From: alain245@videotron.ca   
      
   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   
      
      
   Alain Fournier   
      
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