Biosphere 2

Earth's biosphere performs this function effortlessly on a planetary scale, but replicating even a fraction of that capability in a sealed vessel requires extraordinarily sophisticated ecological engineering.

The Biosphere 2 experiment in the early 1990s demonstrated both the potential and the difficulty.

The sealed facility in Arizona struggled to maintain atmospheric oxygen levels and experienced ecological instabilities that threatened the project within its first two years.

A generation ship would need to solve those problems permanently, with no option to open a window.

You just reminded me of an experience I had with my parents.

We went on a little road trip, maybe 25 years ago, we went to Biosphere 2 in Tucson.

And one of the experiences we had was, um, we were on a tour in the dome.

And the guide said that the experiment was successful, except for one thing.

The most ambitious attempt to build a closed ecological system on Earth ended in a lesson so stark that its implications still haunt life support engineers.

Biosphere 2 was constructed in the Arizona desert in the late 1980s.

It enclosed approximately 1.3 hectares under glass and steel, creating an airtight facility containing multiple simulated biomes including rainforest, ocean, savannah, marsh and desert, along with an agricultural area designed to grow food for a crew of eight people.

The structure was sealed in September of 1991, with its crew inside.

Interpersonal conflict became severe enough to impair cooperation on tasks critical to the experiment's survival.

The second mission, conducted in 1994 with a different crew, ended prematurely amid management disputes and allegations that the closure protocols had been violated.

Biosphere 2 was not a small experiment.

It was a massive, expensive, carefully engineered facility built on the surface of Earth, where gravity was free, sunlight was abundant, structural integrity was guaranteed by a firm foundation, and the ambient environment outside the glass was breathable air at normal pressure and temperature.

Consider what humanity has actually achieved in closed ecosystem experiments.

The most famous attempt, Biosphere 2 in Arizona, sealed eight people inside a large glass structure in 1991 with the goal of surviving for two years using only recycled air, water and food.

The experiment failed on almost every measure.

Oxygen levels crashed and had to be replenished from outside.

It may become solvable in centuries or millennia, it may not.

So the verdict, honestly delivered, depends on which of these clocks we assume the ship can master.

If we assume only the technology we have actually demonstrated, as of the current decade, the 98% water recovery of the International Space Station's life support system, the imperfect closed ecosystems of Biosphere 2 and Melissa, the decades-long operational lifetimes of Voyager-class spacecraft, The reference starship, even with generous reserves, could last perhaps a few decades to a few centuries before critical systems began to fail beyond repair.

That is not enough for even the shortest interstellar journey to a nearby star, let alone an intergalactic crossing.

No closed biological system on Earth has ever operated without external inputs for more than a few years.

Biosphere 2, the most ambitious attempt to create a sealed self-sustaining ecosystem, famously struggled with oxygen depletion, species die-offs, and social conflict among its crew within its first two-year closure experiment.

ESA's MELISA program, which aims to develop a closed-loop biological life support system for space, has been under development for decades and has not yet achieved full closure even in ground-based laboratory conditions.

The lesson from every attempt at closed system life support is the same.