Square Kilometre Array
|Square Kilometre Array (SKA)|
An artist's impression of the central core of dish antennas of the SKA
|Location||Australia / New Zealand / South Africa|
|Built||Phase 1 2020
Phase 2 2025
Phase 3 2025 onwards
|First light||2020 (planned)|
|Telescope style||Phased array|
|Collecting area||1,000,000 m²|
The Square Kilometre Array (SKA) is a radio telescope in development in Australia and South Africa which will have a total collecting area of approximately one square kilometre. It will operate over a wide range of frequencies and its size will make it 50 times more sensitive than any other radio instrument. It will require very high performance central computing engines and long-haul links with a capacity greater than the current global Internet traffic. It will be able to survey the sky more than ten thousand times faster than ever before.
With receiving stations extending out to distance of at least 3,000 kilometres (1,900 mi) from a concentrated central core, it will exploit radio astronomy's ability to provide the highest resolution images in all astronomy. The SKA will be built in the southern hemisphere, in Sub-Saharan states with cores in South Africa and Australia, where the view of the Milky Way Galaxy is best and radio interference least.
With a budget of about €1.5 billion, construction of the SKA is scheduled to begin in 2018 for initial observations by 2020 and full operation by 2025. The headquarters of the project are in Manchester, in the UK.
- 1 Organisation
- 2 Description
- 3 Key projects
- 4 Locations
- 5 Precursors, pathfinders and design studies
- 6 Timeline and funding
- 7 Project risks
- 8 See also
- 9 References
- 10 External links
In November 2011, the SKA Organisation was formed and the project moved from a collaboration to an independent, not for profit, company. As of December 2012[update], the members of the SKA Organisation are:
- Australia: Department of Innovation, Industry, Science and Research
- Canada: National Research Council
- China: National Astronomical Observatories of the Chinese Academy of Sciences
- Germany: Federal Ministry of Education and Research (withdrew in 2014.)
- Italy: National Institute for Astrophysics
- New Zealand: Ministry of Economic Development
- South Africa: National Research Foundation
- Sweden: Onsala Space Observatory
- The Netherlands: Netherlands Organisation for Scientific Research
- United Kingdom: Science and Technology Facilities Council
India's National Centre for Radio Astrophysics is an associate member of SKA. Germany is a member, but on 5 June 2014 the federal science ministry indicated its intention to leave the SKA project at the end of June 2015.
|This section does not cite any references or sources. (October 2012)|
The SKA will combine the signals received from thousands of small antennas spread over a distance of more than 3000 km to simulate a single giant radio telescope capable of extremely high sensitivity and angular resolution. The SKA will also have a very large field-of-view (FOV) with a goal at frequencies below 1 GHz of 200 square degrees and of more than 1 square degree (about 5 full Moons) at higher frequencies. One innovative development is the use of Focal Plane Arrays using phased-array technology to provide multiple FOVs. This will greatly increase the survey speed of the SKA and enable multiple users to observe different pieces of the sky simultaneously. The combination of a very large FOV with high sensitivity means that the SKA will transform the exploration of the Universe.
The SKA will provide continuous frequency coverage from 50 MHz to 14 GHz in the first two phases of its construction. A third phase will then extend the frequency range up to 30 GHz.
- Phase 1: Providing ~10% of the total collecting area at low and mid frequencies by 2020.
- Phase 2: Completion of the full array at low and mid frequencies by 2025.
The frequency range from 50 MHz to 14 GHz, spanning more than two decades, cannot be realised using one design of antenna and so the SKA will comprise arrays of three types of antenna elements that will make up the SKA-low, SKA-mid and dish arrays:
- SKA-low array – a phased array of simple dipole antennas to cover the frequency range from 50 to 350 MHz. These will be grouped in 100 m diameter stations each containing about 90 elements.
- SKA-mid array – an array several thousand dish antennas to cover the frequency range 350 MHz to 14 GHz. It is expected that the antenna design will follow that of the Allen Telescope Array using an offset Gregorian design having a height of 15 metres and a width of 12 metres.
- SKA-survey array - a compact array of parabolic dishes of 12–15 meters diameter each for the medium-frequency range, each equipped with a multi-beam, phased array feed with a huge field of view and several receiving systems covering about 350 MHz – 4 GHz. This allows the dishes to observe over a far wider field of view than that achieved with a single element feed. Prototypes of such multiple element feeds are now under development for the pathfinder arrays described below.
The area covered by the SKA – extending out to ~3000 km – will comprise three regions:
- A central region containing about 5 km diameter cores of SKA-mid antennas (South Africa) and of SKA-survey antennas and SKA-low dipoles (Western Australia). These central regions will contain approximately half of the total collecting area of the three SKA arrays.
- A mid region extending out to 180 km. This will contain dishes and pairs of SKA-mid and SKA-low stations. In each case they will be randomly placed within the area with the density of dishes and stations falling off towards the outer part of the region.
- An outer region from 180 km to 3000 km. This will comprise five spiral arms along which dishes of SKA-mid, grouped into stations of 20 dishes, will be located. The separation of the stations increases towards the outer ends of the spiral arms.
|This section needs additional citations for verification. (May 2012)|
The capabilities of the SKA will be designed to address a wide range of questions in astrophysics, fundamental physics, cosmology and particle astrophysics as well as extending the range of the observable universe.
A number of key science projects have been selected to be undertaken by the SKA and are listed below.
Extreme tests of general relativity
For almost one hundred years, Einstein's general theory of relativity has precisely predicted the outcome of every experiment made to test it. Most of these tests, including the most stringent ones, have been carried out using radio astronomical measurements. By using pulsars as cosmic gravitational wave detectors, or timing pulsars found orbiting black holes, astronomers will be able to examine the limits of general relativity such as the behaviour of space and time in regions of extremely curved space. The goal is to reveal whether Einstein was correct in his description of space, time and gravity, or whether alternatives to general relativity are needed to account for these phenomena.
Galaxies, cosmology, dark matter and dark energy
The sensitivity of the SKA in the 21-cm hydrogen line will map a billion galaxies out to the edge of the observable Universe. The large-scale structure of the cosmos revealed will give constraints to determine the processes resulting in galaxy formation and evolution. Imaging hydrogen through the Universe will provide a three-dimensional picture of the first ripples of structure which formed individual galaxies and clusters. This may also allow the measurement of effects hypothetically caused by dark energy and causing the increasing rate of expansion of the universe.
Epoch of re-ionization
The SKA is intended to provide observational data from the so-called Dark Ages (between 300,000 years after the Big Bang when the radiation stops and the universe cools) and the time of First Light (a billion years later when young galaxies are seen to form for the first time). By observing the primordial distribution of gas, the SKA should be able to see how the Universe gradually lit up as its stars and galaxies formed and then evolved. This period between the Dark Ages and First Light is considered the first chapter in the cosmic story of creation and the distance to see this event is the reason for the Square Kilometre Array's design. To see back to First Light requires a telescope 100 times more powerful than the biggest radio telescopes currently in the world, taking up 1 million square metres of collecting area, or one square kilometre.
It is still not possible to answer basic questions about the origin and evolution of cosmic magnetic fields, but it is clear that they are an important component of interstellar and intergalactic space. By mapping the effects of magnetism on the radiation from very distant galaxies, the SKA will investigate the form of cosmic magnetism and the role it has played in the evolving Universe.
Transient radio phenomena caused by extraterrestrial life
The SKA will be capable of detecting extremely weak extraterrestrial signals if existing, and may even detect planets capable of supporting life. Astrobiologists will use the SKA to search for amino acids by identifying spectral lines at specific frequencies.
Suitable sites for the SKA telescope need to be in unpopulated areas with guaranteed very low levels of man-made radio interference. Four sites were initially proposed in South Africa, Australia, Argentina and China. After considerable site evaluation surveys, Argentina and China were dropped and the other two sites were shortlisted (with New Zealand joining the Australian bid, and 8 other African countries joining the South African bid):
Australia and New Zealand: The core site is located at the Murchison Radio-astronomy Observatory (MRO) at Mileura Station near Boolardy in Western Australia 315 km north-east of Geraldton on a flat desert-like plain at an elevation of about 460 metres. The most distant stations will be located in New Zealand.
South Africa: The core site is located at Karoo area of the arid Northern Cape Province, about 75 km north-west of Carnarvon, with distant stations in Botswana, Ghana, Kenya, Madagascar, Mauritius, Mozambique, Namibia and Zambia.at an elevation of about 1000 metres in the
On 10 March 2012 it was reported that the SKA Site Advisory Committee had made a confidential report in February that the South African bid was stronger. The final decision on the site to be made by the project's board of directors was expected on 4 April 2012. However a scientific working group was set up to explore possible implementation options of the two candidate host regions, and its report was expected in mid May 2012.
On 25 May 2012 it was announced that the SKA will be split over the South African and African sites and the Australia and New Zealand sites. While New Zealand remains a member of the SKA Organisation, as of 2014[update] it appears that no SKA infrastructure is likely to be sited in New Zealand.
Precursors, pathfinders and design studies
Many groups are working globally to develop the technology and techniques required for the SKA. Their contributions to the international SKA project are classified as either: Precursors, Pathfinders or Design Studies.
- Precursor facility: A telescope on one of the two SKA candidate sites, carrying out SKA-related activity.
- Pathfinder: A telescope or programme carrying out SKA-related technology, science and operations activity.
- Design Study: A study of one or more major sub-systems of the SKA design, including the construction of prototypes
Australian SKA Pathfinder (ASKAP)
The Australian SKA Pathfinder, or ASKAP, is an A$100 million project to build a telescope array of thirty-six twelve-metre dishes. It will employ advanced, innovative technologies such as phased array feeds to give a wide field of view (30 square degrees).
ASKAP is being built by CSIRO at the Murchison Radio-astronomy Observatory site, located near Boolardy in the Mid West region of Western Australia. All 36 antennas and their technical systems were officially opened in October 2012.
MeerKAT is a South African project to build an array of sixty-four 13.5-metre diameter dishes as a world class science instrument and also to enable technology required for the SKA to be developed. KAT-7, a seven-dish engineering and science testbed instrument for MeerKAT, located near Carnarvon in the Northern Cape Province of South Africa is already up and running and the full MeerKAT array is expected to be ready by 2015–2016. The dishes will be equipped with a number of high performance single pixel feeds to cover frequencies from 580 MHz up to 14 GHz.
Murchison Widefield Array (MWA)
The Murchison Widefield Array is a low-frequency radio array operating in the frequency range 80–300 MHz also under construction at the Murchison Radio-astronomy Observatory site in Western Australia.
- APERture Tile In Focus (Apertif)
- Very Long Baseline Interferometry
- Electronic MultiBeam Radio Astronomy ConcEpt
- Expanded Very Large Array
- Long Wavelength Array
- SKA Molonglo Prototype
Allen Telescope Array
The Allen Telescope Array uses innovative 6.1m offset Gregorian dishes equipped with wide band single feeds covering frequencies from 500 MHz to 11 GHz. The 42-element array now in operation is to be extended to 350 elements. The dish design has explored methods of low-cost manufacture.
LOFAR is a €150 million Dutch-led project building a novel low frequency phased aperture arrays spread over northern Europe. An all-electronic telescope covering low frequencies from 10 to 240 MHz which has been coming online through 2009 to 2011. LOFAR is currently developing crucial processing techniques vital to the SKA.
|Data challenges of SKA pathfinders|
budgeted for ASKAP
Requirements for the SKA itself are about 100 times greater.
|Large bandwidth from
telescope to processor
|~10 Tb/s from antennas to correlator (< 6 km)
40 Gb/s from correlator to processor (~ 600 km)
|Large processing power||750 Tflop/s expected/budgeted
1 Pflop desired
|1 MW at site
10 MW for processor
|including data validation, source extraction,
|Storage and duration
|70 PB/yr if all products are kept
5 PB/yr with current funding
8 h to write 12 h of data to disk at 10GB/s
|Retrieval of data
|all data in public domain
accessed using VO tools & services
|Data-intensive research||data mining, stacking,
- Aperture Array Verification Programme
- Canadian SKA Program
- Preparatory Study for the SKA
The amount of sensory information collected pose a huge problem in storing and require real-time signal processing to reduce the information to relevant data.
Technology Development Project (TDP)
The Technology Development Project, or TDP, is a US$12 million project to specifically develop dish and feed technology for the SKA. It is operated by a consortium of universities led by Cornell University and was completed in 2012.
Timeline and funding
The SKA was originally conceived in 1991 with an international working group set up in 1993. This led to the signing of the first Memorandum of Agreement in 2000. Considerable early development work then followed. This culminated in the commencement of PrepSKA in 2008 leading to a full SKA design in 2012. Construction of Phase 1 will take place from 2018 to 2020 providing an operational array capable of carrying out the first science. Phase 2 will then follow for completion in 2025 providing full sensitivity for frequencies up to at least 14 GHz.
The SKA is projected to cost €2 billion, this includes €650 million for Phase 1 completing 2020. The funding will come from many international funding agencies. The SKA and the European Extremely Large Telescope (E-ELT) are the two flagship facilities for ground-based astronomy in the future. They are equal high priority projects in the ASTRONET roadmap for European astronomy.
Potential risks for priority astronomical sites in South Africa are protected by the Astronomy Geographic Advantage Act of 2007. Put in place to specifically support the South African SKA bid, it outlaws all activities that could endanger scientific operation of core astronomical instruments. In 2010, concerns were raised over the will to enforce this law when Royal Dutch Shell applied to explore the Karoo for shale gas using hydraulic fracturing, an activity that would have the potential to increase radio interference at the site.
An identified remote station location for the southern African array in Mozambique was subject to flooding and excluded from the project, despite the SKA Site Selection Committee technical analysis reporting that all African remote stations could implement flood mitigation solutions.
Australia's first Radio Quiet Zone (RQZ) was established by the Australian Communications and Media Authority (ACMA) on 11 April 2005 specifically to protect and maintain the current ‘radio-quietness’ of the main Australian SKA site at the Murchison Radio-astronomy Observatory.
In February 2012, a former Australian SKA Committee chairman raised concerns with South African media about risks at the Australian candidate site, particularly in terms of cost, mining interference and land agreements. SKA Australia stated that all points had been addressed in the site bid.
- List of radio telescopes
- LOFAR (the Low Frequency Array, currently under construction in several European countries, with its core in the Netherlands)
- Mills Cross (historical connections with the SKA development in Australia)
- Project Cyclops
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- EMBRACE website
- e-MERLIN website
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- SKAMP website
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- LOFAR website
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- AAVP website
- Canadian SKA Program website
- PREPSKA website
- SKATDP website
- Nordling, Linda (22 March 2011). "Mining plans pose threat to South African astronomy site". Nature. Retrieved 27 June 2011.
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|Wikimedia Commons has media related to Square Kilometre Array.|
- SKA Australia web site
- "Inside the Square Kilometre Array", Cosmos magazine online, January 2012
- "The Square Kilometre Array Category", The Conversation, 2011/12
- "Australian SKA Planning Office Newsletter" (PDF). CSIRO. 10 April 2007. Retrieved 19 March 2007.
- Boolardy Station and the Murchison Radio-Astronomy Observatory (MRO) – University of Western Australia
- Photographs from the Boolardy site, June 2010
- South Africa
- Merrifield, Michael; Crowther, Paul. "Where to Build The Square Kilometre Array?". Deep Space Videos. Brady Haran.