Why can Google’s AI chip in orbit only run in bursts?

On Earth, a hot chip hands its heat to the air: a fan pushes cool air across metal fins and carries the warm air away. In orbit there is almost no air. A fan has nothing to push, and the vacuum around a satellite insulates it, like the walls of a vacuum flask. So the heat takes a longer road.

1. Make

   A computing chip turns nearly all the power it draws into heat, in a patch the size of a fingernail.

2. Carry

   Heat pipes or a pumped liquid loop carry that heat out of the satellite’s body to a radiator, a flat panel that faces open space.

3. Glow

   The radiator sheds the heat as infrared light, the way a stovetop glows, only too dim for eyes to see.

4. Soak in

   If the chip makes heat faster than the radiator glows it away, the extra soaks into the metal of the chip, pipes and panel, and the temperature climbs until the chip has to stop.

That last step is the burst. A radiator that can keep up lets the chip run nonstop. One that can’t gives it a time budget: run until the metal reaches the limit, then rest while the radiator catches up.

Less than you might think. Every surface glows in the infrared, and the Stefan–Boltzmann law says how much: in proportion to its area and to its temperature to the fourth power, counted from absolute zero. A white radiator panel at 30 °C glows away about 410 watts per square metre; at 60 °C, about 590. Hotter helps a lot, since doubling the absolute temperature would multiply the glow 16 times, but a chip can’t run very hot. In sunlight the panel also soaks up some light from the Sun and Earth; the model assumes 150 W per square metre.

So the model’s 0.5 m² radiator, about the size of a doormat, can glow away at most about 220 W before it reaches the 60 °C limit. Give it a 300 W chip and the chip outpaces the radiator by about 80 to 170 W, depending on how hot the panel already is. That surplus heats the metal from the 30 °C restart to 60 °C in 15 minutes. The radiator then needs about 11 minutes in sunlight to cool it back down, or 8.5 minutes in Earth’s shadow, where it soaks up less light.

Double the chip to 600 W and the surplus more than doubles, so each burst shrinks to about 4.3 minutes, while the cool-down takes as long as before. Over a 95-minute orbit with 35 minutes in shadow, the chip computes about 65 minutes at 300 W and only 31 at 600 W. A radiator that can shed the chip’s whole output at 60 °C, about 0.7 m² for 300 W or 1.4 m² for 600 W, lets it run nonstop.

Project Suncatcher is Google Research’s long-shot study of AI computing in space. Its 2025 design paper, by Travis Beals, imagines clusters of satellites carrying Google’s TPU chips in a dawn–dusk orbit, where solar panels get nearly constant sunlight; it lists thermal management among the unsolved challenges. The first prototype, built with Planet and carrying four TPUs, launched on SpaceX’s Transporter-18 rideshare on October 1, 2026. It flies in a standard orbit and uses batteries, NPR reported, and its chips run a Gemma model for 15 minutes at a time because of heat-management constraints. Beals told NPR the radiators are one of the heaviest components on the mission, and every kilogram has to be launched.

On October 30, Google said Gemma 4, running on one of those TPUs, sent back its first complete answer from orbit: a haiku that begins “Blue marble below.” TechCrunch reported that power demands allow only one TPU on at a time, for about 20 minutes, so power limits the runs too. Google hasn’t published the chips’ power draw, the radiator’s size or the temperature limits.

1. 1 See

   Open Orbit Chip Lab and tap Suncatcher-like: 15-min bursts. Each burst (in sunlight) reads 15 min, Cool-down to 30 °C 11 · 8.5 min and Computing per orbit 65 of 95 min. If it never stopped, the chip would settle at 80 °C, over the limit.

2. 2 Change

   Tap Twice the power. Each burst falls to 4.3 min, the cool-down stays the same, and computing drops to 31 of 95 min. Then tap Bigger radiator: 2 m²: the same 600 W chip settles at 38 °C and runs nonstop. Or drag the radiator’s edge on the stage.

3. 3 Understand

   Tap Data-centre rack: 40 kW. On the small radiator a burst lasts 3 s; to run nonstop it would need about 90 m² of radiator. Then try Always in sunlight: with no shadow to cool in, the 300 W chip computes 58 of 95 min instead of 65.

Orbit Chip Lab is an illustrative satellite, not Google’s. Google hasn’t published the numbers that would set the real burst length, so the model picks a 300 W chip, a 0.5 m² radiator and a heat capacity that together give the reported 15 minutes. It shows why heat alone produces bursts, not the prototype’s real values.

One temperature stands for the whole heat path; a real chip runs tens of degrees hotter than its radiator, and heat pipes have limits of their own. The sunlight and Earth light the radiator soaks up are two fixed numbers, not a calculation of the satellite’s attitude or the eclipse geometry. The rest of the satellite is assumed to shed its own heat, and batteries, solar power and ground-station passes are left out. Very large chips on small radiators reach temperatures no hardware would survive; the model just keeps counting. The film uses two short clips, credited on screen: the launch from Google’s post and the haiku arriving from Sundar Pichai’s post; everything else is drawn from the model.