The Cupboard

A back-of-envelope calculator for closed-loop life support. Enter the organism, the environment, and the constraints — the tool estimates what it would take to keep it alive somewhere far from home. Named after the line in A Hedgehog on Mars: "roughly the same volume and power as a medium-sized cupboard."

All estimates have honest error bars of ±20–40%. This is a napkin, not a simulator. The physics is real but the precision is approximate — exactly the level of confidence you want when deciding whether a thing is worth building before you commit the resources to build it.

Mass (kg)

Hedgehog: 0.5–1.2 kg · Frog: 0.02–0.08 kg · Human: 50–90 kg

Metabolic rate (W/kg)

Resting. Hedgehog: 0.5–1.5. Human: ~1.2

Torpor rate (W/kg)

0 if no torpor. Hedgehog: 0.02

Target temp (°C)

Mammal: 20–30 °C · Amphibian: 16–21 °C

Outside temp (°C)

Mars equator night: −80 to −60 °C

Habitat radius (m)

Sphere radius. 0.5 m ≈ 0.52 m³

Diet type

Affects food mass and greenhouse loop efficiency

Activity level

Environment

Sets pressure, radiation defaults

📦 Closed-Loop Life Support Estimate

How to read this: These are back-of-envelope numbers with ±20–40% error margins. They are sufficient to tell you whether a thing is worth building, not to specify the final system. Every estimate assumes ideal conditions — perfect insulation, optimal plant growth, zero leakage. Reality will be harder. The margin is where the engineering lives.