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Cooling in space: the radiator problem

On Earth, air and water carry heat away with fans, chillers and cooling towers. In space there's no air, so the only way out is to glow: heat leaves as infrared light. Power out = emissivity × σ × T⁴ × area. Hotter panels shed far more (T to the 4th power), but chips need to stay cool.

Radiator temperature

60 °C

Best case: a perfect two-sided panel that absorbs no sunlight or warmth from Earth. Real designs need more, and NASA studies find radiators can be over 40% of a power system's mass. The small square = 1 football field.

The latest proposals (plans, not yet proven at scale)

• Starcloud: lightweight deployable radiators, aiming for far less mass per watt than the Space Station's. Its long-range concept pairs kilometer-scale solar arrays with matching radiators.
• Google's Project Suncatcher: a test satellite carrying AI chips, moving heat through heat pipes and solid materials to radiators, with no moving parts.
• The common design: two-sided panels held edge-on to the sun, fed by heat pipes or pumped loops, run as hot as the chips allow.

Why it matters: cooling is one of the three hard problems, alongside launch cost and radiation. Follow it on Road to Orbit.

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How much of the sun do we use?

The sun's power, step by step (TW = a trillion watts; bar length = number of digits in the watts, a log scale)

We run our whole civilization on a sliver of a sliver. That's not a limit, it's headroom: the biggest untapped opportunity we know of, and more of it gets captured every year.

Where AI may go next (our forecast)

If energy is what limits AI, then the optimizing move is to go where the energy is. Sunlight per square meter grows as you move closer to the sun: at half Earth's distance, 4× as much. So we expect compute to follow the sun outward from Earth: first to orbit, then, over decades, onto infrastructure even closer to the sun than Earth is, which people and AI will build together. We think it's likely because it's what the physics rewards.

What could slow it: closer to the sun, cooling gets harder (see Radiators); signals take minutes to reach Earth; and everything has to be launched or built in space.

Approximate figures: the sun's output ~3.8×10²⁶ W; Earth intercepts ~1,361 W/m² over its disc; world electricity ~31,000 TWh a year, ~7% of it solar (2024). Follow the road on Road to Orbit.