Sometime in the mid-2020s, the Square Kilometer Array (SKA) telescope is expected to deliver its first science data. When completed, it will be the largest scientific instrument ever built, spanning thousands of kilometres and two continents. It is expected to collect so much data that entirely new computer technologies will need to be invented to process it all. But for some, the greatest benefit will not be the science questions that it answers, but the investments in countries across Africa that are required to build it in the first place. The supporting infrastructure alone will provide new roads, electricity and Internet access to millions of people for the first time, and thousands of local engineers and technicians will be trained and directly involved in creating brand new technologies that are essential for the project’s success.
The SKA is going to be the world’s most sensitive radio telescope, able to observe the universe in fine details across multiple wavelengths. The name comes from the total collecting area of one square kilometre, but rather than try to create a single enormous dish, the designers opted to construct a vast array of thousands of smaller dishes and antennae. The different types of receiver will be sensitive to different radio bands, with some listening to the low frequencies commonly used by commercial radio and television stations, and others looking in higher frequency microwave bands. The different bands reveal different aspects of the universe, in a similar way to how infrared cameras reveal a different view of the world to colour cameras that see visible light.
But ultra-large radio telescopes already exist, like the 305 meter Arecibo telescope in Puerto Rico, or the 500meter FAST telescope in Guizhou, China. Their telescopes are the current sensitivity champions, in their given bands, but they do have certain limitations. For starters, a radio dish has to hold a very precise shape for it to work, and the only way to build such enormous dishes is to bury them in the ground. Both Arecibo and FAST were built in natural depressions in the ground, and are fixed in place – they are aimed by waiting for the Earth’s rotation to point them in roughly the right direction. They also have limited resolution – radio waves do not focus as finely as visible light, so radio telescopes need to be many thousands of times wider than their optical equivalents to achieve the same sharpness.
Fortunately, it is possible to improve a radio telescope’s aperture by dividing it into many smaller receivers, which can then be distributed as widely as needed. Their signals are then combined through a process called “baseline interferometry” to synthesize an image as if it were created by a single telescope as wide as the distance between the actual receivers. One of the largest examples of this is the Event Horizon Telescope, an array assembled from radio telescopes all over the Earth, to synthesize a virtual telescope the size of the entire planet. SKA will not have as wide a baseline as this, but the higher density of receivers, the enormous total surface area, and the wide range of bands in which it can see will make it the most powerful radio telescope ever built.
The original SKA design called for a single array, to be built in a suitable location. The area needed to be radio-quiet, meaning that it had to be relatively unpopulated, and the search for a home eventually came down to a decision between the Karoo in South Africa, and a remote region in Western Australia. Both countries made strong cases for being the host country, so the decision was eventually made to divide the array by function, with the low-frequency parts being built in Australia, and the remainder being built in Southern Africa. Dividing the telescope like this adds to the logistical and infrastructure challenges of its construction, but adds the advantage of allowing it to observe the same target for almost 24 hours at a time – as the Earth rotates and a target sets below the horizon in Australia, it becomes visible in Africa, and the telescope can continue observing.
The Australian site is in Murchison, near the western coast of Australia and several hundred kilometres north of Perth. The African site is centred near Carnarvon in the Northern Cape province of South Africa, extending into Botswana, Ghana, Kenya, Madagascar, Mauritius, Mozambique, Namibia and Zambia.
The central portion of the SKA’s African site will be built 90km from Carnarvon, a small Karoo town supporting local sheep farmers. Carnarvon, and other towns in the region, have already benefited from infrastructure improvements needed to build the SKA, such as improved roads, more reliable electricity, and access to very high-speed broadband Internet.
However, Not all locals are embracing the project. Many farmers are concerned that the large amounts of land which have been purchased by the SKA and which are no longer available for farming will impact their livelihoods. And the Astronomy Geographic Act, which allows the government to place restrictions on radio broadcast activity within a certain range of radio telescope equipment, is also a matter of concern for the widely distributed population who rely on the radio spectrum in their daily lives.
For this reason, SKA management realises how important it is to build strong relationships with the local communities living in the area where the dishes will be built, and are making a concerted effort to provide jobs and education to local residents. Schools have been upgraded with modern computer centres, Bursaries have been awarded to local students studying science and engineering, and over R420 million (about USD 29 million) has been invested in the region so far.
Although the final design of the SKA is still being completed, it is already returning groundbreaking science data. As part of their bids to host the SKA, both South Africa and Australia built precursor telescopes to demonstrate their ability to complete such a large and sophisticated engineering project. South Africa built the eight dish Karoo Array Telescope (KAT), later upgraded to the 32 dish MeerKAT telescope, and Australia built the Australian SKA Pathfinder (ASKAP) telescope. Both will eventually be incorporated into the full SKA telescope. Although each has only a small fraction of the eventual power of the finished telescope, they are world-leading instruments which are already revealing aspects of our galaxy which had never been seen before.
And when the final phase of construction is completed and the SKA is fully operational? History shows that while the project has a well-defined list of science goals, the real benefit will come from new discoveries in areas that could not have been anticipated. And the host countries will reap the practical benefits of having contributed to the development of the entirely new technologies underpinning the telescope itself, for decades to come.