The real question is what is your budget? At the very high end, you could get a custom machined box for the heat sinks and customized components. You could also actually pay someone to calculate the thermodynamics and heat flows. As others have stated, detailed specs (application, requirements, budget, timeline, quantity) are really a requirement.
I'm guessing that there are military, aircraft solutions that fit the bill (but might require you to drop $10K on the system. It seems to me that the requirements for satellites are at least as stringent -- and repair isn't an option.