The SKA Africa Radio Antenna Positioner was the Overall Winner at South Africa’s Steel Awards 2015. It was also the winner of the Association of Steel Tube and Pipe Manufacturers (ASTPM) tubular category. This is the second year in a row that the overall winner comes from this category.
The judges said that this project “radiates excellence not only in the use of structural steel but in every aspect of its structure and purpose.”
The SKA (Square Kilometre Array) project is an international effort to build the world’s largest radio telescope collecting area. When operational, the SKA will provide astronomers unprecedented detail, thousands of times faster than currently and to a resolution 50 times that of the Hubble Space Telescope.
Part of South Africa’s technical capability displayed in the bid for the SKA was backed up by the design and build of the seven dishes for the SKA Africa Telescope. This ‘mini-SKA’ has in itself displayed excellence, delivering images of the galaxy Centaurus A, 13-million light years away.
The SKA Africa programme is for 64 antenna positioners to be completed by late 2016, on a site 90 kilometres from Carnarvon, Northern Cape without mobile phone contact, far from engineering resources, so that by mid-2017 the SKA will be doing scientific work.
The antenna framework is mounted on a T-shaped yoke, fabricated from thick plates which are connected to the pedestal by means of axles fitted into line bored holes and bearings. The height is 19.5 metres and the mass 42 tons.
The judges noted that the enormous complexity of the geometry for the antennae “must surely compete with last year’s overall winner, the Malapa project which was complex but was built with the luxury of “our normal” two millimetre structural tolerances.”
Prevention of distortion from welding to the yoke is just one of the many challenges faced by the fabrication team and the judges said: “This was excellent use of plated steelwork highlighting the versatility of the fabricators repertoire.”
The antennae positioner allows for a vertical (tilt)range of 15° to 88°, and an azimuth range of 360° to an accuracy of within 1.4 thousandths of a degree under optimal conditions and 7 thousandths of a degree during normal operational conditions. “That’s a degree of accuracy that is hard to grasp for structural engineers given the fact that we normally work to the nearest 2 millimetres,” the judges said.
The largely tubular antennae support structure, was, by choice of the fabrication team, built with zero tolerance targets. “The engineering, detailing, jig fabrication and construction put these structures into a different league from your run-of-the-mill tubular truss type project. The accuracy of dimensions after erection is critical to give the radio telescope maximum chance of achieving its unimaginable expected accuracy,” the judges said.
“A scientific project of this nature that taxes the skills of South African engineers and scientists to rise above the challenges and make it work, represents excellence in every way, but it is especially a triumph in the use of steelwork and is truly deserving of being the Overall Winner of Steel Awards 2015,” the judges concluded.
Client / Developer: SKA Africa
Main Contractor/ Project Manager: General Dynamics SATCOM technologies
Structural Engineer: General Dynamics SATCOM Technologies, Vertex Antennas (Germany)
Steelwork Contractors: Tricom Structures
BUS structure: Tricom Structures (a subsidiary of Robor)
Pedestal: Efficient Engineering
Structural Steel Detailer/ Detailing Company: Tricom Structures (a subsidiary of Robor)
Painting: Joesa Painting