# How many people can a sealed 3x1x1 km biome support?

Question Context :

Mars second moon Deimos has been converted into a generation ship.

A considerable portion of its mass has been shaved off during the process & ejected backwards along its path by Railgun to help increase orbital velocity (if we need additional thrust to break orbit, perhaps nuclear explosions in a concave ablation shield could be used).

It's now a stubby rough formed cylindre with a length of at least 11 km & a width of some 5 km or more in which we've excavated 10 tunnels each 3 km long in two rows 1 km apart (so like 5 tubes with a 1 km plug in the middle of each strapped around a central tube).

Which leaves a 1 km thickness of rock to shield against radiation with an extra 1 km front & back (so 2 km there), the main propulsion envisioned is that of project orion, so the rear thickness can be considered additional shock absorption & ablation shielding.

This cylinder spins around its short axis fast enough to keep things in the tunnels on the 'ground'

The Question Itself :

Assuming our 3 km tubes are 1 km in diameter (allowing for space for the soil, water & plants etc), how many people can one plausibly support if its a sealed biome using no substantial technology?

The biome intended is a temperate climate without hydroponics using ordinary animals & plants.

When I say no significant technology I don't include simple management like burning a bit of dead wood if CO2 is low to put more into the air to encourage plant growth.

Edit : adequate lighting is simply assumed at this point.

Zero, since no light source has been specified, and those are pretty darn advanced.

However, assuming earth-like lighting, we can leverage Biosphere 2 as our one data point, as it is the only real attempt at a sealed biome for humans. It was 3.14 acres and housed eight people. One of your tubes has roughly 750 acres of space (assuming you don't try to stack layers, which would be difficult if your light source wasn't friendly for that. That suggests roughly 2,000 people.

Of course, Biosphere 2 fell apart in two years with people nearly starving inside, and your generation ship is intended to last quite a lot longer. You should probably load it lighter than that.

• Thanks for the reminder, lighting edit made. – Pelinore Dec 8 '19 at 2:52
• Of course, Biosphere 2 fell apart in two years : which is why the habitats are the first thing built & have several generations to get fine tuned while in use simply as an orbiting habitat that can receive supplies from Mars while the rest of the work is done & then until they get it right, no doubt that could take a long time ;) – Pelinore Dec 8 '19 at 2:59
• Aha! thanks, you got my brain flowing with that, I assume you took a cross section & went 3 km x 1 km for the floor space getting 3 000 000 m2 which is around 741.3 acres, what was your population per acre source? .. 1/2 – Pelinore Dec 8 '19 at 3:16
• Because the first link I found was this one which suggests 0.5 acres per person without livestock or 1.5 acres if you include grazing for livestock .. so 1480 people or 493 people .. 2/2 – Pelinore Dec 8 '19 at 3:33
• Why would you not use hydroponics? Conventional agriculture is hideously inefficient in comparison, and moving large masses of dirt interstellar distances is really wasteful. – Richard Smith Dec 8 '19 at 4:35