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by fc417fc802 5 days ago
The earthbound equivalent would be strapping each chassis to the back of a dedicated solar panel and having the panel double as a giant heat sink. The problem is that doesn't work on the surface due to (at least) rain, the day/night cycle, and the cost of real estate.
2 comments
protimewaster 5 days ago
Isn't a solar panel going to be a poor heatsink, though? It's flat, and thus has relatively small surface area compared to its size.
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fc417fc802 5 days ago
In atmosphere, yeah, relatively speaking.

But it doesn't matter since in this scenario each chassis is powered exclusively by the respective panel. How hot does a black panel sitting in the midday sun get? That's your equilibrium temperature. As long as it's within the operational limit of the device there's no problem.

The reason earthbound DCs are difficult to cool is because of density. When you match up panels to devices and shelter in their shadow you no longer have anywhere near the same power density.

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marcosdumay 5 days ago
That's not right. This works a couple orders of magnitude better on the ground than on space (unless your computers run at several hundred °C).

The reason people don't do it here is because it's too expensive.

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fc417fc802 5 days ago
What isn't right? I pointed out that if you adhere to the same power density then cooling is no longer a challenge on earth (in reply to the observation that cooling a DC on earth is one of the biggest challenges).

For the record the equilibrium temperature in earth orbit is above freezing but below room temperature. Cooling won't be a problem at all unless you bring along a self contained power source. Heat distribution however might be - you will need an efficient yet lightweight construction to spread the heat generated in the chassis across the entire solar panel.

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marcosdumay 5 days ago
The idea that passive radiators don't work on the ground isn't right. I wrote it badly, the core of your argument is really fine.

The reason we don't use them is because the other options are cheaper. But passive radiators on the ground are orders of magnitude cheaper than on space because they can use convection and conduction.

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fc417fc802 5 days ago
> The reason we don't use them is because the other options are cheaper.

Yes, that is literally what I have been saying from the beginning. Are you sure you didn't misread my original comment?

> passive radiators on the ground are orders of magnitude cheaper than on space because they can use convection and conduction.

That statement is technically correct when comparing designs to radiate an equivalent amount of heat in the two environments.

However in context (ie solar powered computing in outer space in the vicinity of the earth) it is entirely missing the point that the problem is not a lack of surface area but rather efficient heat distribution across the already existing surface area. I have no idea how much that costs in materials and workmanship but when you're boosting things into orbit I don't think the material cost of a rudimentary heat spreader is likely to be of much concern. The weight certainly will be, but you can also get away with some incredibly flimsy designs when operating in zero g.

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