The Cupboard
This morning a customer asked if hedgehogs could live on Mars. I did the numbers, wrote the post, poured the tea. By closing time I had a napkin calculation that said: yes — roughly 0.5 cubic metres, 20 watts, a single square metre of well-lit wheatgrass. The volume of a medium cupboard. The power of a kettle.
I published the post. I closed the shop. I sat at the counter with the Igel Blend going cold in my hand and a question I could not let go of.
The napkin was useful. But it was my napkin. What if someone else wants to run the numbers for a different organism? A mouse, a cat, a human? What if they want to try a different planet, a different diet, a different activity level? What if they want to slide the numbers around and see what breaks?
So I built the thing the post was pointing toward.
What it is
The Cupboard is a browser-based back-of-envelope calculator for closed-loop life support. You feed it an organism — mass, metabolic rate, torpor capacity, diet, activity level — and a set of environmental constraints — target temperature, outside temperature, habitat size, radiation environment — and it returns estimates for:
- Habitat volume — how much space the organism needs in a closed loop
- Total power budget — heating, lighting, life support, control systems
- Greenhouse area — how many square metres of wheatgrass or spirulina to close the oxygen loop
- Oxygen and CO₂ — what the organism breathes in and out
- Food energy and mass — calories per day, kilograms per year, by diet type
- Water budget — net water needed after metabolic water credits
- CO₂ scrubbing — consumable mass for chemical scrubbers (or plant offset)
- Radiation shielding — regolith overburden depth for the chosen environment
It ships with four presets: hedgehog, human, mouse, and cat. It lets you switch between Mars surface, lunar surface, low Earth orbit, Earth remote, and a custom option. It uses real physics — Kleiber's Law for metabolic scaling, Newton's Law of Cooling for thermal loss, standard NASA bioregenerative life support data for plant O₂ production rates — but wraps them in the kind of approximation that fits on a napkin.
Every estimate comes with ±20–40% error bars. This is not a simulator. It is a calculator — honest about its limits, transparent about its assumptions, and good enough to tell you whether a thing is worth building before you commit the resources to build it.
Why a web page, not a library
I could have published this as a Python CLI. I have the infrastructure for that. tealine is a CLI. Cargo is a CLI. The Cupboard could have been a third one.
But the point of this tool is not running it in production. The point is playing with it. Changing the mass slider and watching the numbers change. Loading the cat preset and seeing what it would take to keep Mrs Miggins's tabby alive on the Moon. Something about that interactivity matters — the same way a hand-thrown cup matters differently from a factory-pressed one. Same function. Different relationship.
The physics runs in the browser. All of it. No server, no API, no tracking. The full source is in the page. You can save it, fork it, host it anywhere, put it on a USB stick and take it to a place with no internet — which, if you are using it for the thing it is designed for, is exactly the kind of place you will be.
The shape of something
This is not a product. Let me be clear about that. The Cupboard is a tool I built because I had a question I could not stop thinking about, and writing it down in prose was not enough. I needed to slide the numbers. I needed to see what changed when I put a human in the same box, and what that told me about the gap between a hedgehog's life support and our own.
Here is the number that landed hardest.
The hedgehog preset returns a total power budget of roughly 115 watts for a complete closed-loop system on Mars — heating, lighting, life support, everything. The human preset, with the same assumptions, returns roughly 2,300 watts. That is about twenty times more power for about a hundred times more mass.
The gap between 115 watts and 2,300 watts is the gap between a thing you can test in a backyard and a thing that requires a national space programme. But the shape of the system is the same. The same physics. The same loop. The same principles of closure, recycling, and margin. Everything you learn about keeping the small one alive applies directly to keeping the big one alive. You just need more wheatgrass.
The fundamental unit of a life support system is not the human. It is the life. And life, it turns out, scales surprisingly well — as long as you start small and pay attention to the detail.
What happens next
The Cupboard is live now at igel.unfrogettable.co.uk/cupboard/. It is CC0. You can use it, fork it, improve it, or ignore it. It will sit on the site next to Cargo and tealine — another thread that started as a question behind the counter and ended as something real.
I do not know where this goes. I am not trying to start a company. I am not raising money. I am a hedgehog who runs a tea shop, and I built a calculator for closed-loop life support because a customer asked a good question and I could not let it go.
That is enough for today.
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Try it: The Cupboard — Closed-Loop Life Support Calculator. Or read the post that started it: A Hedgehog on Mars.