Comment by terramex | Hacker News Reader

Comment by terramex | Hacker News Reader

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Final optical instruments were integrated in 2014, proposed launch date at the time was 2018. There was not enough time to think about any upgrades and cost was ballooning anyway.

NIRCam has quantum efficiency of 70 to 90% depending on light frequency. https://jwst-docs.stsci.edu/files/97978241/97978242/1/159607...

MIRI has average efficiency of about 50%. https://jwst-docs.stsci.edu/files/97977640/97977649/1/159607...

Internal noise of electronics is not significant compared to thermal noise at operating temperature of MIRI (7 Kelvin).

Further small improvements might be possible in the future but no 'orders of magnitude' can be expected without going into even colder temperatures, that would require total redesign.

At the end of the day, efficiency can be offset by simply taking longer exposures so it is nice to have but does not have to be super optimised. Achieving diffraction limit is much more important and JWST's camera do that.

https://jwst-docs.stsci.edu/jwst-near-infrared-camera/nircam... https://jwst-docs.stsci.edu/jwst-mid-infrared-instrument/mir...

The raw efficiency numbers aren't that helpful without a reference. To put it another way, what would the key differences in the component performances look like if you used the state of the art components from this year vs whatever's is in there?

Quantum efficiency is a ratio of how many electrons are created from typical photon hitting a detector. For optical instruments max value is 100% and is the ultimate reference - every photon gets converted into electrical signal. This is why order of magnitude improvements are not expected to happen - there are physical limits on how much signal can be generated from certain amount of light. Solar cells for generating electricity may go over 100% because high energy photons can be converted into 2 electrons but this is undesirable for optical imaging and light will pass through narrowband filters before hitting detector to filter out such photons as they would skew results.

Nancy Grace Roman Telescope to be launched in 2027 is expected to have 75-95% QE for near infrared compared to 70-90% for JWST: https://roman.gsfc.nasa.gov/science/WFI_technical.html

Last upgrade to Hubble near-IR instrument in 2009 (WFC3) has about 75% QE: https://www.researchgate.net/profile/Bernard-Rauscher/public...

Is it simplified model, real life detectors have more parameters regarding noise and persistence but all produced in past 20 years are close to theoretical limits.

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