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The need to be in the sun isn't about power. Wherever JWST is, it has to be exposed to either the sun or to a planetary body that's shielding it. At the low te
by azernik 5y ago
The need to be in the sun isn't about power. Wherever JWST is, it has to be exposed to either the sun or to a planetary body that's shielding it.
At the low temperatures involved, Earth's night side puts out enough infrared radiation from its own heat to cause problems. JWST is all the way out at Sun-Earth L2 not for power reasons, but so that it will never be in a position where it needs to keep off heat from two different directions.
Nuclear does not help with this. In fact, by having a nearby penetrating radiation source and a high-temperature core mechanically connected to the spacecraft, it may be worse from a thermal perspective.
JWST is a strange spacecraft with very strange design constraints. Your intuitions about planetary/Earth-science or higher-frequency astronomy will not serve you well here.
- asmithmd1 5y agoI am not sure how you know what my intuitions are. My insights come from reading the "design trades" papers about Webb published over the last 20 years. Here is a good place to start: https://www.spiedigitallibrary.org/journals/Journal-of-Astronomical-Telescopes-Instruments-and-Systems/volume-6/issue-01/010902/Review-on-thermal-and-mechanical-challenges-in-the-development-of/10.1117/1.JATIS.6.1.010902.full?SSO=1 https://www.spiedigitallibrary.org/journals/Journal-of-Astro... Yes, insulating an RTG from the IR sensors would have been a challenge, but one that could be completely and accurately tested on earth. The lack of sufficient power directly drove the passive cooling requirement. Which in turn drove the fraught 5 layer shield requirement - which has never been and can't be "Test as you fly" tested on earth. The lack of power also drove the decision to use the experimental 26 Ghz Ka band downlink radio instead of a higher power and more robust X band radio.