For a benchmark - the IIS uses about 4500sqft (420 sqm) of radiators just to keep it's onboard equipment (~70KW) cooled. That's ~150-200 W/sqm.
That means, per GPU, you'd need about 2.5-3.0 sqm of passive radiators.
For a 1MW satellite (~8 datacenter racks of GB200/NVL72) you'd need basically half a football field of bleeding-edge solar panels (that also need to radiate their heat on the reverse side) and a similar sized cooling array of heat radiators for the electronics.
This is on the scale of 40-50 tons - about 10% of the IIS. This should fit on falcon heavy or starship - assuming the solar array and radiators can fold up to fit inside. You could, purely based on weight, launch 2 of these per starship launch.
If you consider the Opex savings (electricity, rent, facilities maintenance) and putting 2 of these on a single starship launch, I still think the ROI would be too long. You're saving about ~$1M per year in Opex but it's costing you $25M to launch it into space and likely an extra ~$50M in satellite equipment (based on starlink satellite costs) on top of the compute. Will those GPUs still be useful in 10 years? Probably not.
I don't think the math is there that justifies the free electricity - even at gigawatt scale (thousands of satellites mass-produced) and at a dramatically lower cost per satellite and per launch. Getting costs down on this would involve tightly integrating the compute and the satellite hardware which would make upgrading the compute independently from the cooling/power infrastructure in the future a significant challenge.