From: alain245@videotron.ca   
      
   On Dec/31/2021 at 21:40, Snidely wrote :   
   > Alain Fournier wrote on 12/31/2021 :   
   >> On Dec/31/2021 at 05:54, Snidely wrote :   
   >>> Thus spake Alain Fournier:   
   >>>   
   >>>> About 10 hours later both the hot and cold sides have heated up.   
   >>>> Why? The sunshield has started to deploy for a few days and   
   >>>> deployment should be completed at launch +5.5 days (in a few hours).   
   >>>> My guess is that it was launched with a limited stock of coolant   
   >>>> that has boiled off and that the sunshield will take care of keeping   
   >>>> it cool now.   
   >>>   
   >>> The coolant is supposed to last for the 10 year mission.  And the   
   >>> limiting resource for the 10 year figure is propellant.   
   >>   
   >> For the most part the telescope is passively cooled. The coolant is   
   >> used only for the Mid-Infrared instrument (MIRI). And I doubt the MIRI   
   >> is cooled yet. Its operating temperature is -266.5C or 6.7K, not in   
   >> the same ball park than the -145C or 131K currently observed on the   
   >> cold side of the JWST.   
   >>   
   >> See: https://webb.nasa.gov/content/about/innovations/cryocooler.html   
   >>   
   >   
   > But where would that "limited stock of coolant" be that boiled off?   
      
   I don't know, it probably never existed. That was just a guess on my   
   part. Niklas Holsti and you have pretty much convinced me that it wasn't   
   a good guess. I'm still not 100% sure there wasn't some short term   
   coolant that boiled off. But I don't think that is very likely.   
      
   Anyway, the temperature seems to have stabilised, at least on the cold side.   
      
      
   Alain Fournier   
      
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