Facilities

The Square Kilometre Array (SKA)

SKA

The SKA is a multi-purpose radio telescope, covering the frequency range from 70 MHz to >25 GHz, that will play a major role in answering key questions in modern astrophysics and cosmology. It will be one of a small number of cornerstone observatories across the electromagnetic spectrum that will provide astrophysicists and cosmologists with a transformational view of the Universe.

Timeline

The SKA will have collecting area approaching one million square metres and be capable of observing across a wide frequency range. Its construction is thus a major undertaking and will be implemented in phases to allow significant observations to be made before construction is completed. The international project has adopted the following terminology to describe this phased approach: Phase 1 is the initial deployment (15-20%) of the array at mid-band frequencies, Phase 2 gives the full collecting area at low and mid-band frequencies (~70 MHz to 10 GHz), and Phase 3 sees the implementation at higher frequencies of 25 GHz or more.

2024 Full Operation

2023 Completion

2019 First Science

2016 Initial Construction

2013-15 Detailed Design and Production Engineering

2012 Site Decision

2008-12 System Design and Costing

2006 Shortlisting of Suitable Sites

1991 SKA Concept

PrepSKA - the Preparatory Phase for the SKA

PrepSKA is a global endeavour involving funding agencies and scientists working together to explore the appropriate legal, policy and technical framework required for the SKA. It is a 3 year €22 M project (€5.5 M from European Community Framework Programme 7 funds), which commenced on 1 April 2008. It is expected that further funding for one year will be provided by the EC, extending the end date to 31 March 2012.

PrepSKA is the umbrella for central and regional engineering work and has the objective of completing the SKA design process to meet the target date of 2016 for starting construction of Phase 1 of the SKA. Information on the national and regional programs is available.

PrepSKA addresses five critical questions that need to be answered to reach a multi-lateral, global agreement on the joint implementation of the SKA, these are:

  1. What is the design for the SKA that can be built on the required timescales and within the target cost?
  2. Where will the SKA be located?
  3. What is the legal framework and governance structure under which the globally-funded SKA project will operate?
  4. What is the most cost-effective mechanism for the procurement of the various components of the SKA? This must take into account the global nature of the SKA and the essential involvement of industry.
  5. How will the SKA be funded? This question is especially important as different countries around the world have different natural cycles to their major funding decisions and may wish to join the project at different times.

The major objective of PrepSKA will be to integrate the R&D work from around the globe in order to develop the fully-costed design for Phase 1 of the SKA and a deployment plan for the full instrument. PrepSKA will produce an implementation plan that will form the basis of a funding proposal to governments to start the construction of the SKA.

PrepSKA involves the following mixture of technical work-packages, aimed at pulling together the international design efforts, and policy work-packages, aimed at developing the governance and legal framework required for construction:

Submission of the formal proposals to construct Phase 1 of the SKA is expected in 2012.

Key Science

The international community has developed a detailed and compelling science case for the SKA, as described in detail in New Astronomy Reviews, volume 48 (2004). The core of the science case is five Key Science Projects; each project represents an unanswered question in fundamental physics or astrophysics, is science either unique to the SKA or for which the SKA plays a key role, and is something which can excite the broader community. The five Key Science Projects are:

  1. Probing the Dark Ages: investigating the formation of the first structures, as the Universe made the transition from largely neutral to its largely ionized state today.
  2. Galaxy Evolution, Cosmology and Dark Energy: probing the structure of the Universe and its fundamental constituent, galaxies, by carrying out all-sky surveys of continuum emission and of HI to a redshift z ~ 2. HI surveys can probe both cosmology (including dark energy) and the properties of galaxy assembly and evolution.
  3. The Origin and Evolution of Cosmic Magnetism: magnetic fields are an essential part of many astrophysical phenomena, but fundamental questions remain about their evolution, structure, and origin. The goal of this project is to trace magnetic field evolution and structure across cosmic time.
  4. Strong Field Tests of Gravity Using Pulsars and Black Holes: identifying a set of pulsars on which to conduct high precision timing measurements. The gravitational physics that can be extracted from these data can be used to probe the nature of space and time.
  5. The Cradle of Life: probing the full range of astrobiology, from the formation of prebiotic molecules in the interstellar medium to the emergence of technological civilisations on habitable planets.

The SKA has been conceived as a observational facility that will test fundamental physical laws and transform our current picture of the Universe. However, the scientific challenges outlined above are today's problems; will they still be the outstanding problems that will confront astronomers in the period 2020-2050 and beyond, when the SKA will be in its most productive years? Thus, the SKA community has adopted "Exploration of the Unknown" as a goal for the facility as part of a firmly founded expectation that the most exciting things to be discovered by the SKA are those that we have not yet conceived.

The science capability of the SKA will evolve as the telescope is constructed. Phase I will enable revolutionary science at decimetre wavelengths, with a particular focus on pulsars and gravitational wave astronomy, magnetism, H I and the nearby Universe, and exploration of the dynamic radio sky.

With its wider wavelength range and 5 times greater sensitivity, Phase 2 will transform our understanding of many key areas including: the formation of the first structures as the universe made its transition from a largely neutral state to its largely ionised state today; cosmology including dark energy via baryonic oscillations seen in neutral hydrogen; the properties of galaxy assembly and evolution; the origin, evolution and structure of magnetic fields across cosmic time; strong field tests of gravity using pulsars and black holes including measurements of black hole spin and theories of gravity, and the exploration of the dynamic radio sky with far greater sensitivity and instantaneous sky coverage.

The high frequency capability of Phase 3 will enable detailed study of planet formation in proto-planetary disks and the detection of the first metals in the universe via observations of molecules such as CO, HCN and HCO+.

Technologies

Three receptor technologies are under consideration for the SKA:

  1. SKA Dishes
    Dishes + wide-band single pixel feeds. This implementation of the mid-band SKA represents a low risk approach to cover the 500 MHz to 10 GHz frequency range. The eventual upper frequency limit will depend on the outcomes of cost-effectiveness studies now being undertaken by a number of regional SKA projects. This design approach is capable of supporting both the Phase 1 science case and most of the Phase 2 key science projects. It is currently the most appropriate technology for implementing the key science topics that require high fidelity imaging observations.
  2. SKA Dishes with phased arrays
    Dishes + Phased Array Feeds. Many of the main SKA science projects involve surveys of the sky made at frequencies below ~3 GHz. To implement these surveys within a reasonable time frame requires a high survey speed. By the use of a Phased Array Feed, a single telescope is able to view a considerably greater area of sky than would be the case with a single feed system. This greatly reduces the time to undertake a survey and can provide a cost effective way of reaching the SKA design goals.
  3. Aperture arrays
    Aperture arrays. An aperture array is a large number of small, fixed antenna elements coupled to appropriate reciever systems which can be arranged in a regular or random pattern on the ground. A beam is formed and steered by combining all the received signals after appropriate time delays have been introduced to align the phases of the signals coming form a particular direction. By simultaneously using different sets of delays, this can be repeated many times to create many independent beams, yielding very large total Field of Views. The number of useful beams produced, or total Field of View, is essentially limited by signal processing, data communications and computing capacity. Aperture arrays can readily operate at low frequencies and can provide large effective areas. Arrays using substantial digital processing systems are inherently very flexible since the system can 'trade' Field of View and bandwidth and hence provide an instrument that can be matched to that required by the experiment.

No detailed array configurations have been developed yet, although it is likely that there will be central high density array surrounded by outer elements. Working Groups are carrying out an analysis of the Phase 2 configuration, to be completed in 2008-09. The Phase 1 configuration will be a subset of that for Phase 2 but is likely to include 75% of the collecting area within 5 km with the remaining 25% deployed out to several tens of kilometres and possibly one element at 100 km primarily for engineering test purposes.

Cost

A number of possible implementations are under consideration, which are estimated to cost €300 M (2007 Net Present Value) for Phase 1 of the array and €1,200 M (2007 Net Present Value) for Phase 2, i.e. €1,500 M (2007 Net Present Value) for the array at frequencies from ~70 MHz to 10 GHz. The Phase 1 and Phase 2 costs include €100 M and €500 M respectively for infrastructure, software, labour, management costs, and delivery; the remaining two-thirds in both cases is for hardware components. Phase 3 of the SKA program, the extension to at least 25 GHz, is less well-defined at this stage, and the technical outlines and costs of its implementation are left to future studies.

Office for the SKA Organisation

The Office for the SKA Organisation is responsible for coordinating the global activities of the SKA project. This includes engineering, science, site evaluation, operations and public outreach. It is located at the Jodrell Bank Observatory. The history runs from he first discussions in 1993, to the establishement of the project Office at the Jodrell Bank Centre for Astrophysics in 2008, and the SKA organisation in 2011. There are currently nine partner countries.