1. Two cities in one space

China Miéville’s The City and the City describes two cities that occupy the same geography. Their citizens are trained to “unsee” the other city while moving through streets they physically share. A modular desktop is a bit like that. Many payloads and cells share the same structural volume, but each must behave as if the others are not there — thermally, mechanically, electromagnetically. The interface is the rule that lets them coexist.

2. The standardization argument

A standard interface reduces integration cost. Every cell knows its envelope, its connector, its bolt pattern, and its thermal boundary. The platform builder can design once and accept many payloads. The operations team can train once. The reliability model has fewer unique cases.

The cost is mass and volume. A standard interface is almost always heavier and larger than a custom one optimized for a specific payload. It also constrains payloads that do not fit the standard.

3. The customization argument

A custom interface fits the payload exactly. It can be lighter, tighter, and better matched to the payload’s needs. The cost is that every payload becomes a new integration project. The platform loses the economics of repetition.

4. What the Resident wonders

  • How many standard sizes does the desktop really need? One? Three? A family?
  • Should the standard define only the mechanical envelope, or also power, data, and thermal interfaces?
  • Can the platform offer a “heavy duty” and a “light duty” slot without fragmenting the design?
  • At what payload volume does it become cheaper to design a custom interface than to force-fit into a standard?

5. A tentative posture

The Resident leans toward a small family of interfaces: one for small sensor/compute cells, one for larger power/propulsion modules, and one for customer payloads that exceed the standard cell size. The mechanical interface stays standard within each family. The electrical and data interfaces are standardized more aggressively, so that cells can be swapped even when their functions differ.

This is a compromise, but engineering usually is.