| General > General Technical Chat |
| JAMES WEBB SPACE TELESCOPE cooling it's jets |
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| GreggD:
Current status: https://jwst.nasa.gov/content/webbLaunch/whereIsWebb.html?units=metric The temperature in French Guiana (launch site) is virtually all year around the value of 30°C 303°K 86°F If Webb was not cooled on the pad then when the fairings exposed Webb to space, the Instrument Radiator would radiate 468W/m² Now almost two months later it has cooled to 43°K -231°C and radiates 172mW/m² Dropping another 6.68° photon radiation will drop by 50% This is why it will take months to cool. At 20°K it will radiate 9mW/m² Instrument Radiator Temp(K) 42 Space Temp (K) 4 Area m² 1 Emissivity 0.98 Stefan Boltzmann constant 5.6702E-08 Watts of Photon radiation 0.17289 Emissivity*Stefan Boltzmann constant*Area m²*((Instrument Radiator Temp (K)E4)-(Space Temp (K)E4)) The mirrors are gold and almost do not radiate, emissivity 0.02, they cool from the back non-gold side. |
| RoGeorge:
--- Quote from: GreggD on February 21, 2022, 08:54:25 pm ---If Webb was not cooled on the pad then when the fairings exposed Webb to space, the Instrument Radiator would radiate 468W/m² Now almost two months later it has cooled to 43°K -231°C and radiates 172mW/m² --- End quote --- Cool, never thought of that aspect, thanks! :-+ On a second thought, maybe they should have heat it on the launch pad instead. https://en.wikipedia.org/wiki/Mpemba_effect ;D |
| Rick Law:
We have waited for 15 years for it to launch (initial planned launch 2007), another few months is not going to make much difference... But I sure am anxious to see what new things we can learn. I am retired now, otherwise known as being "in God's waiting room", tick tock tick tock tick tock... Come'on, cool it, soon... I am anxious and impatiently waiting for the telescope results. |
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