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According to the suggested tags, this must be the right forum:

I found that for each band of Landsat 8 over 7000 detectors are on the array. Does anyone know how big each of the sensors is?

B--rian
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    The official landsat website has many details on the instruments: https://landsat.gsfc.nasa.gov/landsat-8/landsat-8-overview – B--rian Mar 19 '21 at 11:57
  • This is the wrong forum. Landsat is an Earth observation satellite. It doesn't do astronomy. The Space Exploration stack exchange is the right forum (but this old question is too old to worry about closing) – James K Mar 21 '21 at 16:36

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The answer can be deduced from the main landsat 8 page, where you find the following picture of QWIP detector arrays, and QWIP is short for Quantum well infrared photodetector, I added a gray arrow pointing to one of the 3 arrays.

QWIP detector array

I cannot give you the exact dimensions in mm, but it is clear from the SMD chip elements (SMD = surface mounted device) - one of them I highlighted with a gray ellipse, that each sensor is probably coin-sized, if not smaller. Or in numbers: I guess a side length $1.5\pm1 {\rm cm}$ seems reasonable, it depends a bit whether the sensor has the same size as the silver square or whether there is a border around.

References

B--rian
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    The circled object looks more like a diode in a MELF package to my eye. Same ballpark size though (~2×4 mm). – Alex Hajnal Mar 21 '21 at 11:56
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    @AlexHajnal Could well be. If all you have is a hammer, everything looks like a nail :-) – B--rian Mar 21 '21 at 12:07
  • Does anybody have background info on the screws used? In my experimental years, a screw was almost certainly a M5, but is that true here as well? – B--rian Mar 21 '21 at 12:10
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    Screws on such devices are in my experience always chosen for the required load - and physical dimensions whatever is practical and for how small you can get without compromising stability. Could be anything between M2 and M6. – planetmaker Mar 21 '21 at 13:46
  • it links to the paywalled The next Landsat satellite: The Landsat Data Continuity Mission but even the abstract might be helpful: "two thermal bands with a 100 m resolution" If the focal length of the imaging optics is known, the pixel size can then be estimated. update: Here you go! https://core.ac.uk/download/pdf/188079092.pdf – uhoh Mar 21 '21 at 14:48