Ever heard of the Stefan-Boltzmann Law? This dictates the maximum amount of energy that can be radiated from an object per unit area for a specific temperature. The power is proportional to the fourth power of the temperature.
So for example if you have 300W worth of TDP, and a perfect black body radiator of half a square metre, then the radiator temperature is already going to hit your maximum CPU temperature of 50C, assuming it is perfectly shadowed from both the sun and the earth.
Sure, I have studied these things a couple of decades ago. Now that I read my comment above I realize it was badly worded. I didn't mean to say all heat would simply be radiated without posing a problem. I meant that the only way for a body to lose energy in space is by radiation (without ejecting matter, I suppose).
http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/stefan.htm...
So for example if you have 300W worth of TDP, and a perfect black body radiator of half a square metre, then the radiator temperature is already going to hit your maximum CPU temperature of 50C, assuming it is perfectly shadowed from both the sun and the earth.