Sky and Telescope - June 2017 - 28

Radio Revolution

NAMIBIA

SOUTH
AFRICA
Cape
Town

8 km

3 km

Perth

Port
Elizabeth

WESTERN AUSTRALIA
mi.
8050km

80 km

Then there's the technical challenge. Building the dishes,
pedestals, and sensitive receivers is one thing, but hooking
every single antenna up to a central supercomputer through
optical ﬁber connections is another. SKA1-mid's total raw
data output amounts to 2 terabytes per second, or over 60
exabytes (60 × 1018 bytes) per year - more than 5% of the
total internet data trafﬁc in 2016. This all has to be processed
in real time by dedicated correlators and data processors to
produce the ﬁnal high-resolution radio images that astronomers are after. The required number-crunching power is on
the order of 350 petaﬂops - 350 thousand trillion calculations (or ﬂoating point operations, hence "ﬂop") per second;
the expected yearly output of archived science data products would ﬁll 7 billion DVDs. As Australian astronomical
computing expert Andreas Wicenec (University of Western
Australia) says, "The deluge continues."

Outback Struggles
I met Wicenec in June 2016 in Perth, Western Australia,
where he's involved in the Australia SKA Pathﬁnder (ASKAP).
Nearing completion at the Murchison Radio-astronomy
Observatory, some 800 kilometers north of Perth, ASKAP is
another SKA precursor telescope. It's a six-kilometer wide,
36-antenna array. The 12-meter dishes are each equipped
with phased array feeds, receivers capable of detecting multiple

radio beams simultaneously, providing the observatory with
an unprecedented 30-square-degree ﬁeld of view - 150 times
the apparent area of the full Moon in the sky.
According to Wicenec, ASKAP produces some 250 terabytes
per day of raw data, more than 15 times the nightly data forecast for the upcoming Large Synoptic Survey Telescope (S&T:
Sept. 2016, p. 14). A dedicated supercomputer called Galaxy
at the Pawsey Supercomputing Centre in Perth processes
the ﬂood. At present, it's the fastest radio observatory in the
world in terms of survey speed. Astronomers expect ASKAP to
eventually map some 70 million radio sources - a thirtyfold
increase over the current number.
Like MeerKAT, the project was largely developed to support
an SKA bid - in the ﬁrst decade of this century, both South
Africa and Australia were hoping to host the future array,
back when the plan was to have it in only one place. But contrary to MeerKAT, ASKAP will not become part of the SKA:
SKA-low will be at the same site, but it will use a completely
different kind of antenna. Instead, says CSIRO's Astronomy
and Space Science director Douglas Bock, ASKAP will be a
great observatory on its own. Bock expects the array to be
completed in 2018.
In May 2012, after a lot of political tugs of war, it was
ﬁnally decided to build the Square Kilometre Array on both
continents. "That wasn't necessarily the cheapest option,"

SKA Precursors
Name

Location

Frequency range

Antenna type

Australia SKA Pathﬁnder (ASKAP)

Australia

700 MHz-1.8 GHz

12-m dish

Hydrogen Epoch of Reionization Array (HERA)

South Africa

50-250 MHz

14-m mesh dish

MeerKAT

South Africa

300 MHz-3 GHz

13.5-m dish

Australia

80-300 MHz

dipole antenna

Murchison Wideﬁeld Array (MWA)
28

J U N E 2 0 1 7 * SK Y & TELESCOPE

LE A H TISCIONE / S&T, SOURCE SK A ORG A NISATION (2)

p ON THE MAP Shown are the preliminary locations for SKA1-mid and SKA1-low. Each South African icon represents a single dish; each Australian
icon represents a station of 256 individual antennas. The insets give a slightly clearer picture, although the sheer scale is still hard to grasp. Designers
chose the spiral configuration because it provides a variety of baseline distances and angles between antennas, enabling very high-resolution imaging
with interferometry. (The best layout would be random, but construction considerations make that undesirable.)

Sky and Telescope - June 2017

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