JLRAT/CETC54 in collaboration with the European companies MTM and Società Aerospaziale Mediterranea (SAM), and the Assembly, Integration and Verification of SKA-P will be done on site together with the SKA SA team.

“We expect the installation of SKA-P on the ground to happen by spring 2017,” said Roger Franzen. “Once satisfied with its performance, the project will be in a good position to go to tender and issue the contract for the mass production of 133 dishes to make up SKA1-mid.”

Beyond the design of the dish structure, the consortium is also tasked with designing and testing optics, receivers and other elements of the dish. As part of that process, NRC continues its valuable contributions to single pixel feed (SPF) receivers/digitizers and cryogenic low noise amplifiers (LNAs).

The ambitious Square Kilometer Array (SKA) project has started to bear fruit. Despite being only a quarter of its final size, the MeerKAT radio telescope under construction in the Karoo region in South Africa has already delivered a fresh perspective on the cosmos. In May, with only four dishes, the MeerKAT produced a remarkable view of the sky, revealing never seen before radio galaxies in the distant universe.

In July 2016, using the16-dish MeerKAT, a new image of the radio sky showed more than 1 300 radio galaxies in the distant universe compared to 70 in the previous best image.

The antenna consists of the main reflector (effective diameter 13.5 metres) plus the sub-reflector (diameter 3.8 metres). The main reflector is made up of 40 panels, made of aluminium. The sub-reflector is a single piece composite structure. The total height of a MeerKAT antenna is 19.5 metres and weighs in at 42 tons.

MeerKAT is part of a much larger network: the Square Kilometer Array (SKA). This huge network will bring together another 133 dishes in South Africa as well as over 130 000 low-frequency antennas in Australia, enabling the universe to be scanned in unprecedented detail thousands of times faster than current technology.

Once MeerKAT is complete, construction on the remainder of the SKA is expected to begin in 2018.

Why MeerKAT?
The telescope was originally known as the Karoo Array Telescope (KAT) that would consist of 20 receptors. When the South African government increased the budget to allow the building of 64 receptors, the team re-named it “MeerKAT”, i.e. more of KAT. The meerkat is also a much beloved small mammal that lives in the Karoo and other regions in South Africa.

Key local suppliers include Efficient Engineering (pedestals and yokes), Titanus Slew Rings (azimuth bearing), Tricom Structures and Namaqua Engineering (back-up structure), Westarcor Engineering and General Profiling (receiver indexer) and Stratosat (reflectors).

The SKA is not a single telescope, but a collection of telescopes or instruments, called an array, to be spread over long distances. The SKA is to be constructed in two phases: Phase 1 (called SKA1) in South Africa and Australia; Phase 2 (called SKA2) expanding into other African countries, with the component in Australia also being expanded.