View Full Version : Discussion: Giant South African Telescope Online

2005-Sep-02, 04:37 PM
SUMMARY: After 5 years of construction, the Southern African Large Telescope is now online, and has captured its first image - the beautiful Lagoon Nebula. The observatory has a massive 10 x 11 metre hexagonal segmented mirror, and state of the art scientific instrumentation. This new observatory provides a good view into the southern skies, which are less covered than the northern hemisphere. More scientific instruments are still being installed, and should be completed within the next few months.

View full article (http://www.universetoday.com/am/publish/giant_optical_salt_comes_online.html)

What do you think about this story? Post your comments below.

2005-Sep-02, 05:24 PM
The press release didn't mention whether this instrument had adaptive optics. Hopefully it does.

Ola D.
2005-Sep-04, 01:39 PM
The press release didn't mention whether this instrument had adaptive optics. Hopefully it does.

As a Community Support member I've contacted David Buckley, SALT Project Scientist, regarding this question, and he answered back..

The answer is that SALT does not - yet - have either a phased primary mirror
array or AO (adaptive optics). Both are things that we're planning to
develop in the future.

In addition the information included below might be of interest to your

In a nutshell: this is FIRST light of SALT, not final ! These are images
taken with the telescope for the first time with its full complement of 91
mirrors and a scientific imaging camera. The active optics system is NOT YET
commissioned, so all of these images are taken open-loop, without the
mirrors being actively controlled at all.

To align the mirrors we use a Shack-Hartmann wavefront sensor at the centre
of curvature. We do this at the start of a night, and repeat the process as
conditions (mostly temperature) change. Although the mirrors are made of a
low CTE material (Astro-Sitall, very like Zerodur), they are supported on
steel mounts which are fixed to a steel space-frame. Thus changes in temp.
can effect the mirror alignment, and lead to image qulaity degradation. Once
we have our edge sensor system installed in a few months, then these
misalignments will be corrected in real-time (every ~20 sec). We have
already demonstrated this on a 37 segment subarray of the mirrors. In
addition to the mirror alignment issue, there is also a misalignment of the
prime focus payload, which also can lead to image quality degradation, and
is present in the first light images.
Finally, the telescope is also tracking open-loop at present so there is a
component of image quality degradation due to the telescope not tracking
properly. Again, this will be addressed shortly when the
autoguidance/focussing system is installed.

This telescope has been built on a relative shoe-string - for a 10-m class
telescope - for a shade over $19M. It does not - yet - have AO. Indeed the
primary mirror segments are not phased even, although this and AO are
planned upgrade paths for the future. The fact that we have achieved "first
light" in just a little over 5 years, I think, was something worth
advertising. Sure, its not perfect yet, but we are well on the way there.


2005-Sep-04, 02:51 PM
I've contacted David Buckley, SALT Project Scientist, regarding this question

Thanks Ola, that's more or less what I was expecting, but now it is certain.