Newsgroups: sci.space.policy
From: Henry Spencer <henry@zoo.toronto.edu>
Subject: telescope cooling (was Re: lunar resources)
Date: Wed, 21 Feb 1996 16:43:04 GMT

In article <4gbfqg$ogk@lace.colorado.edu> fcrary@rintintin.Colorado.EDU (Frank Crary) writes:
>>: ...For cutting edge work, you need
>>: to keep the detectors at cryogenic temperatures...
>>Cutting edge work refers here to IR.
>
>I'm not so sure of that. Low temperatures are certainly more
>important at long wavelengths, but most of the visible 
>wavelength telescopes I'm aware of also use cryogenic
>temperatures for the detectors...

While you *can* run CCDs (the choice for almost all modern visible-light
astronomy) at room temperature, they perform considerably better at LN2
temperatures, so the professionals routinely cool them that way.

>>...The Hubble Space 
>>Telescope manages  to do 'cutting edge work' without...
>
>I'm not sure of that. In space, there are a few tricks to
>get low temperatures without active cooling. I'm not
>familiar with the details of Hubble's design...

The CCDs in the original WFPC ran at -95C using radiative cooling.  I
believe the situation is similar in WFPC2.  I'm not sure about the other
instruments. 
-- 
Space will not be opened by always                 |       Henry Spencer
leaving it to another generation.   --Bill Gaubatz |   henry@zoo.toronto.edu