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SpaceX has now put real numbers on it — AI1, an orbital AI-compute satellite with a ~150 kW peak payload cooled by a 110 m² radiator. Google's Project Suncatcher and startups like Starcloud want to run AI on 24/7 solar in orbit too. Serious infrastructure, or a billionaire's daydream, and if it's real, when does it go mainstream? Run the same GPU rack in space and on the ground, find the launch cost where orbit actually wins on $/GPU-hour, then meet the catch: the binding constraint isn't lift cost, it's the mass of the radiator you must launch to dump the heat.
Build the same compute on the ground and in orbit, then see which pays back, and when.
+ grid power $911M/yr, every year
power $0/yr · re-launch compute $7.3B/yr
t0 build cost for equal useful compute. Earth runs 7,143 racks; orbit flies 7,937 (1.11× for radiation redundancy). Earth trades a cheaper build for a recurring power bill; orbit front-loads the launch to erase it.
The launch price isn't a fixed slider, it's falling ~9%/yr over the long run, ~22–28%/yr in the reusability era. Project it forward and find the year it drops below your breakeven (the green line, driven by every other assumption on this page).
The honest case for orbit isn't a lower $/GPU-hour, it's that on Earth you increasingly can't build at all. NIMBY zoning, water and noise fights, and 7-year grid-interconnect queues mean compute is becoming speed-constrained, not chip-constrained. GPUs bought to sit in a queue depreciate before they earn.
N. Virginia/PJM up to ~7 yr; Dublin moratorium to 2028; new transmission lines 10–15 yr. Orbit deploys in ~12 months.
Two levers move almost everything: how cheap launch gets, and how heavy cooling stays. Start from a preset, then push the dials and watch the verdict above move.
Sun-synchronous dawn-dusk orbit stays in continuous sunlight, the steelman for space, no battery mass (Google Suncatcher's choice).
Core economics are workload-agnostic (launch vs radiator). Turn on a workload to add the laser-downlink penalty, illustrative and editable in Assumptions.
Falcon 9 today ≈ $2,720/kg; Starship targets $10–50/kg. Drag down to find the breakeven.
ISS heritage ≈ 291; advanced integrated panels ≈ 10; idealized droplet radiators ≈ 0.7. In a vacuum you can only shed heat by radiating it.
At today's radiator setting the heat-rejection hardware is 1,400 kg, 41% of launch mass, often more than the rack itself. Launching the whole stack costs $9.18M per rack at $3k/kg. The obsolescence split matters: the 1,360 kg of compute is re-launched every 4 yr, but the 2,016 kg bus (solar, radiator, structure) is launched once per 12 yr.
In a vacuum there is no air or water to carry heat away — you can only radiate it. How much radiator area that takes is set by two design choices, and SpaceX's AI1 pushes both to the limit: how hot you run the skin, and whether you fly edge-on to the Sun.
On Earth a chip sheds heat into air and water (convection + conduction). In orbit the only exit is thermal radiation — here for a panel radiating from both faces:
Rejection scales with the fourth power of skin temperature. Run the panel cool and let it face the Sun and, after the ~1,361 W/m² solar wash plus Earth's albedo and ~280 K IR, it nets only ~350 W/m². Run it hot — AI1's ~65 °C skin — and fly it edge-on so each face sees deep space, not the Sun, and the two faces together reject ~1,400 W/m² (2 · 0.95 · σ · 338 K⁴ ≈ 1,408).
That ~4× swing is the whole ballgame. A 140 kW rack sized the naive way needs:
But AI1 rejects its 150 kW peak in just 110 m² (≈1,360 W/m² net) — about 3.6× smaller than the naive sizing. Credit where it's due: that hot, double-sided, edge-on radiator is the core move that turns “too big to launch” into a real satellite. The price is thermal margin — silicon near ~90 °C, a hair under its ~105 °C throttle — so it leans on high-reliability pumps with little headroom.
Even at 110 m², the panel is still a meaningful solar sail at low altitude — drag that demands station-keeping propellant — which is why a higher, edge-on dawn-dusk orbit (where it flies edge-on anyway) is the sane default. Note this is radiator area; the launch mass per kW (the slider above) is a separate lever, and the one that actually drives the economics.
What AI1 actually shows. SpaceX's announced bird is, almost to the kilowatt, one rack per satellite (~120 kW average, 150 kW peak). The headline isn't the solar wing — it's the radiator. At a conservative ~350 W/m² you'd size the heat-rejection panel for a 150 kW load at ~430 m²; AI1 does it in 110 m². The trick is pure Stefan-Boltzmann: run the skin hot (~65 °C) and fly it edge-on so both faces see deep space instead of the Sun, and rejection jumps ~4× to ~1,400 W/m². The cost is thermal margin — silicon near 90 °C, just under its throttle — but it is what turns “too big to launch” into a real satellite. That is the engineering to respect.
Cheap rockets are necessary but not sufficient. Drop launch cost to Starship's target and orbit still has to launch, and then never service, a radiator that, with today's tech, can outweigh the computer it cools. The orbital thesis really rests on two bets stacked on top of cheap launch: a 10–30× lighter radiator and hardware that survives years without a technician. Defaults assume the kindest case: a dawn-dusk sun-synchronous orbit with no batteries; switch to a 30° LEO and battery mass plus an oversized array make it worse. The obsolescence trap is the quiet drag: GPUs age out every few years and must be re-launched, even as the bus lives on. Where it gets interesting is power-constrained grids: push Earth electricity up (or assume you simply can't get the megawatts on the ground) and free 24/7 solar starts to pay for the launch.
At facility scale the deal is a swap, not a saving: orbit converts a recurring grid bill (opex) into an upfront launch (capex), and pays it back only if the avoided power outruns the re-launch toll of replacing GPUs every few years. So the payback flips on launch price: cheap enough and orbit wins from day one; expensive enough and, at today's prices, the power bill is unlikely to repay it. The quiet, under-priced advantage isn't dollars, it's time-to-power: a multi-year grid-interconnect queue on the ground versus sunlight that's available the day you arrive.
Three physics taxes this model now lets you turn on, and two it leaves as caveats. Radiation: cosmic rays flip bits and corrupt training gradients, so orbit spends compute on redundancy; dial the overhead from ECC-plus-checkpoint (~10%) to full triple-modular redundancy (67%) and watch the breakeven move. Interconnect: frontier training is synchronous and bandwidth-bound; inter-satellite lasers can't carry it, so space is structurally an inference and edge tier, not a training one. Heat as area: the radiator isn't just mass, it's ~300 m² per 120 kW rack, a sail that drags in low orbits and needs station-keeping propellant (our dawn-dusk SSO default sits high enough to soften this; drop to a low LEO and it bites). Two we don't price: the re-entry externality (alumina from burning up refreshed hardware is a live ozone-and-regulatory risk) and the real value driversbeyond cost: grid-bypass, in-orbit edge inference that downlinks only insights, and physical/sovereign security. Net: orbit looks like a specialized premium tier, not a replacement for hyperscale.