How environment curbs may impede siting of SKA dishes
SA’s astronomy site in the Northern Cape will eventually host the Square Kilometre Array, but nature reserve plans may impede, writes Sarah Wild
SA’s astronomy site in the Northern Cape will eventually become a nature reserve, according to conservation experts and astronomy officials.
The site will ultimately host the Square Kilometre Array (SKA), which when complete in the 2030s will be the largest radio telescope on Earth.
However, the environmental management plan for the site — expected to be opened for public comment in 2018 — could create no-go zones, hindering the construction of the telescope.
The SKA, shared between SA and Australia, will comprise thousands of dishes and 1-million antennas in those countries. It is intended to answer some of humanity’s most enigmatic questions. Are we alone in the universe? What is dark matter? What happened just after the Big Bang?
Being able to answer these questions hinges on the sensitivity and capabilities of the telescope — which in turn depends on where the dishes and antennas are placed. But the environmental management plan, now with the Department of Environmental Affairs, could restrict where dishes are constructed.
South African law protects wild landscapes, such as those regions of the Karoo that form the astronomy site, from the environmental impact of construction — even if that construction is that of a telescope. The South African Radio Astronomy Observatory (Sarao), which is overseeing activities on the astronomy site has now appointed the South African Environmental Observation Network (Saeon) to implement the environmental plan.
Through its land acquisition programme, the government — through the National Research Foundation, which oversees Sarao — has acquired 138,703ha for the construction and protection of the SKA, says Tracy Cheetham, head of construction planning. "The SKA core area will be declared an environmentally protected area in terms of the National Environmental Management: Protected Areas Act," she says.
The Sarao-Saeon partnership would last three years, with a price tag of R3m allocated for Saeon to deliver on its side of the bargain.
Casper Crous, an ecologist with Saeon, says that they will "classify habitats and biotopes as of ‘high sensitivity’, ‘very high sensitivity’, or ‘no-go zones’.
"A ‘no-go zone’, for example, would be kokerboom [quiver tree] populations, or ephemeral wetlands – areas that if impacted are unlikely to ever recover.
"In these cases, the infrastructure would have to avoid such areas, and construction in those particular areas would thus have to be redesigned," he says.
But dishes of large radio telescopes, such as the SKA, are not placed randomly on a landscape. The SKA will be an interferometer, a telescope in which all the dishes work together as a single instrument to collect weak radio signals from the universe.
"The relative positions of the dishes of an interferometer determine the quality of the resulting telescope beam," says Robert Braun, science director at the international SKA Organisation. The organisation is tasked with overseeing the design and preconstruction of phase one of the SKA.
The relative positions of the dishes of an interferometer determine the quality of the resulting telescope beamRobert Braun
international SKA Organisation
In Australia, SKA1 will have 130,000 antennas — which resemble 2m wire Christmas trees — picking up low-frequency signals. In SA, the SKA will incorporate the country’s 64-dish MeerKAT telescope and add another 130 dishes, bringing the total number of dishes to 194.
These dishes will be laid out in a star formation, with three spiral arms, and they will be densely populated in the core of the telescope, becoming sparser the further away they are from the core.
In November, Sarao erected the 64th and final MeerKAT dish, with the full telescope expected to come online in April 2018.
However, because MeerKAT is also an interferometer, the telescope comes online in phases, as new dishes are added to it.
The constructed and connected parts of MeerKAT have already been doing science and MeerKAT was one of a number of radio telescopes that contributed to the detection of gravitation waves resulting from the collision of two neutron stars. These findings were published in November.
While MeerKAT’s dishes are all on the ground, the additional SKA dishes will be added only from 2019 at the earliest and their placement will depend on the environmental assessment.
"The nominal SKA dish locations have been chosen to provide an optimised sampling of dish separations," says Braun. "The orientation of this pattern, together with the precise degree of spiral winding were chosen to best match the large-scale environmental constraints of the SKA site, particularly avoiding the location of nearby population centres and major transport infrastructure, with their associated potential for radio frequency interference."
Radio frequency interference, from machinery and cellphones among others, is anathema to radio telescopes. However, placing the dishes in environmentally sensitive habitats could damage those environments.
Braun says that his organisation recognises the need for flexibility in terms of where the dishes can go.
Within the core area, dishes can be moved by up to 20m from their ideal placement. Farther away from the core, such as in the spiral arms of
the telescope, dishes can be moved as much as 1.6km. More than those "allowed" shifts could be detrimental to the telescope’s sensitivity.
However, "there may still be instances where this limit may need to be exceeded", Braun says. "In that case, they would require individual study in order to mitigate the beam degradation as far as possible via a more extensive readjustment of the surrounding dish locations in an effort to compensate."
But the Sarao-Saeon agreement also paves the way for Saeon to turn the site into an outdoor natural laboratory.
Crous, who is involved with the Saeon implementation, says it is "progressive of [Sarao] to allow Saeon to study the ecological aspects on their property, which is not only a commitment to responsible construction, but also to better our understanding of land-use change in the Karoo.
"This region is unacceptably understudied compared to other regions in the country. Even less is known about how these biotic and abiotic elements would respond to future changes in land use and environmental conditions including climate change."