Are there many of those current satellites running gpus and actually generating lots of heat?

Principally speaking, as much energy as satellite receives from solar panels it needs to send away - and often a lot of it is in the form of heat. So, the question is, how much energy is received in the first place. We currently have some quarter of megawatt of solar panels of ISS, so in principal - in principal - we know how to do this kind of scale per satellite. In practice we perhaps will have more smaller satellites which together aggregate the compute to the necessary lever and power to the corresponding level.