Square Kilometre Array

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Square Kilometre Array (SKA)
Artist impression of all four SKA instruments at night under one sky. In it are visible the SKA dishes with MeerKAT and ASKAP dishes in the background, as well as a station of the low frequency aperture array in the bottom right corner and a station of the mid frequency aperture array in the bottom left corner. The left half of the image represents the antennas to be located in Africa and the right half the ones to be located in Australia.
Location Australia / Africa
Built Phase 1 2018-2023
Phase 2 2023-2030
[1]
First light 2020 (planned)
Telescope style Phased array
Collecting area 1,000,000 m²
Website skatelescope.org

The Square Kilometre Array (SKA) is a radio telescope project to be built in Australia and South Africa which would have a total collecting area of approximately one square kilometre.[2][3] 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.[4] 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.[5]

Construction of the SKA is scheduled to begin in 2018 for initial observations by 2020, but the construction budget is not secured at this stage. The SKA will be built in two phases, with Phase 1 (2018-2023) representing about 10% of the capability of the whole telescope.[6][7] Phase 1 of the SKA was cost-capped at 650 million euros in 2013, while Phase 2's cost has not yet been established.[8] The headquarters of the project are located at the Jodrell Bank Observatory, in the UK.[9]

Organisation[edit]

The SKA is a global project with ten member countries which aims to provide answers to fundamental questions about the origin and evolution of the Universe.[10]

In April 2011, Jodrell Bank Observatory of the University of Manchester, in Cheshire, England was announced as the location of the headquarters office for the project.[11]

In November 2011, the SKA Organisation was formed and the project moved from a collaboration to an independent, not for profit, company.[12] As of August 2014, the members of the SKA Organisation are:[12][13][14]

Germany is a member,[17][18] but on 5 June 2014 the federal science ministry indicated its intention to leave the SKA project at the end of June 2015.[19]

Description[edit]

Countries which have participated in the preparatory phase of SKA[20]

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:

Artist's impression of a Low-Band SKA Sparse Aperture Array Station
Artist's impression of a SKA Dense Aperture Array Station
  1. 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.
  2. 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.
  3. 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:

  1. 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.
  2. 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.
  3. 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.

Key projects[edit]

Artist's impression of the Offset Gregorian Antennas
Schematic of the SKA Central Region

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[edit]

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[edit]

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.[21]

Epoch of re-ionization[edit]

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.[22]

Cosmic magnetism[edit]

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[edit]

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. SKA will be able to detect an airport radar within 50 light years.

Locations[edit]

The headquarters of the SKA will be located at Manchester's Jodrell Bank Observatory, Cheshire, England.[23]

An automatic wideband radio scanner system was used to survey the radio frequency noise levels at the various candidate sites in South Africa.

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.[24] 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[25][26] on a flat desert-like plain at an elevation of about 460 metres. The most distant stations will be located in New Zealand.[27]

South Africa: The core site is located at 30°43′16.068″S 21°24′40.06″E / 30.72113000°S 21.4111278°E / -30.72113000; 21.4111278 at an elevation of about 1000 metres in the 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.

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.[28] The final decision on the site to be made by the project's board of directors was expected on 4 April 2012.[28] 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.[29]

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.[5] While New Zealand remains a member of the SKA Organisation, as of 2014 it appears that no SKA infrastructure is likely to be sited in New Zealand.[30]

Precursors, pathfinders and design studies[edit]

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

Precursor facilities[edit]

CSIRO's ASKAP antennas at the MRO in Western Australia

Australian SKA Pathfinder (ASKAP)[edit]

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.[31]

MeerKAT[edit]

Main article: MeerKAT

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.[32]

Murchison Widefield Array (MWA)[edit]

The Murchison Widefield Array[33] 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.

Pathfinders[edit]

Allen Telescope Array[edit]

Main article: 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.[43]

LOFAR[edit]

Main article: LOFAR

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.[44]

Design studies[edit]

Data challenges of SKA pathfinders
Challenge Specifications[45]
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
Power consumption
of processors
1 MW at site
10 MW for processor
Pipeline processing
essential
including data validation, source extraction,
cross-identification, etc
Storage and duration
of data
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
by users
all data in public domain
accessed using VO tools & services
Data-intensive research data mining, stacking,
cross-correlation, etc.

Data challenges[edit]

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)[edit]

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.[49]

Timeline and funding[edit]

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,[15] 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.

Project risks[edit]

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.[50]

An identified remote station location for the southern African array in Mozambique was subject to flooding and excluded from the project,[51] despite the SKA Site Selection Committee technical analysis reporting that all African remote stations could implement flood mitigation solutions.[52]

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.[53]

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.[54]

During 2014, South Africa experienced month-long strike action by the National Union of Metalworkers (NUMSA), which added to the delays of the installation of dishes. The plan was to have six dishes operational by November, but only one MeerKAT dish stands on the Karoo site in the Northern Cape.[55]

The largest risk to the overall project is probably its budget which up until now has not been committed.[citation needed]

See also[edit]

References[edit]

  1. ^ "The project timeline". SKA Organisation. Retrieved 28 October 2014. 
  2. ^ "Facts and figures". SKA Organisation. Retrieved 26 May 2012. 
  3. ^ Spie (2014). "Philip Diamond plenary: The Square Kilometre Array: A Physics Machine for the 21st Century". SPIE Newsroom. doi:10.1117/2.3201407.12.  edit
  4. ^ [1], The Square Kilometre Array, p.24
  5. ^ a b "Africa and Australasia to share Square Kilometre Array". BBC. 25 May 2012. 
  6. ^ "The project timeline". SKA Organisation. Retrieved 28 October 2014. 
  7. ^ "SKA site bid outcome". SKA Africa. Retrieved 28 October 2014. 
  8. ^ "SKA Project". SKA Organisation. Retrieved 28 October 2014. 
  9. ^ "The SKA Organisation". SKA Organisation. Retrieved 28 October 2014. 
  10. ^ Redfern, Martin (31 March 2011). "World's biggest radio telescope, Square Kilometre Array". BBC News. Retrieved 2 April 2011. 
  11. ^ "Jodrell Bank chosen as base for largest radio telescope". BBC News. 2 April 2011. Retrieved 2 April 2011. 
  12. ^ a b "The organisation". SKA Organisation. 
  13. ^ http://www.mpifr-bonn.mpg.de/99606/news_publication_6728490?c=2169
  14. ^ "Sweden joins global radio telescope project". Chalmers. Retrieved 29 June 2012. 
  15. ^ a b Wild, Sarah (2014-06-09). "SKA upbeat, despite Germany's withdrawal". Mail & Guardian. Retrieved 2014-06-17. 
  16. ^ "India’s National Centre for Radio Astrophysics becomes the 11th full SKA Organisation member". SKA Organisation. Retrieved 11 August 2014. 
  17. ^ "Germany joins SKA, praises SA". Business Day. Retrieved 18 June 2012. 
  18. ^ "Deutschland beteiligt sich an SKA-Riesenteleskop". Welt Online. Retrieved 18 June 2012. 
  19. ^ William Garnier. "Germany announces its intent to leave the SKA Organisation". Square Kilometre Array. Retrieved 10 June 2014. 
  20. ^ "Participating countries". SKA Organisation. 
  21. ^ "SKA". Skatelescope.org. 2012-05-25. Retrieved 2012-06-29. 
  22. ^ RiAus 2011, Radio Astronomy: Something Kinda Awesome, (SKA), viewed 1st October 2014, http://vimeo.com/23460933/
  23. ^ "Construction starts on SKA Organisation headquarters". SKA Organisation. 18 April 2012. Retrieved 26 May 2012. 
  24. ^ Koenig, Robert (18 August 2006). "RADIO ASTRONOMY: Candidate Sites for World's Largest Telescope Face First Big Hurdle". Science (AAAS) 313 (5789): 910–912. doi:10.1126/science.313.5789.910. PMID 16917038. 
  25. ^ Amos, J. Nations vie for giant telescope, BBC News, 28 September 2006.
  26. ^ Science Network WA, 16 February 2007[dead link]
  27. ^ "Aiming for the skies". The Age. Australia. 7 April 2008. Retrieved 22 May 2014. 
  28. ^ a b Flitton, Daniel (10 March 2012). "Australia on the outer for largest space telescope". The Age. Retrieved 9 March 2012. 
  29. ^ "Further delays signalled in super-telescope plan". The Australian. AFP. 5 April 2012. Retrieved 10 April 2012. 
  30. ^ "Australia - SKA Telescope". SKA. 2014. Retrieved 22 May 2014. 
  31. ^ Osborne, Darren. "Outback observatory open for business - ABC News (Australian Broadcasting Corporation)". Abc.net.au. Retrieved 2012-10-07. 
  32. ^ South African SKA website
  33. ^ Murchison Widefield Array website
  34. ^ Tom Osterloo, Marc Verheijen, & Wim van Cappellen (June 10–14, 2010). "The latest on Apertif". ISKAF2010 Science Meeting. arXiv:1007.5141. 
  35. ^ Aerospace-Technology
  36. ^ EMBRACE website
  37. ^ e-MERLIN website
  38. ^ EVLA website
  39. ^ LWA website
  40. ^ SKAMP website
  41. ^ NENUFAR website
  42. ^ SKA selects NenuFAR as a Pathfinder
  43. ^ ATA website
  44. ^ LOFAR website
  45. ^ Ray P. Norris (January 7, 2011). "Data Challenges for Next-generation Radio Telescopes". arXiv:1101.1355. doi:10.1109/eScienceW.2010.13. 
  46. ^ AAVP website
  47. ^ Canadian SKA Program website
  48. ^ PREPSKA website
  49. ^ SKATDP website
  50. ^ Nordling, Linda (22 March 2011). "Mining plans pose threat to South African astronomy site". Nature. Retrieved 27 June 2011. 
  51. ^ "Mozambique: Exact Location of SKA Telescope Sought". AllAfrica. 26 June 2012. 
  52. ^ Report and Recommendation of the SKA Site Advisory Committee (SSAC)
  53. ^ "Planning for the radio astronomy service". Retrieved 3 June 2012. 
  54. ^ Carpenter, Avery (22 February 2012). "Oz telescope body under microscope after ex-chairman raises difficult questions". The Star. 
  55. ^ Butoi, Mario (7 November 2014). "October 2014 - Strike delays SKA Dish Installations". Mail & Guardian. 

External links[edit]

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