It is an understatement to say that designing and building a world-class scientific instrument comes with its challenges. The Aperture Array Verification System (AAVS1) is one of the major milestones in the journey towards delivering the final design for SKA1-low, the Australian arm of the first phase of the SKA telescope, that will eventually consist of 130,000 antennas observing low frequency signals emanating from the cosmos. The team delivering this project recently reported on the successful roll-out of a station made up of 256 antenna prototypes at the Murchison Radio-astronomy Observatory (MRO), located in Western Australia.
Published by the editorial team, 18 December 2017
“The journey leading up to the deployment and installation of a full antenna station has been a fantastic experience and a steep learning curve for everyone involved”, said the Netherlands Institute for Radio Astronomy (ASTRON) engineer Pieter Benthem, AAVS1 Project Manager. “It’s one thing to design, simulate and test the antennas and systems for AAVS1 inside a computer and a totally different thing to deal with the practicalities and logistical complexities of deploying the array on a remote site, on the other side of the planet.”
Overcoming several technical and logistics issues, the AAVS1 team completed the main station of AAVS1 during their most recent site trip in early November. Previous site trips in August and March showed the dedication of the team.
“Despite being separated from home and family, the team powered on and got a tremendous amount of work done”, added Jader Monari, engineer from the Italian National Institute for Astrophysics (INAF) and AAVS1 Italian group leader. “This fruitful international collaboration showcases much more than just getting ready for the Critical Design Review (CDR) in a few months time. Working at the MRO was quite an experience for many of us coming from the other side of the globe, and the harsh conditions we had to cope with made us bond quite rapidly, with a very positive impact on the team’s performance. Every day, back at Wooleen or Boolardy Station [where the team lodged], we were holding what we called “family meetings”, where we would share joys or frustrations of the day, and discuss the next day’s activities in a professional yet very friendly atmosphere.”
Engineers from ASTRON (the Netherlands), ICRAR (Australia), INAF (Italy), Oxford University (UK), and University of Malta in front of antennas part of the Aperture Array Verification System Test Platform. Credit: ICRAR
The AAVS1 project is a key deliverable for the Low Frequency Aperture Array (LFAA) consortium, bringing together a team of experts from Australia, the United Kingdom, Malta, the Netherlands and Italy. LFAA, led by ASTRON, is one of 12 consortia in charge of designing the various elements for the SKA telescope.
”Getting the actual designers to the MRO has been a great opportunity to allow them to assemble, test and deploy their design”, added Pieter Benthem. “Several lessons were learned across the board from deployment to commissioning, including details on local materials to be used and feedback towards the next design iteration; all valuable input that will inform the design process ahead of the CDR and help prepare for SKA1-low.”
“This is really one of those projects where the whole is far greater than the sum of its parts”, commented Philip Gibbs, LFAA Project Manager at the SKA Organisation. “Every single individual has brought a great deal of expertise to the deployment of the full station. To name but a few examples of this truly international team, the design of the AAVS1 antenna prototypes was led by the University of Cambridge in the UK; procurement of fibre optics and circuit board design was done by INAF in Italy; both INAF and ASTRON purchased and produced the digitisers boards, gathering important know-how on different production techniques on a single printed circuit board design; our Maltese colleagues along with a team at Oxford University applied their expertise in the firmware, monitor and control software of the antennas; and of course our Australian colleagues from ICRAR and Curtin University provided all logistical support to bring this prototype to life in the West Australian desert drawing on their extensive expertise for constructing and deploying radio telescopes in remote regions. ICRAR and Curtin engineers also designed the intra-station power and fibre distribution system, without which the AAVS1 antennas would have no power and the signals received would not be able to leave the station. All of this being overseen and managed by ASTRON in the Netherlands—so indeed, a truly global enterprise.”
The AAVS1 test platform is located at the Murchison Radio-astronomy Observatory (MRO), 800 km north-east of Perth, Western Australia, is home not only to the future SKA1-low telescope but also to the precursor facilities, the Australian SKA Pathfinder (ASKAP) telescope—a 36-dish instrument— and the Murchison Widefield Array (MWA) —comprising 2,048 dipole antennas. The MRO is owned and operated by CSIRO, Australia’s national science agency, which also designed and operates ASKAP. CSIRO’s engineers, responsible for ASKAP operations, have also supported the LFAA team through deployment according to ICRAR’s David Emrich. “CSIRO people are always willing to lend support, tools and in-kind assistance and the engineers, along with the site support staff, have established a really collaborative culture. It makes a difference in this harsh and extremely remote location,” he said.
Left: An aerial view of the core part of CSIRO’s Australian SKA Pathfinder (ASKAP). Credit: CSIRO Right: An aerial view showing some of of the 256 “tiles” belonging to the Murchison Widefield Array. Credit: ICRAR
Both of these telescopes have been instrumental in testing and further developing the technologies for the SKA however, the low-frequency MWA telescope provided test and development precedents for AAVS1. Online since mid-2013, MWA receives signals from the early Universe within the bandwidth of 80 to 300 MHz. Through its years of operations and refining of techniques, the MWA has pioneered methods for AAVS1, such as adjusting for the distorting effects of the ionosphere above the Murchison, and also refining the method to reduce the noise inherent in the system. ICRAR also planned the deployment of the LFAA which at the start of pre-construction in 2013 was considered the critical risk to realising SKA1-low. AAVS1 has been informed by the development of the LFAA deployment plan.
The AAVS1 station. Credit: ICRAR
However, deploying the AAVS1 prototype has been one of several challenges faced by the LFAA consortium team. Drawing from a decade of engineering work worldwide in low-frequency radio astronomy, the team has learnt from MWA, LOFAR and others operating in the same radio frequency regime and has developed improved antenna designs for SKA1-low. These designs, known as the SKALA prototype design, are a log periodic design with various different rung lengths which enable sensitivity to a wide range of frequencies —which operate from 50 to 650 MHz. The continuous evolution of the SKALA prototype has led to the proposed SKALA4 design, an evolution of SKALA2 which has been deployed on site as part of the AAVS1 project.
An international panel of experts tasked with evaluating multiple performance and design metrics of various proposed antenna designs, considers the SKALA4 antenna to be the best option for the LFAA Critical Design Review (CDR) in July 2018. A comprehensive report on this design will be presented for the Review in July.
An AAVS1 antenna in the field at the Murchison Radio-astronomy Observatory alongside a schematic showing the design for Low Frequency Aperture Array antennas.
“With the march towards CDR in 2018, I couldn’t be more impressed and proud with the momentum within the LFAA consortium”, said LFAA consortium leader Jan Geralt Bij de Vaate from ASTRON. “As we move forward on both the deployment, debugging and upcoming commissioning of the AAVS1 station, work throughout the rest of the LFAA consortium has been progressing at full speed. So the next few months will see work progressing towards CDR.”
The AAVS1 journey itself has been documented and you can watch the teaser video below, courtesy of ICRAR-Curtin University.