QUESTION:
If space is near absolute zero, why do you need to cool the craft? Is the 2
rpm rotation not sufficient to keep the sun from heating the craft?

ANSWER from Rob Manning:
For the same reason the rotating Earth does not cool it to the ambient deep
space temperature of 3 degrees Kelvin (just above absolute zero), Mars
Pathfinder adopts the "average" thermal energy of the whole "sky", including
the very hot Sun. Although the Sun takes up less than a fraction of a
percent of the "sky" as seen by Mars Pathfinder, it's surface is millions of
degrees hotter than the surrounding deep space. That is enough to "average"
the temperature of the spacecraft to a little colder than room temperature
(to calculate the temperature right, you also need to factor in the
spacecraft's emissivity and absorbtivity). So the spacecraft's average
temperature is around 10 deg Celsius. That would be great except for another
point: we have "hot spots" built into the design. So that we can keep the
lander's electronics and battery cool while on the surface of Mars, we
intentionally surrounded them inside a thermal enclosure (just like the
rover team did with the rover electronics). The problem then is to keep the
lander's electronics (especially the X-band radio transmitter) from roasting
in there while we cruise to Mars. We solved this problem by pumping freon
around the cool perimeter of the cruise stage (those white radiators you can
see on the pictures) and then down inside the lander and rover. The freon
takes the excess heat away from those hot spots and then radiates that heat
into the cold of deep space.

--Rob Manning