Life Lessons the Hard Way
The Gas That Doesn’t Leave
Biosphere 2 sealed out the weather. It also sealed out the one thing that was quietly cleaning its air, and nobody noticed until the gas built up enough to threaten the crew’s nervous systems.
Every closed loop has a return leg, and the return leg is where people get into trouble.
Back in September we wrote about nitrogen going into the system in The Workforce Nobody Hired — bacteria in clover roots cracking it out of the air, feeding it to plants, plants feeding animals. That’s the front half, and it works. The back half is the part nobody budgets for. When things die and decay, other bacteria take that nitrogen apart again and send it back to the air as gas. On Earth that closes the circle.
But the bacteria doing that job aren’t tidy. Denitrification doesn’t only produce clean nitrogen gas. A share of it comes back as nitrous oxide.
Outdoors, that’s somebody else’s problem, and the somebody is the sun. Up in the stratosphere, ultraviolet light breaks nitrous oxide apart — it’s the main way the planet gets rid of it, on the order of ninety percent of it.1 Free, continuous, nobody maintains it.
Now seal the loop. Put it under glass — and glass blocks ultraviolet. Biosphere 2 did exactly this, and nitrous oxide built up inside. One interim report put the buildup high enough to reduce vitamin B12 synthesis to a level that could impair or damage the brain.2
That matters because nitrous oxide isn’t inert to people. It interferes with vitamin B12, and B12 damage shows up in your nervous system.
So the punch list item is this: a nitrous oxide scrubber for a sealed habitat. A UV-C loop that does indoors what the stratosphere does outdoors.
And here’s the frustrating part. The technology exists. UV-C lamps are sold everywhere for sterilizing. Nobody has purpose-built one as an atmospheric scrubber for a closed habitat, sized and rated and proven, because nobody’s had to yet.
The same knob as the bees
Here’s what makes this one interesting rather than just another gap on the list: it’s the same knob as the bees.
If your habitat runs on glass and sunlight, you filter out ultraviolet, and two things go wrong at once. The nitrous oxide stops breaking down, and the pollinators can’t find the flowers, because a bee reads a flower in ultraviolet.3 Biosphere 2 got both problems from one decision, and I don’t think anybody saw them as the same decision at the time — we covered the pollinator half of it back in September in Top of the Loop, Bottom of the Loop.
Which is why I don’t think the barrel should have windows at all.
On Mars, build it out of glass — you’ve got sun coming down and you may as well use it. But in a can in orbit, going fully artificial means you specify the light instead of inheriting it. You choose the spectrum. You put ultraviolet exactly where it earns its keep: in the air handling loop to break the nitrous oxide down, and over the crops at whatever level the bees need to work. You control day length. Nothing is left to whatever the glazing happens to pass.
That’s the difference between a greenhouse and a life support system. A greenhouse takes what the sky gives it. A habitat has to be specified.
So: a nitrous oxide scrubber, a UV budget, and somebody to sit down and work out what the bees actually require. None of that is exotic. It’s just work nobody’s done.
And that’s the whole point of this department. We know what happened. We know why. Nobody’s built the fix.
If you see it differently, or you know of work being done on this that we’ve missed, write in.
If you’ve worked with UV-C sterilization, know of a purpose-built scrubber loop, or think we’ve got the bees wrong, we want to hear it.
Come join us. Because we are Star Bound.
John LangEditor
Ideas in Star Bound are published open — take them, build them better. Our open proposal.
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
- NASA, one-dimensional photochemical modeling of biosphere-atmosphere gas transfer — roughly 90 percent of atmospheric nitrous oxide is destroyed via solar photolysis in the stratosphere — https://ntrs.nasa.gov/api/citations/19920004406/downloads/19920004406.pdf ↩
- Kenyon College, “What Went Wrong?” (Biosphere 2 case study) — nitrous oxide reached levels an interim report said could reduce vitamin B12 synthesis enough to risk brain damage — https://biology.kenyon.edu/slonc/bio3/2000projects/carroll_d_walker_e/whatwentwrong.html ↩
- Sciencing, “Eight People Sealed Themselves Into An Artificial Ecosystem In 1991, Then Something Went Very Wrong” — researchers suspect Biosphere 2’s pollinator collapse traced to glass walls blocking the ultraviolet light some pollinators need to find flowers — https://www.sciencing.com/2212232/eight-people-sealed-themselves-into-artificial-ecosystem-something-very-wrong/ ↩
More from Star Bound
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- Cast It or Print ItThree ways to make a hundred thousand habitat panels. What each one buys you, what each one costs you, and where each one belongs.
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- Commission It FirstWe have already run phase one. It cost one man 150 million dollars of his own money, and it very nearly killed the people inside.
- Life in the BarrelO’Neill gave us the barrel in 1976 and got very little of it wrong. What he did not finish was the inside — and the standard the inside has to meet isn’t twenty years. It’s forever.
- Worms: The Backbone of CivilizationWhy the first Martians will need a bucket of worms more than another rocket
- Send the Robots FirstWhy the road to Mars runs through the moon, and why the first lunar miners will never leave Earth
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- Launch the Parts, Not the ShipYou cannot launch a habitat big enough to spin. So you launch a shipyard, and you let the robots build it.
- Built for Earth, or Built for Something Bigger?The tools a colony needs are being perfected right now, by people who say they are building them for us
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- Out the Side of the MountainTwenty miles of vacuum tube under a Hawaiian volcano, and a freight train that never comes back down. What a ground-based mass driver would actually take, and why it exits the flank instead of the summit.
- That’s Not a Rocket, It’s a Freight TrainHow I wired the one on my bench in 1994, the one I drew and never built, and why a mass driver runs on railroad logic, not rocket logic.
- Cold, Vacuum, and a Hundred Thousand JointsWhat geosynchronous orbit does to the ten-inch panels in "A Thousand Garages," starting with the question every steel man asks first — and one thing that article got wrong.
- Mission Watch: September 2026What private enterprise and the agencies actually did this summer, in the order that matters
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