If all you want is a low equilibrium temperature, in free space it suffices to have a good-quality sunshade. In the shadow, objects get negligible heating and radiate into the heat sink of interstellar space. (The heat capacity of vacuum is pretty good, per cubic lightyear.)

Of course, the T^4 dependence of black body radiation makes the radiated power damn small at low temperatures.  It's about 460 W/m^2 around room temperature (300 K), but only 2 W/m^2 at the boiling point of nitrogen (77 K).

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