ASKAP, as a precursor to the SKA, is designed to complete high-speed surveys with high dynamic range in order to produce some of the best radio astronomy data in the world. To do this, there is a complicated web of different technologies from a variety of disciplines coming together for a common goal: “Thousands of components have been installed and connected together to form one of the most complicated and powerful radio astronomy signal processors ever developed.” (from Australian Square Kilometre Array Pathfinder: I. system description)
It takes many people from all over the world to achieve this fantastic feat of modern engineering and science. In 2019, ASKAP became technologically operational after 10 years of designing, prototyping, construction and commissioning.
Since 2019, teams have been running survey science projects to test ASKAP’s capabilities and fine-tune its technologies ready for full survey science in 2022. Read more about this on our science page.
To explore the technologies in more detail, the paper Australian Square Kilometre Array Pathfinder: I. system description, was published in Publications of the Astronomical Society of Australia, 2021. Selected contents of the paper are presented below.
| Feature | Value |
|---|---|
| Antennas | 36 |
| Antenna diameter | 12 m |
| Focal ratio f/D | 0.5 |
| Total collecting area | 4,071.5 m2 |
| Maximum baseline | 6 km |
| Angular resolution | 10″ at 1 GHz |
| Observing frequency | 0.7-1.8 GHz |
| Processed bandwidth | 288 MHz |
| Frequency channels | 15,552 |
| Frequency resolution | 18.5-0.58 kHz |
| Effective system temperature | 75 K |
| Sensitivity | 54 m-1K-1 |
| Dual polarisation beams | 36 |
| Field of view (800 MHz) | 31 deg2 |
| Field of view (1,700 MHz) | 15 deg2 |
| Survey speed (800 MHz) | 91,400 m4 deg2 K-2 |
| Survey speed (1,700 MHz) | 44,200 m4 deg2 K-2 |
The Antennas
Compared to existing telescopes, it was clear that high survey speed could be achieved by building an array of many small antennas to keep the primary beam size large, provide sensitivity over multiple spatial scales, and achieve good surface brightness sensitivity. Such an array would have many baselines (antenna pairs) and would, therefore, produce a very large amount of data and cause the computational cost of imaging to dominate array design.
ASKAP has 36 antennas that are 12m in diameter. Of the 36 ASKAP antennas, 27 were placed to provide a Gaussian distribution of spatial scales, three additional antennas were added to the core of the array to increase surface brightness sensitivity and another six antennas were added on longer baselines (up to 6 km) in a Reuleaux triangle to provide improved resolution for compact sources.
The antenna structure consists of a steel pedestal and support frame, topped with solid panels made of non-metallic honeycomb sandwiched between aluminium sheets. The feed is located at the prime focus.
The graph below shows the location of each ASKAP antenna plotted relative to Antenna 1. A circle of radius 1 km is drawn for scale.
Phased array feeds
Each phased array feed is made up of 188 individual receivers, positioned in a chequerboard-like arrangement. Alongside the receivers are low-noise amplifiers, which greatly enhance the weak radio wave signals received. These components are housed in a water-tight case mounted at the focal point above each of ASKAP’s antennas. Together with specialised digital systems developed for ASKAP, the phased array feeds create 36 separate (simultaneous) beams to give a field-of-view of 30 square degrees on the sky.
Read more on PAFs technology at the dedicated CSIRO page.
Supercomputing power
With up to 36 beams per antenna and 36 antennas, ASKAP produces a torrent of raw data (approximately 100Tbit s–1). The digital signal processing system begins with digital receivers processing 192 signals which include 188 from each PAF, 2 calibration signals, and 2 spares for future applications such as radio frequency interference mitigation. The raw data is correlated and averaged at the observatory, producing an output visibility data stream of up to 2.4GB s–1 that is sent via optical fibre to the Pawsey Supercomputing Centre in Perth, some 600 km south of the telescope, for image processing. This gives the research community a hint of the challenges to come in the era of the SKA. Read more on how ASKAP and Pawsey work together on the Pawsey project page or the CSIRO’s dedicated Pawsey page.
Final data is stored on CSIRO’s ASKAP Science Data Archive (CASDA),where it is accessible to the astronomy community.
The below diagram shows the flow of data from its collection point at the dish, through the MRO processing facility to the Pawsey Supercomputing Centre.
There’s so much more to it…
More detail on these components, and the many other technological elements needed to generate the best radio astronomy data in the world, treat yourself to the paper Australian Square Kilometre Array Pathfinder: I. system description, that was published in Publications of the Astronomical Society of Australia, 2021.
To submit a proposal to use ASKAP, visit the Observation Management Portal. For more information on using ASKAP, visit the dedicated Confluence page.
ASKAP is an SKA-precursor telescope situated at the MRO in Western Australia.
We acknowledge the Wajarri Yamatji as the traditional owners of the Murchison Radio-astronomy Observatory site.