World's largest radio telescope has been completed!

[Yousuf Khan]

Construction of the Five-hundred-meter Aperture Spherical Radio
Telescope (FAST) is complete, but debugging has only just begun.

> FAST has twice the effective collecting area of the Arecibo Observatory in Puerto Rico and will scan twice as much sky (see ‘Galactic giant’). Size matters because many celestial objects are tough to detect. Spinning stars called pulsars and the cosmic clouds of hydrogen that hold clues to the origin of the Universe emit faint signals, whereas mysterious ‘fast radio bursts’ are transient. A larger -telescope increases the number of signals available, aiding the discovery and characterization of such objects.

http://www.nature.com/news/daring-chinese-telescope-is-poised-to-transform-astronomy-1.20681

[Serigo]

Behind the curve

But FAST’s construction was not easy, and its reliability is not a
given. Like Arecibo’s, FAST’s dish curves like a sphere. Such a surface
is the simplest and cheapest to build, and means that the dish receives
signals from a broad swathe of sky. But unlike steeper ‘parabolic’
dishes, it does not concentrate the signals at one point, and so there
is a loss of focus, causing FAST’s designers to opt for a radical solution.

Arecibo has mirrors attached to its dish to correct for the loss of
focus, but a similar set-up for FAST would have meant 10,000 tonnes of
metal hanging over the dish. Instead, FAST’s surface is made up of some
4,500 panels, some of which can be tilted, raised and lowered by 2,225
actuators to temporarily make it parabolic.

But this makes FAST extremely complicated. The 100-metre-wide parabolic
Green Bank Telescope in West Virginia has about 2,000 moving panels to
help it maintain its shape, but these usually shift by only a few
centimetres, says astronomer D. J. Pisano at West Virginia University in
Morgantown, who has studied hydrogen clouds for 10 years using Green
Bank. “For FAST they will be moving the panels over distances of
metres,” he says. “This is definitely a challenge.”

[Yousuf Khan]

On 9/28/2016 10:22 AM, Serigo wrote:
> Behind the curve
>
> But FAST’s construction was not easy, and its reliability is not a
> given. Like Arecibo’s, FAST’s dish curves like a sphere. Such a surface
> is the simplest and cheapest to build, and means that the dish receives
> signals from a broad swathe of sky. But unlike steeper ‘parabolic’
> dishes, it does not concentrate the signals at one point, and so there
> is a loss of focus, causing FAST’s designers to opt for a radical solution.
>
> Arecibo has mirrors attached to its dish to correct for the loss of
> focus, but a similar set-up for FAST would have meant 10,000 tonnes of
> metal hanging over the dish. Instead, FAST’s surface is made up of some
> 4,500 panels, some of which can be tilted, raised and lowered by 2,225
> actuators to temporarily make it parabolic.
>
> But this makes FAST extremely complicated. The 100-metre-wide parabolic
> Green Bank Telescope in West Virginia has about 2,000 moving panels to
> help it maintain its shape, but these usually shift by only a few
> centimetres, says astronomer D. J. Pisano at West Virginia University in
> Morgantown, who has studied hydrogen clouds for 10 years using Green
> Bank. “For FAST they will be moving the panels over distances of
> metres,” he says. “This is definitely a challenge.”

Good information!

Yousuf Khan