There is the additional problem that the GPUs are not in the panels, so to radiate the heat you must first transport it from the GPUs, then distribute it uniformly over the entire surface of the radiators, otherwise some parts will overheat.

Without gravity, it is likely that this can be done only by pumping continuously a lot of liquid, which will increase the power consumption and it will reduce reliability.

Solar panels that have heat radiators on their backside will have a higher temperature than simple solar panels, where half of the absorbed solar energy is converted into electrical energy and taken away. The efficiency of solar panels decreases with temperature, so hotter solar panels will have to be made bigger for the same electrical energy output.

Maintenance would be too expensive, so a space datacenter would have to be overprovisioned, e.g. with a double number of GPUs, to keep the average of the number of still working GPUs at the desired level over the lifetime of the datacenter. This will also increase the power and cooling requirements in the early part of a life cycle, and both the power generation and the cooling will have to be dimensioned for the maximum values, not for the average values.

It is certainly possible to design a datacenter that will work in space, but there is a very large number of difficulties that will increase the cost both in comparison with terrestrial datacenters and in comparison with existing satellites.

Until a detailed design is done by someone, it is not possible to know exactly how many times more expensive will be a space datacenter, but my opinion, as an engineer with experience in industrial design, is that the cost will be too high to make it worthwhile.

> Well, it can’t use more than it can get from the sun that hits it. So it can’t need to radiate more than that away

You are correct that the first law of thermodynamics dictates the energy, but anyone who has parked a car in the sun will tell you, the temperature where the absorption/dissipation equilibrium is achieved is often incompatible with the survival of the cargo.

edit to your edit:

> Edit: ISS is about 90KW steady state, and the collector to radiator area ratio is about 5:1. Dunno about the mass ratio.

Cool; that's about half the wattage of one modern full-height Nvidia AI rack (172kW) - you need two ISSes to service just 1 rack; extrapolate that to a data center's worth of racks and see if the math is mathing. The ISS is about the size of a(n American) football field.

Well yes, but what matters is how hot that rock gets. Some rocks melt or vaporise in space (see comets).