alt Hacker NewsIt's not as exciting as you think it is. "emissivity higher than 0.99 over a wide range of wavelengths" is basically code for "it's, like, super black"
The limiting factor isn't the emissivity, it's that you're having to rely on radiation as your only cooling mechanism. It's super slow and inefficient and it limits how much heat you can dissipate.
Like the other person said, you can't do any better than blackbody radiation (emissivity=1).
Yes, graphene appears to offer a negligible improvement over other kinds of paints based on black carbon, e.g. Vantablack.
The research article linked above does not claim a better emissivity than Vantablack, but a resistance to higher temperatures, which is useful for high temperature sensors (used with pyrometers), but irrelevant for a satellite that will never be hotter than 100 Celsius degrees, in order to not damage the electronic equipment.