Re: Overheat?
Philae could overheat because it is in the universe's biggest Thermos bottle (often referred to as "space"). The long legs of the lander means there's somewhere between jack and squat for heat transfer into the icy stuff, and since the icy stuff is low-density, insulating powder and gravel (30% water's density, with vacuum between the particles), you can figure jack left town.
In such an environment the only means of shedding heat available to Philae is radiation, since it eschewed short-term options like the ice sublimation utilized by US space suits. And with internal temperatures of 250 to 320K (guessing), Philae isn't going to be a shining beacon of radiative heat loss. Landing on a section of 67P that is continuously sunlit in this season presents the problem that Philae (covered in dark solar cells) will be warmed by the sun, and warmed by reflected / emitted radiation from the comet, and warmed by its internal components.
A better means of thinking about Philae's situation is not that it is in the cold depths of the solar system attached to a block of ice, but rather than it is a bundle of 32 watts of electronics wrapped in multi-layer insulation and stored in a transparent vacuum bottle. Sunlight at 3AU is shining about 150 watts per square meter onto Philae (which presents about a square meter of area to sunlight), while the reflected light from 67P will be about 7 to 10 watts per square meter. (I don't know how to calculate the infrared burden shed by 67P for all the sunlight it soaks up.) That wattage isn't much, but neither is the rate that Joules are departing the insulated structure in such an environment. It wouldn't take much for the electronics or batteries to exceed their "I smell something funny burning" temperatures.
Taking away Philae's time in shadow (i.e., time when it isn't hit with 150+ watts of extra heat) doesn't help the cooling situation. Apparently, its design is such that engineers are concerned about it overheating.
Biting the hand that feeds IT
