> long with Webb's three other instruments, MIRI initially cooled off in the shade of Webb's tennis-court-size sunshield, dropping to about 90 kelvin (minus 298

> long with Webb's three other instruments, MIRI initially cooled off in the shade of Webb's tennis-court-size sunshield, dropping to about 90 kelvin (minus 298 F, or minus 183 C). But dropping to less than 7 kelvin required an electrically powered cryocooler. This seems hard to believe - I get that you have a bunch of radiation flying around (including IR from the sunshield itself) that prevents passively cooling off to 0K (or the CBR's 3K) - but 90K? Is the space itself around L2 really effectively that "hot"? Or is it that passive cooling would just get intolerably slow and you might just as well deploy the tech you need to go from whatever the equilibrium is to below 7K earier?