A DC Atlas Frontier
Module 4 of 7
The Power Problem
Solar arrays sized per kilowatt, then the eclipse tax: 47% of every orbit in Earth's shadow forces battery mass and array oversizing. What 40 MW continuous actually needs in the sky.
Built on published aerospace engineering figures and DC Atlas's facility data.
Power is where the orbital pitch is on its firmest ground, so it deserves a fair hearing. Put a platform in a dawn–dusk, sun-synchronous orbit and its solar panels ride the terminator, in near-continuous sunlight, above the clouds and the atmosphere that steal a third of the energy on the ground. The sunlight is stronger — the solar constant above the atmosphere is about 1,360 watts per square metre — and it almost never stops. For an always-on load like AI training, that genuinely removes the intermittency penalty, the expensive problem of storing solar energy overnight, that makes terrestrial renewables costly. This is the real kernel inside the hype, and it is why the idea attracts serious engineers rather than only hucksters.
Then you size the array, and the scale reasserts itself. Solar panels convert only so much sunlight per square metre. The best modern roll-out arrays — the kind NASA recently added to the ISS — produce roughly 170 watts per square metre in orbit; the older rigid panels manage 35 to 50. To feed a 40 MW compute load you therefore need on the order of half a million square metres of the best available array, and two to three million square metres of the ISS-era kind. The ISS itself, whose solar wings are among the largest structures ever flown, covers about 2,500 square metres and generates 84 to 120 kilowatts at a specific power of only 10 to 15 watts per kilogram once you count the structure. A 40 MW data centre needs several hundred ISS's worth of solar wing, every panel of it lifted from the ground and unfolded in space.
The eclipse tax, over one orbit
Solar output vs. IT load across a single 94-minute low-orbit pass
Illustrative, for a ~550 km orbit. The array is sized to ~92 MW — over twice the 40 MW load — so that during the ~50 sunlit minutes it can both run the facility and recharge the batteries that carry the full load through the ~44-minute eclipse, when solar output is zero.
That flat load line through the dark half of the orbit is the whole problem in one picture. An AI cluster cannot pause its training for 44 minutes out of every 94, so something has to carry the full 40 megawatts while the panels make nothing. That something is a battery bank sized to run the entire facility through the eclipse — roughly 30 to 40 megawatt-hours, weighing 180 to 250 tonnes at today's best cell energy density — and a solar array oversized by a factor of 2.2 to 2.5 so it can both power the load and refill those batteries during the sunlit stretch. Every one of those tonnes launches on top of the radiator field from Module 2, and the batteries themselves degrade and must eventually be replaced, in orbit, where nothing can be replaced.
| Requirement | Basis | Result for 40 MW |
|---|---|---|
| Solar array area | ~170 W/m² (modern roll-out) to ~40 W/m² (ISS-style) | ~0.5–0.6 M m² (best case) to ~2.5–3 M m² |
| Eclipse fraction | ~44 min of every ~94-min orbit in shadow | ~47% of every lap dark |
| Array oversizing | Run the load AND recharge in the sunlit half | ×2.2–2.5 nameplate → ~90–100 MW of array |
| Battery energy | ~0.7–1.0 kWh per kW of continuous load | ~30–40 MWh |
| Battery mass | ~150–200 Wh/kg (state-of-the-art Li-ion) | ~180–250 tonnes |
Add the columns and the shape of the machine is clear. To run 40 megawatts of computers in orbit you fly a radiator field of 60,000-plus square metres, a solar array of half a million square metres, and a couple of hundred tonnes of batteries — and the computers themselves are almost an afterthought in the mass budget. The free sunlight is real. It is also the smallest of your problems, because you have to build a power station and a radiator farm in orbit to use it, and then, as the next module shows, you have to keep the whole thing running with no one on site to change a part.
Questions this module answers
- Isn't solar power free and continuous in space?
- Nearly. In a sun-synchronous orbit sunlight is near-continuous, which is the pitch's strongest point. But the arrays are enormous (around half a million square metres for 40 MW) and the sun still sets on every orbit.
- What is the eclipse problem?
- A low-orbit platform spends about 47% of every 94-minute orbit in Earth's shadow, which forces roughly 180 to 250 tonnes of batteries and a solar array oversized by 2.2 to 2.5 times.