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

Model. One temperature T stands for the chip, its cold plate, the heat pipes and the radiator: C dT/dt = P − A(εσT⁴ − q). P is the chip's power while it computes, all of which becomes heat. The radiator of area A glows from one face with emissivity ε = 0.85 (white radiator paint) and σ = 5.67 × 10⁻⁸ W/m²K⁴, so each square metre glows away about 410 W at 30 °C and 590 W at 60 °C. q is the sunlight and Earth light the radiator soaks up: 150 W/m² in sunlight and 60 W/m² (Earth's infrared only) in Earth's shadow, both assumed. The heat capacity C = 1,430 J/K plus 4,400 J/K per m² of radiator (about 1.6 kg of aluminium for the chip, cold plate and pipes, plus a 4.9 kg/m² panel) was tuned so that a 300 W chip on a 0.5 m² radiator, starting at 30 °C in sunlight, reaches the 60 °C limit in 15.0 minutes, the burst length reported for Google's prototype. The chip stops at 60 °C and starts again once the radiator has cooled it to 30 °C. An orbit takes 95 minutes, with up to 36 minutes in Earth's shadow at 500 km (the Earth's shadow control).

Why bursts. In a vacuum no air touches the chip, so fans and convection do nothing; heat leaves only as infrared light from the radiator, εσT⁴ per square metre. If the chip makes more heat than the radiator can glow away below the limit (here at most 222 W for 0.5 m² at 60 °C, against 300 W), the surplus warms the metal and the temperature climbs. A burst lasts roughly CΔT ÷ (P − the heat radiated): double the power to 600 W and it falls from 15 to 4.3 minutes, while the cool-down (about 11 minutes in sunlight, 8.5 in shadow) stays the same. A radiator big enough to shed P at 60 °C, P ÷ 443 W/m² in sunlight, lets the chip run nonstop: 0.68 m² for 300 W, 1.4 m² for 600 W, and about 90 m² for a 40 kW data-centre rack, a third of a tennis court. Google lists thermal management among the significant engineering challenges that remain, and Travis Beals, who leads Project Suncatcher, told NPR the radiators are among the heaviest components of the current mission.

Google's satellite. Project Suncatcher, announced by Google Research on 4 November 2025, studies constellations of solar-powered satellites carrying TPUs in a dawn–dusk sun-synchronous orbit with nearly constant sunlight. Its first prototype, built with Planet and carrying four TPUs, launched on SpaceX's Transporter-18 rideshare on 1 October 2026; it flies in a standard orbit and uses batteries. NPR reported that its chips run a Gemma model for 15 minutes at a time because of heat-management constraints. On 30 October 2026 Google said Gemma 4, running on an orbiting TPU, sent back its first complete answer, a haiku. TechCrunch reported that power demands allow only one TPU on at a time, for about 20 minutes, so power limits the runs too. Google has not published the chips' power, the radiator's size or the temperature limits, so the satellite here is illustrative: it shows why heat alone produces bursts, not this satellite's real numbers.

Limits. One temperature stands in 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 surroundings are two fixed numbers rather than a calculation of the satellite's attitude, Earth's reflected light or the eclipse geometry. The rest of the satellite is assumed to shed its own heat, and batteries, solar power and ground-station passes, which also limit real runs, are left out. The radiator's mass grows with its area, but launch cost is not modelled. Above a few square metres the drawing is not to scale, and very large chips reach temperatures no real hardware would survive; the model just keeps counting.

The pictures. The satellite, Earth, fans and graphs are drawn in code. The film also shows two short real clips, picture only, each credited on screen: the Falcon 9 launch of 1 October 2026 from Google's post (@Google), and the ground-station terminal as Gemma's haiku arrives, from Sundar Pichai's post of 30 October 2026 (@sundarpichai). The numbers come from the model.

Sources: Google Research, Exploring a space-based, scalable AI infrastructure system design (Travis Beals, 4 Nov 2025); NPR, Google launches Project Suncatcher, a step towards AI data centers in space (1 Oct 2026, corrected 2 Oct); Google, Project Suncatcher's first response from orbit (30 Oct 2026); TechCrunch, Google's first data center satellite is online and writing poetry (30 Oct 2026); Wikipedia, Stefan–Boltzmann law and Spacecraft thermal control.