3 ms·

The vaccume of space us too hot for the jwt. It actualky has a cooling system to get it colder than space is. I guess it takes time to get that cold.

stavros 5y ago
Oh huh, really? That's very interesting, thanks.
adhesive_wombat 5y ago
The temperature of deep space is 2.7K due to the cosmic microwave background. JWST's cold side is going to be about 40K, so it's substantially warmer than that. I'm not sure how much of that heat is coming through the sunshield and how much is heat from the equipment.
- citizenpaul 5y ago
  I'm not a physicist I just watched the NASA video explaining that the instruments will need an active cooling system called the cryocooler that cools the stuff below what it can achieve in the vacuum of space on its own.
  - adhesive_wombat 5y ago
    I think that's a pretty poor way for NASA to have put it, because the vacuum of space 1AU from the Sun isn't particularly cold as such. Actually, as a vacuum, it tends to make things there hotter up to a point, not cooler, because you can only radiate that solar heat away. So satellites that are in sunlight, like you are at L2, can easily be at 150°C and even up to 300 depending on various factors. If the JWST were out by, say, Pluto, then you certainly could describe that vacuum as "cold" (inasmuch as a vacuum has a temperature), because you hardly get any sunlight. In fact, Pluto itself has a temperature around 40K.
    - sbierwagen 5y ago
      Design temp for the MIRI detectors is 6.7K. The front end electronics produce some heat, and are in a metal box sealed against light leaks, so they'll need some active cooling. Skimming this paper https://www.stsci.edu/files/live/sites/www/files/home/jwst/documentation/technical-documents/_documents/paper2.pdf https://www.stsci.edu/files/live/sites/www/files/home/jwst/d... it looks like they expect 10.46mW optical module heat, and they've given themselves 36mW of headroom "for conductive and radiative loads." (Heat conducted from the structure, and radiant heat from the the comparatively warm primary mirror?)

stavros 5y ago

Oh huh, really? That's very interesting, thanks.

adhesive_wombat 5y ago

The temperature of deep space is 2.7K due to the cosmic microwave background. JWST's cold side is going to be about 40K, so it's substantially warmer than that. I'm not sure how much of that heat is coming through the sunshield and how much is heat from the equipment.

citizenpaul 5y ago
I'm not a physicist I just watched the NASA video explaining that the instruments will need an active cooling system called the cryocooler that cools the stuff below what it can achieve in the vacuum of space on its own.
- adhesive_wombat 5y ago
  I think that's a pretty poor way for NASA to have put it, because the vacuum of space 1AU from the Sun isn't particularly cold as such. Actually, as a vacuum, it tends to make things there hotter up to a point, not cooler, because you can only radiate that solar heat away. So satellites that are in sunlight, like you are at L2, can easily be at 150°C and even up to 300 depending on various factors. If the JWST were out by, say, Pluto, then you certainly could describe that vacuum as "cold" (inasmuch as a vacuum has a temperature), because you hardly get any sunlight. In fact, Pluto itself has a temperature around 40K.
  - sbierwagen 5y ago
    Design temp for the MIRI detectors is 6.7K. The front end electronics produce some heat, and are in a metal box sealed against light leaks, so they'll need some active cooling. Skimming this paper https://www.stsci.edu/files/live/sites/www/files/home/jwst/documentation/technical-documents/_documents/paper2.pdf https://www.stsci.edu/files/live/sites/www/files/home/jwst/d... it looks like they expect 10.46mW optical module heat, and they've given themselves 36mW of headroom "for conductive and radiative loads." (Heat conducted from the structure, and radiant heat from the the comparatively warm primary mirror?)