But speaking of that: how long is too long to spend at 26K in a vacuum? Are there any good articles/videos that talk about what happens to various materials at such extreme temperatures in a vacuum?

When immersed in a vacuum the conduction and convection heat transfer paths are sharply reduced, so the question then becomes how fast do you cool off via radiation alone?

I'm not a physicist so I don't know, but it's certainly nowhere near as fast as conduction/convection (in fact I believe heat dissipation was actually problematic for many spacecraft designs).

Actually, it's the other way around. Under a clear sky at the surface of the earth, radiation is much more efficient than convection and conduction to air. This is why objects at the surface readily cool below air temperature at night.

Source: http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/coobod.htm...

The linked example is a person losing heat energy under normal circumstances (23 C ambient, body temperature of 34 C). The example shows that a body loses 17 watts to perspiration, 11 watts to conduction (to the air and environment), and 133 watts to radiation.

Contrary to what many people think, a planet without an atmosphere loses heat to space very efficiently, solely by radiation -- indeed, that mechanism is more efficient in the absence of an atmosphere. But even with an atmosphere, radiation is the major heat loss mechanism, most more efficient than convection.

http://science.nasa.gov/science-news/science-at-nasa/2001/as...

It's got 100,000 watts of solar power, so that combined with good insulation means it won't freeze as long as the panels keep working...