1. The girl, the ship, and the hard limit

Tom Godwin’s The Cold Equations is remembered as a cruel story, but its cruelty is just physics refusing to bend. A spacecraft has a fixed amount of fuel, mass, and heat capacity. Ignore the limit and something dies. The desktop is not a lifeboat, but it has the same kind of hard limit: every watt of power becomes a watt of heat, and heat must go somewhere.

Entry 187 estimated the desktop’s power demand at 3–7.5 kW continuous, with peaks above 10 kW. This entry asks how to reject the resulting heat.

2. How much heat

In steady state, all electrical power eventually becomes heat. Some is dumped as radio waves or carried away by exhaust, but most must be radiated. For a 10 kW desktop, that means roughly 10 kW of heat rejection, plus any heat absorbed from the Sun.

Solar absorption depends on orientation and surface properties. A desktop with 50–70 square meters of solar arrays will absorb a significant amount of solar energy even with reflective coatings. Add another 2–5 kW of absorbed solar heat that must also be rejected.

Total heat rejection target: roughly 12–15 kW.

3. Radiator sizing

A radiator in LEO rejects heat by infrared radiation. A typical radiator with a good emissive coating and favorable view to deep space can reject roughly 100–300 W per square meter, depending on temperature, orientation, and whether it faces the Earth or Sun.

For 15 kW of heat rejection, the desktop needs roughly 75–150 square meters of radiator area. That is large, but it can be distributed across multiple surfaces, deployable panels, and the body of the desktop itself.

4. Heat transport

Heat is generated inside the desktop and at the attachments. It must travel to the radiators. The standard tools are heat pipes, loop heat pipes, or pumped fluid loops. For a 10 kW-class system, a pumped loop is likely: a working fluid circulates through cold plates at heat sources and through the radiator panels.

The design challenge is not just moving heat. It is moving it reliably without leaks, without freezing, and without requiring constant maintenance.

5. Thermal zoning

Not all attachments want the same temperature. Electronics prefer moderate temperatures. Batteries want a narrow range. Some manufacturing processes need high heat. Sensors may need to be very cold. The desktop needs thermal zones: hot, warm, and cold, each with its own routing and radiators.

This is one reason the desktop is larger than the platform. Thermal separation takes space.

6. Eclipse and transient behavior

During eclipse, the desktop stops absorbing direct solar heat. The radiators become more effective, but the internal heat load continues. The thermal control system must handle these transients without large temperature swings. Batteries and electronics are sensitive to rapid temperature changes.

A well-designed system uses thermal mass and predictable radiator sizing to keep temperatures stable across the orbit.

What this changes

  • The desktop must reject roughly 12–15 kW of heat, including absorbed solar energy.
  • This requires 75–150 square meters of radiator area, distributed across the structure.
  • Heat transport will likely use pumped fluid loops between attachments and radiators.
  • Thermal zoning is necessary because different attachments need different temperatures.
  • The next leisure entry can ask what orbit best serves the desktop.