Sky and Telescope - February 2017 - 28

FAST Radio Telescope

Building FAST
Dawodang wasn't completely uninhabited, and in October
2009 the 65 villagers living there were moved into new apartments in the nearby town of Kedu. Then, to create a radioquiet zone, an additional 9,110 residents living within 5 km
of the telescope site were resettled to two contiguous towns.
China Railway Construction Corporations Limited
coordinated the construction effort, a mammoth task made
more difficult because the primitive roads near the site were
too narrow for large equipment and vehicles. So the first task
was building a 7-km-long access road. Then the Dawodang

S JIGSAW PUZZLE On July 3, 2016, workers installed the last of
4,450 triangular panels that form the telescope's reflective surface.

28

F E B R U A R Y 2 0 1 7 * SK Y & TELESCOPE

RUSSIA

M ONGOL IA
Beijing

CHINA

FAST
INDIA

Hong
Kong

S REMOTE AND QUIET FAST was built in a sparsely inhabited section
of south-central China - a location with little radio interference from
terrestrial sources.

sinkhole had to be reshaped to provide a solid base, and this
meant digging out more than 900,000 cubic meters of dirt
and stone. Also, to protect the antenna from flooding, crews
carved out a 1.1-km-long drainage tunnel.
The real construction started in November 2012. A ring
of 50 support columns appeared first, and then those were
topped by an annulus of steel girders. Next came the installation of 8,895 thick steel cables, suspended over the giant, circular hole to form a sphere-shaped "net"; adding thousands
of tie-down cables anchored into the ground; and, finally,
attaching the telescope's shiny "skin."
FAST's big dish consists of 4,450 triangular panels, each 11
m on a side. It has a total mass of more than 2,000 tons and
a combined reflecting area roughly equal to 30 soccer fields!
The deep, spherical bowl has a 300-m radius of curvature.
A unique - and unprecedented - aspect of the FAST
design is that a portion of its surface can be reshaped in real
time into a paraboloid, which concentrates all the incoming
radio energy from that area at a single focus. As the diagram
at upper right shows, a spherical surface can't do that. At
Arecibo, which has a spherical reflecting surface, the focus is
strung out along a line.
Computers will change FAST's shape using 2,226 mechanical actuators. Anchored to the ground at one end, each actuator is connected by a cable to a node where the corners of six
panels meet. These devices can shorten their respective cables
by about 47 cm (18½ inches) and can be manipulated independently. Working together, they can alter any portion of
the surface to form a real-time paraboloidal reflector with an
effective diameter of 300 m. Di Li, one of FAST's project scientists, refers to this arrangement as "a bowl within a wok."
In order to concentrate a signal reflecting from such a
large area into a table-sized focal plane, all the panels had
to be manufactured very precisely. Also, the shape of the

BOT TO M: CHINESE ACA DEM Y OF SCIENCES / CH AO ZH A NG; M A P: SK Y & TELESCOPE / LE A H TISCIONE

a large, single radio antenna at a comparative low construction cost. In addition, the surrounding peaks and sparse local
population would minimize electromagnetic interference.
With dreams of hosting the SKA dashed, Nan championed
the idea of going forward with an enormous dish anyway.
The site would be a nearly perfect depression about 170 km
southeast of Guiyang, the provincial capital of Guizhou, and
known locally as Dawodang (meaning "grand puddle").
Meanwhile, engineers carried out studies on the critical
technologies that would be needed, including a deformable
reflecting surface, systems for precisely measuring and
controlling its shape, a lightweight housing and cable-driven
transport system for the instrument's receivers (to be suspended over the dish), and the receivers themselves.
Thanks in part to China's booming economy, government
officials finally gave the green light to the FAST project in July
2007, providing 1.2 billion renminbi (about $180 million) for
the giant receiver's construction.



Sky and Telescope - February 2017

Table of Contents for the Digital Edition of Sky and Telescope - February 2017

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Sky and Telescope - February 2017 - Cover1
Sky and Telescope - February 2017 - Cover2
Sky and Telescope - February 2017 - 1
Sky and Telescope - February 2017 - Contents
Sky and Telescope - February 2017 - 3
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