I am currently investigating the thermal behaviour of an ion engine. Since it's being operated in vacuum only radiative cooling is possible. The engine is set up in a vacuum chamber with wall temperatures of about 35 K. I thereby did not model the chamber. I used the surface-to-surface radiation with open system to simulate the heat radiation of the outer surfaces of the engine. I was wondering now if it was legit to set the ambient temperature of each radiation subnode to 35 K or if I have to model the chamber as well. Can someone help me? Thanks in advance!