Cooling a data centre on Earth can consume 10 to 30 per cent of its energy budget and millions of litres of water; in orbit, there is no air, no cooling towers, and no river to dump heat into — only vast radiator panels bleeding waste heat away as infrared light into the blackness of space

Keeping a data centre cool on Earth is a surprisingly large part of the job. Cooling can swallow anywhere from a tenth to a third of a facility s entire energy budget, and the thirstiest sites drink millions of litres of water to do it. Move that data centre into orbit and the whole approach collapses. There is no air to blow across the servers, no cooling towers, and no river to dump the heat into. The only way left to get rid of waste heat is to radiate it away as infrared light into the blackness of space, through vast panels. That single fact shapes everything about the idea of computing in orbit.

Every computer turns electricity into heat, and a data centre is thousands of them packed together. Left unchecked, that heat would quickly cook the machines, so a large share of the effort and expense goes not into computing but into carrying the heat away.

The bill is real. Cooling commonly accounts for something in the range of a tenth to a third of a data centre s total energy use, and often more in hot climates. Much of that cooling relies on water, evaporated to carry heat off just as sweat cools skin. A single one-megawatt facility can get through tens of millions of litres a year, and the largest operators consume water by the billions of litres, a growing source of tension where supplies are tight.

On the ground, heat has easy ways to escape. It moves by conduction into cooler materials, by convection as air or water flows past and carries it off, and by evaporation in cooling towers. Every one of those methods depends on having a surrounding fluid, air or water, to hand the heat to.

Space has neither. The vacuum around a spacecraft is not cold air; it is very nearly nothing at all. With no air to convect into and no water to evaporate, and nothing to conduct heat into, the familiar cooling methods simply stop functioning. You cannot fan away heat that has nowhere to go.

There is one mechanism that still works in a vacuum, and only one: thermal radiation….

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Cooling a data centre on Earth can consume 10 to 30 per cent of its energy budget and millions of litres of water; in orbit, there is no air, no cooling towers, and no river to dump heat into — only vast radiator panels bleeding waste heat away as infrared light into the blackness of space