A small question. I know that Webb should be protected from heat during normal operation because its infrared sensors are sensitive to its own infrared emission.

The question is does small degree of heat (before the sunshield is fully deployed for instance) might have an effect on its mirrors' surface? Or other components ? Didn't the launch caused some heating too in this regard?

I know that they will have to be adjusted in the micrometer scale (iirc) when operational. And it seems strange that it can survive intact this long way.


  • $\begingroup$ For the mirrors, the heat is only of concern due to thermal expansion which distorts them mechanically. For the light sensors the sensitive aspect is incoming (including self-emitted) light. A momentary focused direct sunlight will destroy them, that's why the orientation of the JWST is so important. It can never have the Sun in its field of view, once the secondary mirror is deployed, and can also be damaged by direct sunlight on the sensors(but until deployment they are packaged out of light path). $\endgroup$ Jan 2, 2022 at 8:36
  • $\begingroup$ And a small distortion of these carefully crafted mirrors (in micrometer scales) , is not an issue? Or it doesn't reach such temperatures during the voyage? $\endgroup$ Jan 2, 2022 at 10:14
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    $\begingroup$ @user2679290 the mirrors are crafted in nanometers, not in micrometers. $\endgroup$
    – Uwe
    Jan 2, 2022 at 10:18
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    $\begingroup$ @user2679290 No problem, when the distortion is proportionate, unopposed(no bending), and reversible by returning the temperature to the correct regime. The first thing on the mirrors that would permanently be damaged by high temperature are the actuators for finetuning the shaping of the mirrors, and those are supposedly good up to about 400K (but intended to operate only in the 20-80K range, where the beryllium mirrors also exhibit almost null thermal expansion) $\endgroup$ Jan 2, 2022 at 17:13
  • $\begingroup$ Pretty cool. Thanks for the reply. $\endgroup$ Jan 2, 2022 at 17:27

1 Answer 1


enter image description here Well, it is not a full answer, but I want to point out that imperfections in the curvatures can be fixed by using some tiny actuators that change the curvature slightly.

More details here :


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