You use radiation for cooling in space. That obeys the Stefan-Boltzmann law with power scaling with T^4 (so you want the radiators as hot as possible). You can use passive elements, like heat-pipes to move heat to the radiators, but active elements like pumps for forced convection could make sense; and most importantly heat pumps are an active element that can boost the temperature of the radiators vs the thing you're keeping cool (thereby increasing the heat rejection capacity of a given radiator size).