Indeed. But radiative cooling in vacuum is much slower than conductive cooling per unit surface area (even just in air at sea level on earth, air being a fairly

Indeed. But radiative cooling in vacuum is much slower than conductive cooling per unit surface area (even just in air at sea level on earth, air being a fairly poor conductor) unless you manage to concentrate the heat in your radiator at a massive temperature that most materials can’t withstand. And conductive heat transfer is what’s being measured in the context of this article.