Antennas integral to Square Kilometre Array (SKA) telescope
The design for the MeerKAT antenna positioner was finalised after a year of technical collaboration between Stratosat Datacom (SD) / General Dynamics Satcom Technologies and SKA South Africa.
The vendor selection process came to an end after months of intense vendor and fabricator vetting, which resulted in Stratosat Datacom issuing contracts to major subcontractors for the multitude of components and fabricated items that will make up the 41-ton, five story high precision telescope.
The antenna positioner will be a truly South African-built initiative. Due to the unique 13.5 metre offset Gregorian design, careful consideration was taken in selecting South African fabricators that would not only be able to deliver high quality parts and components, but also sustain a production schedule that will allow the project to maintain the required delivery and installation schedule.
At least 75% of the components making up the MeerKAT antennas will be manufactured in South Africa, but several industries in SKA Organisation partner countries around the world are also making crucial contributions. The global technology collaborations are bringing cutting-edge know-how and many years of antenna experience to the MeerKAT project, and are designed to transfer expertise to the South African industry partners. For example, the first set of reflector panels, as well as the first receiver indexer and sub-reflector were manufactured abroad, but the remainder of these will be made locally.
The full MeerKAT array will consist of 64 identical receptors (antennas with receivers, digitisers and other electronics installed). Connected by 170 km of underground fibre optic cable, the 64 receptors will operate as a single, highly sensitive astronomical instrument, controlled and monitored remotely from the MeerKAT control room in Cape Town.
MeerKAT’s 64 antenna foundations, consisting of close to 5 000 m³ of concrete and more than 570 tons of steel, were completed over a period of seven months, with the final foundation poured on 11 February 2014.
TSR were contracted to supply the majority of the slew rings for the antennas. Initially the SKA Organisation contracted a company in Germany and TSW to supply one slew ring each. You could say they were ‘testing the waters’ with TSW, but after viewing what TSW could manufacture, with the quality and precision that they needed, TSW were awarded the rest of the contract. This consists of the remaining 62 slew rings and the associated engineering components.
The backbone of the antenna positioner is a 25-ton backup structure that consists of 6 000 different components that have to be perfectly aligned to ensure the structure can accommodate the highly accurate and sensitive reflector panels for MeerKAT. Tricom Structures was selected as the fabricator and after months of design meetings, the trial assembly of the first backup structure was successfully completed in Pretoria.
The pedestal and yoke are connected by the high precision, low tolerance azimuth bearings (slew rings). Considering the lifetime requirements of the antenna positioners and the amount of slew and tracking movements the telescope will perform on a daily basis, SD engaged with a bearing supplier that can deliver a slew ring that meets these stringent requirements.
Efficient Engineering awarded contract
The pedestal and yoke section of the antenna positioner was awarded to Efficient Engineering. Their extensive experience in heavy steel fabrication combined with their ability to provide the integration services of the pedestal, made Efficient Engineering the perfect subcontractor for these complex structures.
The company has been contracted to manufacture all 64 pedestal and yoke sections which is estimated to take a period of 36 months and needs to be completed by the end of 2016.
Predominantly S355 (300WA) plate material and some 304 stainless steel was used in the construction of the structures. Sub-arc welding of pedestal sections using column and boom, as well as GMAW (hand) and a large amount of CNC machining with very tight tolerances was needed.
Each pedestal and yoke section is eight metres tall and 2.5 metres wide at the base, and they weigh approximately 12 tons without the backup structure.
Astronomy teams from around the world have signed up to start using MeerKAT as soon as 16 of its receptors have been commissioned (around June 2015). The full array should be doing routine science observations by the end of 2017.
For further details contact Efficient Engineering on TEL: 011 928 4800 or visit www.efficient.co.za