1. The soldier who outlived the war

Joe Haldeman’s The Forever War is full of soldiers traveling between stars and returning to civilizations they no longer understand. The only constant is the ship: a self-contained world that must generate its own power and recycle its own resources. The desktop is not a warship, but it has the same problem. It must make its own power in a place where extension cords do not reach.

Entry 186 listed the desktop’s first attachments. This entry estimates how much power they need and how to provide it.

2. Payload power demand

Start with the attachments:

  • Compute cluster: 0.5–2 kW continuous, depending on size and workload.
  • High-rate communications: 0.2–1 kW continuous, more during high-rate downlinks.
  • Sensor suite: 0.1–0.5 kW average, with peaks during imaging.
  • Manufacturing workshop: 0.5–2 kW when active, near zero when idle.
  • Keeper tug: charged from the desktop, perhaps 0.5 kW during charging.

Adding these gives a payload power demand of roughly 2–6 kW continuous, with short peaks to 8 kW or more when manufacturing and communications coincide.

3. Housekeeping power

The desktop itself needs power: avionics, thermal control, attitude determination and control, robotics, and lighting if there are human visitors. Estimate 0.5–1.5 kW continuous.

Total continuous demand: 3–7.5 kW. With margin and peak handling, the power system should be sized for 10 kW or more.

4. Solar array sizing

At LEO, a solar array with modern cells produces roughly 150–250 W per square meter depending on cell type, pointing accuracy, and degradation. To deliver 10 kW after losses, the desktop needs roughly 50–70 square meters of array.

That is large but not unprecedented. The International Space Station’s arrays are much larger. Commercial communications satellites in GEO often carry arrays in the same range. The desktop would likely use deployable arrays that unfold after launch.

5. Energy storage

LEO has eclipse periods of up to 36 minutes per orbit. Batteries must carry the load during those periods. For 7.5 kW continuous demand, that is about 4.5 kWh per eclipse. With depth-of-discharge limits and margin, a 10–15 kWh battery pack is reasonable.

Lithium-ion is the current standard. By the time the desktop flies, lithium-sulfur or solid-state options may offer better specific energy.

6. Thermal implications

Generating 10 kW of electricity means rejecting roughly the same amount as waste heat, plus any heat generated by the payload. This is a major thermal design driver. The desktop will need large radiators, probably on multiple sides, and careful thermal routing from attachments to radiator surfaces.

The next entry will look at this directly.

What this changes

  • The desktop’s continuous power demand is estimated at 3–7.5 kW, with peaks to 10 kW or more.
  • A 10 kW-class solar array would require roughly 50–70 square meters of modern cells.
  • Energy storage of 10–15 kWh is needed for LEO eclipse periods.
  • The next leisure entry will estimate the desktop’s thermal budget.