The Box Nobody Tested

Everything I have written in this magazine about living off Earth comes down to one thing: a sealed box that has to feed you and keep you breathing, with nobody coming by to top it off. On the Moon, on Mars, on a station, there is no window to open. Whatever air you have is the air you make. Whatever food you have is the food you grow. If the box drifts out of balance, you don't get to step outside while somebody fixes it.

So before anybody builds that box on another world, it would be a good idea to build one here, seal some people in it, and see what happens.

Somebody did. It was called Biosphere 2, and it taught us more about living in a sealed world than every study ever written, and it taught it the hard way, for a reason every construction hand in the world will recognize the moment they hear it.

Three acres of glass

Biosphere 2 sits in the desert north of Tucson, Arizona. It is a little over three acres under glass, a space frame skinned with laminated panes, with a stainless steel liner underneath so nothing leaks through the ground. Inside they built a rainforest, a savanna, a desert, a mangrove marsh, and an ocean with a coral reef, plus about half an acre of farm and a living quarters for the crew. Two big variable-volume chambers they called the lungs let the air expand and contract with the temperature without blowing out the glass. ¹

It was privately funded. The money came from Ed Bass, a Texas oil heir, and the usual figure quoted is somewhere between one hundred fifty and two hundred million dollars. ² That matters, because it means nobody was answering to a government program office. They built what they wanted to build, and they built it fast.

On September 26, 1991, eight people walked in and the door was sealed behind them. Four men, four women, ages twenty-seven to sixty-seven. The plan was two years: grow all their own food, recycle all their own water and waste, keep the air breathable, and come out the same door in September of 1993 having proved a closed ecological system could carry human beings. ³

They came out on schedule. Almost nothing else went to plan.

The air

The first thing to go wrong was the air, and it went wrong slowly enough that nobody understood it for more than a year.

Oxygen started dropping. Not fast, but steady. Outside air is about twenty-one percent oxygen. Over the first sixteen months inside Biosphere 2 it fell to about fourteen and a half percent, which is roughly the air you'd breathe at thirteen thousand feet. ⁴ The crew got tired. They got short of breath climbing stairs. Sleep apnea showed up. The oldest crew member, a doctor named Roy Walford who was sixty-seven, was worn down enough that he couldn't finish a sentence without stopping for air. ⁵

Now, if oxygen is disappearing from a sealed box, something is eating it, and there is a simple rule about what that something produces. Every time a living thing burns oxygen, it breathes out carbon dioxide. So the missing oxygen should have shown up as carbon dioxide, and the numbers should have matched.

Carbon dioxide did go up. It ran between two thousand and four thousand parts per million inside, against about three hundred fifty outside. ³ But it didn't go up nearly enough to account for the oxygen that was gone. A big share of it had vanished. The oxygen was leaving the air and the carbon dioxide that should have replaced it was going somewhere else. Nobody knew where.

That's the piece to hold onto. The problem wasn't just that the air was going bad. The problem was that the evidence was being hidden, so the people inside couldn't diagnose it.

Where the oxygen went

The answer came from two geochemists at Columbia University, Jeff Severinghaus and Wallace Broecker, and they found it by reading isotopes. Carbon comes in different weights, and where a carbon atom has been leaves a signature in the ratio. They traced the missing carbon dioxide, and it was in the walls. ⁶

Biosphere 2 was built with an enormous amount of concrete, and a lot of it was left exposed inside the sealed volume. Fresh concrete cures for years, and as it cures it pulls carbon dioxide out of the air and locks it up as calcium carbonate. That is a plain fact about concrete, and it happens in every building on Earth. It is only a problem when the building is sealed and the air inside is the only air there is. Severinghaus measured the absorption rate off the structural concrete and worked out that the walls had swallowed something on the order of seven hundred fifty kilomoles of carbon dioxide, give or take a third. Call it in the neighborhood of thirty tons. ^{6 7}

So here is what was actually happening, in order. The designers had loaded the soil with organic matter to make it fertile, especially in the rainforest and savanna. The microbes in that soil went to work eating it, and microbes eating organic matter burn oxygen and breathe out carbon dioxide, same as we do. There was so much food for them that they were burning oxygen faster than the plants could put it back. Then the concrete drank up the carbon dioxide they breathed out, so the readout that should have pointed straight at the soil pointed nowhere. ⁸

The plants, by the way, were fine on carbon dioxide. They had more of it than they knew what to do with. What they didn't have was enough light, because the glass and the space frame cut the sun down more than the designers figured, and the winters were cloudy. ³ The plants were slow, the microbes were fast, and the concrete hid the difference.

What they did about it

They didn't shut down. In January 1993, with oxygen around fourteen percent and the crew visibly failing, the project pumped oxygen in from outside. ⁴ That kept everybody on their feet, and it also ended the argument about whether Biosphere 2 was a closed system. It wasn't, from that day on. They finished the two years and walked out the door on September 26, 1993.

Then, with the crew out and the building empty, they fixed it. Between the first mission and the second, the exposed concrete was coated to seal it, so it would stop taking up carbon dioxide. ⁹ A second crew went in on March 6, 1994. That mission ended early for reasons that had nothing to do with the air and everything to do with the people running the place, but the concrete was never the problem again.

Read that sequence one more time. The fix was a coating. It was cheap, it was known, and it was available on the day the first crew walked in. It was applied after they walked out.

Everything else

The air was the big one, but the box was fighting them on every front.

The farm was about two thousand square meters and it delivered about eighty percent of what the crew needed to eat. The other twenty percent they didn't get. The diet averaged around twenty-two hundred calories a day, mostly vegetarian, with a little milk and meat and eggs from the goats, pigs, and chickens. Everybody lost weight, ten to twenty percent of their body weight, most of it in the first six months. ¹⁰ Two years of being hungry, on top of two years of thin air, while working long days in the fields.

The pollinators died. The hummingbirds and the honeybees went, and once they were gone the plants that needed them went too. Meanwhile the things nobody invited thrived. Ants and cockroaches took over, and one species of tramp ant killed off most of the other insects in the building. Morning glory overran the rainforest. The desert got so humid it stopped being a desert. ^{3 11}

And the people split. Within about six months the eight of them had broken into two camps of four, one side wanting to bring in outside help to keep the science going, the other side wanting to hold the seal at any cost because the seal was the whole point. By the end the two camps weren't speaking. Some of them still weren't years later. ^{3 12}

None of that is unusual for a small crew locked in a hard place. Antarctic stations and submarines have seen the same thing. What's unusual is doing it to a crew that is also hypoxic and hungry, and then being surprised.

What it cost them, and what it bought us

I have spent forty-one years in heavy industrial construction, and a large part of the last thirty on the commissioning side of it. Commissioning is the part of the job that happens after the thing is built and before it is handed over to the people who are going to live with it. You run every system. You put the loads on and watch what the gauges do. You find out what the building actually does, as opposed to what the drawings say it does, and you fix the difference before anybody is depending on it. Nobody gets the keys until it's done.

Biosphere 2 was never commissioned. It was built, and it was sealed with eight people inside, and the building was tested for the first time with the crew as the test load.

If they had sealed the thing empty for six months and just watched the gauges, the oxygen decline would have shown up in the data. The carbon dioxide would have failed to match it. Somebody would have asked where it was going, and somebody would have looked at the walls, because there was a lot of wall. They'd have sealed the concrete, cut the organic load in the soil, added light, and then sealed the crew in. The first mission would still have been hard. It would not have been a rescue.

None of that is a knock on the people who built it. It is the opposite, and I want to be plain about it, because this is a thing that gets said carelessly and Biosphere 2 has taken more than its share of cheap shots.

Eight people walked into a sealed building nobody had ever built before, on the strength of a private checkbook, and closed the door behind them. They stayed two years. They were hungry the whole time, and for sixteen months of it they were breathing the air of a mountaintop, and they kept the farm running and the data coming and they came out the same door on the day they said they would. Ed Bass put up his own money, on the order of a hundred and fifty million dollars of it, for a building that returned him nothing but knowledge. No program office would have approved that schedule and no program office would have taken that risk.

Everything I have laid out in this article, every number and every mechanism, exists because they went first. The concrete, the soil load, the light through the glass, the way a small crew comes apart in thin air — none of that was in a book beforehand. It is in a book now. Every closed habitat anybody builds from here on gets that for free, and they got it by paying for it with their own money and their own two years. Nobody who stayed home learned anything.

That is what going first costs, and it is not a public-or-private question. Government programs have skipped commissioning and buried people for it. Private ones have too. The difference is never who signed the check. It is whether somebody was willing to build the thing at all, and then whether the next crowd is honest enough to read the report.

So put them where they belong. They are not a cautionary tale. They are the foundation, the main bricks in the thing the rest of us are still building on. If they had stayed home we would be standing here with nothing, running those same two years ourselves and finding that same concrete. We owe them, and the way you pay a debt like that is by using what they bought. Their names are on the Pioneers page of this magazine, and they will stay there.

Which brings me to the one thing I want carried forward, and it is the only place I will second-guess anybody. Biosphere 2 was tested for the first time with the crew inside it. Not out of carelessness. Out of being first, with money on a clock and nobody to tell them what the walls would do. But we know now. So the next box gets sealed empty first, and the gauges get watched with nobody's lungs on the line.

On the Moon that costs almost nothing, which is the beautiful part. You cannot send people until the rooms are bored and lined and sealed anyway. There is a year or two in there where the box exists and it is empty. Put the soil in, put the plants and the worms in, close it, and watch it from here. If the oxygen holds flat on its own for six months, launch the crew. If it doesn't, you have found your concrete, and it cost you nothing but time.

Build the box. Seal it. Run it empty. Then move in.

Ideas in Star Bound are published open — take them, build them better. Our open proposal.

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A note on where this comes from. I am not a metallurgist, a spacecraft engineer, or a degreed engineer of any kind. But I am a practical one, with more than forty years in heavy industrial construction: welding, millwright work, hydraulics, mining, and thirty-three years of electrical construction and commissioning on the North Slope of Alaska, in a place that punishes anything built wrong. Much of that time I have worked as a field engineer, which means I am the one standing in front of the equipment when the drawing turns out to be wrong, and the fix has to be made on the spot, with what is on hand, and has to work the first time. Anyone who has done that long enough learns that a lot of engineering gets corrected in the field by people with more experience than the people who drew it. That is the eye I bring to these subjects: not what should work on paper, but what actually gets built, and what breaks. The facts I take from other people are footnoted so you can check them and read further. The ideas built on top of those facts are my own, and I would rather see them knocked down by somebody who knows better than left standing because nobody looked.

Sources

1. Silverstone, S., and Nelson, M., "Food production and nutrition in Biosphere 2: Results from the first mission September 1991 to September 1993," Advances in Space Research 18 (4–5), 1996 — facility description, biomes, the lung chambers, the stainless steel liner. ↩
2. Funding by Ed Bass; the total cost is variously reported between about $150 million and $200 million. Biosphere 2, Wikipedia. ↩
3. "Benchmarks: September 26, 1991: Crew sealed inside Biosphere 2," Earth Magazine — sealing date, CO2 of 2,000–4,000 ppm against ~350 outside, the crew factions, pollinator and insect die-off, the crazy ant. ↩
4. Oxygen from 20.9% to about 14.4% over sixteen months, roughly equivalent to 13,000 feet; oxygen injected January 1993. "Why Biosphere 2 Failed: Oxygen, Food, and Chaos," ScienceInsights. ↩
5. Roy Walford's condition and the crew's breathing difficulty are described in Jane Poynter's memoir, The Human Experiment: Two Years and Twenty Minutes Inside Biosphere 2 (2006), and in contemporary press. ↩
6. Severinghaus, J.P., et al., "Oxygen loss in Biosphere 2," Eos, Transactions AGU 75 (3), 1994 — 21% to 14% over 16 months; microbial respiration of excess soil organic matter; CO2 absorbed by concrete, approximately 750 ± 250 kmol. ↩
7. The conversion from 750 kmol of CO2 to about 33 metric tons is my own arithmetic (44 g/mol). Other summaries quote roughly 26 tons across about 15,800 m² of exposed concrete; the figures agree within the stated uncertainty. ↩
8. Concrete carbonation as the mechanism, and the concealment of the CO2 signal: Biosphere 2, Wikipedia; also "What Went Wrong?", Kenyon College. ↩
9. Concrete sealed between missions; second mission began March 6, 1994. Biosphere 2, Wikipedia. ↩
10. Farm area about 2,000 m², about 80% of nutritional needs, ~2,200 calories/day, 10–20% weight loss mostly in the first six months. Silverstone and Nelson, as in note 1. ↩
11. Hummingbird and honeybee loss, ant and cockroach explosions, morning glory in the rainforest, condensation in the desert. "When Biosphere 2 Became a Grand Experiment in Self-Isolation," History.com. ↩
12. Factions and lasting interpersonal damage: ScienceInsights, as in note 4; Poynter, as in note 5. ↩
13. The commissioning argument, the assessment of the project's contribution, and the "seal it empty first" proposal for a lunar habitat are my own, drawn from a working career in industrial construction and field commissioning. They are not documented positions of the Biosphere 2 project or its successors.