Infrared Emissivity Table

Aluminum's emissivity varies significantly depending on the surface treatment, and exactly how you are measuring it. Anyway, as you can see there's lots of materials with emissivities close to 1. This is not a hard problem. Commercial satellites do in fact use off the shelf chips all the time. Heck, I used to work at a company founded by satellite engineers. Their previous big project was a space telescope that was entirely built with automotive rated electronics. It lasted for years in orbit with no serious problems. You achieve this with redundancy and error tolerant software. Which is easier these days because automotive electronics standards have also created a big market for error tolerant devices, eg cheap microcontrollers with ECC RAM and SEU tolerance. $100k silicon on sapphire chips just aren't as commonly used as you think they are. It's actually to the point now where for a lot of satellites the engineers actually _prefer_ using automotive rated parts as in many circumstances they're more reliable than the pricey space rated stuff.

...and LEO is a more forgiving radiation environment than deep space. Okay, I'll grant you your automotive-grade ASICs. We haven't solved the thermal engineering, not at all. There are many materials with high emissivity, but you also want high thermal conductivity, high electrical conductivity, high toughness and high strength. Unobtanium. There are good reasons why aluminium is standard, and whatever the treatment its emissivity sucks at any temperature that automotive-grade electronics can be expected to survive. Shall we re-run your calculations, as a second-approximation with a plausible emissivity (0.2) and a delta-T budget for heat-spreaders/heat pipes (10C ?).