
Five Hundred Meter Aperture Spherical Telescope - upen
http://sciencebulletin.org/archives/5945.html
======
tf2manu994
Bit of an amateur question, but why a bunch of triangles instead of just a
perfectly smooth curve?

~~~
dalke
The triangles are curved.
[https://arxiv.org/ftp/arxiv/papers/1105/1105.3794.pdf](https://arxiv.org/ftp/arxiv/papers/1105/1105.3794.pdf)
says:

> The surface of each panel unit has been adjusted to the spherical surface of
> radius 318.5m other than the overall 300m radius of the main reflector,
> which will make it better fit to a paraboloid.

They are also under dynamic control, through cables connected to the triangles
(see figure 6 from that paper). Quoting [http://earthsky.org/todays-
image/china-five-hundred-meter-ap...](http://earthsky.org/todays-image/china-
five-hundred-meter-aperture-spherical-telescope) :

> Unlike Arecibo, which has a fixed spherical curvature, FAST will use active
> optics. Its surface will adjust in different directions with more
> flexibility than the surface of Arecibo. That means it’ll cover the sky
> within 40° from the zenith, or overhead point, in contrast to Arecibo’s 20°
> range.

Quoting [http://www.caltechmicrowave.org/fast-
telescope](http://www.caltechmicrowave.org/fast-telescope)

> It will use an active surface that adjusts to create parabolas in different
> directions, with an effective dish size of 300 m. This means that it will
> not be confined to pointing directly upwards, but capable of covering the
> sky within 40 degrees from the zenith. Its working frequency will be 0.3 to
> 3.0 GHz, with a pointing precision of 4 arcseconds.

