How does the space suit control the temperature of an astronaut's body?

The human body has a fantastic ability to control its own temperature. That's why we

don't have to sit out on a sun-lit rock in the morning in order to get ourselves going,

and it's the reason why any ten Inupiat (people whose ancestors have lived in Alaska

for a thousand years) have the same average body temperature that any ten Ibo

(people whose ancestors have lived in equatorial Africa for a thousand years) have,

within a couple tenths of a degree.

We don't need special suits to do it ... unless the space around us stays very hot or

very cold for a long time ... like a child in a closed car in the direct sun on a hot day,

or an under-dressed mountain climber buried in snow for three solid days. Then, our

control machinery wears down, and our body temperature starts to creep in the

direction of the space around us.

If you look closely at the space suits used for running around on the moon or for space-

walking out around the International Space Station, you'll notice they all have this 'box'

on the astronaut's back. That's nothing more than his 'air-conditioner' that keeps the

air inside the suit at a comfortable temperature ... putting some heat in if it gets too

cold in there (which is rare), and taking heat out if it gets too warm in there (which is

much more common). With the air in the suit kept at a comfortable temperature, the

astronaut's body does the rest of the job of controlling its own temperature.