re:[Fwd: ATM dark ideas]

["Howard Banich" <Howard.Banich@nike.com>]

This reminds me of the most recent Astronomy magazine article about Mr. 
Angel and the Mirror Lab using borosilicate glass for their mirrors and 
actively cooling them with outside, ambient air. 

I don't recall reading about how they measure the mirror's temperature, or 
even if they do. Perhaps continually flowing outside ambient air through 
the glass is enough, no sensors needed? 

The photo of their prototype 50cm active optics mirror still has me 
drooling. Does anyone know how the system works? How the mirror's shape is 
actively read and corrected?

Probably deceptively complicated or expensive, but it sure looks 
straightforward...

Howard
Portland, Oregon

----------------------[Reply - Original Message]----------------------

Sent by:"Mel Bartels" <mbartels@efn.org>
 


Puddlduk@aol.com wrote:

> Great topic!
>
> Any Ideas on how to measure heat loss of the mirrors?  Ideally one would 
have
> a heating element, an ambient temperature measuring device, and a mirror
> temperature measuring device.
>
> A comparitor circuit would keep the mirror at thermal equalibrium with 
the
> air.  And the difference between watts radiaing into space and 
convecting into
> the mirror from the air could be measured.  The hard part is measuring 
the
> temperature of the mirror while heating it at the same time- Maby an IR
> detector looking in the side of the mirror and the heating element on 
the
> back?
>
> Anyway some measurements could minimise the power used and lead to a 
good rule
> of thumb calculation.
>
> As a side note; I remeber a test question on one of my engineering 
exams.  The
> result was that (with some assumptions) you could freeze water at 40+F 
ambient
> air temperature if the sky was clear and no wind at night.  (This has 
been
> done in India for centuries.)
>
> -Adam Parker



--
Clear skies, Mel Bartels
http://www.efn.org/~mbartels



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