Long duration life support

Part of my series on countering questionably common misconceptions in space journalism.

While humans evolved in Africa, they have proven quite versatile and can inhabit perhaps 10% of the Earth’s total surface with a minimum of fuss. That is, neolithic technology is adequate to support human populations anywhere on Earth that isn’t ocean, an ice sheet, above 18,000 feet of altitude, or incredibly hot or dry.

That isn’t a dig at neolithic technology. Brilliant humans have existed since the beginning and staying alive back then was much harder than it is now. What I mean is that neolithic technology can be encompassed and transmitted by a relatively small group of specialists, while most people who work on, say, computer technology, have never and will never even meet each other.

Over time, and especially since the enlightenment and industrial revolution, advanced technology has permitted humans to live in steadily more hostile environments, with greater densities, and more comfortably. Since 1958 there has been a permanent human presence at the south pole and since 2000, in space. Technology exists to provide life support, or to supplement existing capabilities. As a particularly concrete example, the aqualung permits SCUBA divers to breathe under water, enabling extended (though not indefinite) occupation of shallow water.

Let’s cut to the chase. A common criticism of ambitious space exploration plans, such as building cities on Mars, is that life support systems (LSS) are inadequate to keep humans alive, ergo the whole idea is pointless. As an example, the space shuttle LSS could operate for about two weeks. The ISS LSS operates indefinitely but requires regular replenishment of stores launched from Earth, and regular and intense maintenance. Finally, all closed loop LSS, both conceptual and built, are incredibly complex pieces of machinery, and complexity tends to be at odds with reliability. The general consensus is that the sort of LSS required to nourish a generation ship to fly through space for millennia is beyond our current capabilities.

No matter how big the rocket, supplies launched to Mars are finite and will eventually be exhausted. These supplies include both bulk materials like oxygen or nitrogen, and replacement parts for machinery. This doesn’t bode well. Indeed, much of the dramatic tension in The Martian is due precisely to the challenges of getting a NASA-quality LSS to keep someone alive for much longer than originally intended.

I’m not an expert on LSS by any means, but I will include here a brief summary of what they have to do to keep the squishy humans alive in space.

Humans will live on some sort of base or habitat which contains volume pressurized with gas. On Earth, we breath a mixture of nitrogen and oxygen, with bits of argon, water vapor, CO2, and other stuff mixed in. The LSS has to scrub CO2, regenerate oxygen, condense water vapor evaporated by our moist lungs, and filter out contaminants that are toxic, such as ozone and hydrazine.

With breathing gas sorted out, humans also drink water, consume food, and excrete waste. For extended habitation, these needs also need to be addressed by the LSS.

On Earth, these various elemental and chemical cycles are produced, and buffered by, the immensely large natural environment. I don’t think anyone thinks that a compact biological regeneration system is adequate to meet the needs of a growing city on Mars. Biosphere 2 had a really good go at this and failed for a variety of reasons. One major one was complexity. If the LSS depends on the good will of tonnes of microbes, most of which are undescribed by science, it is very easy to have a bad day.

The alternative is a physical/chemical system. Much simpler, it employs a glorified air conditioning system to process the air and recycle/sanitize waste products. Something like this exists on every spacecraft, and submarine, ever built. The difficulty arises when a simple, robust machine that is 90% efficient is asked to perform at 99.999% efficiency.

There is a third way, at least for cities on Mars or the Moon.

A mostly closed loop LSS is necessary during transport, but it doesn’t have to operate indefinitely. Flights to Mars will take about 6-8 months, which is within the realms of reliability engineering. Additionally, all flights will have with them substantial cargo and fuel/oxidizer, which can be used as feedstocks for replenishment.

Once on the surface, there is an entire planet of atoms ready to harvest. Rocky planets such as the Earth or Mars are, to a physicist, a giant pile of iron atoms encapsulated by a giant pile of oxygen atoms, with other stuff in the gaps. Nearly all rocks, plus water, contain more oxygen than any other element. The Moon and Mars have a lot of water if one knows where to look. Nitrogen is another issue but does exist in the Martian atmosphere. The upshot is that the LSS on Mars doesn’t have to be closed loop. It can depend on constant air mining or environmental extraction to make up for losses, leaks, and inefficiencies. The machinery can be relatively simple, robust, and easy to maintain. The ISS LSS is, after all, 1980s technology at best.

This blog isn’t the place for a lengthy conversation on Martian agriculture, but I am reasonably certain that plants can be grown there. On the other hand, food requirements are something like 200 kg/person/year, which is quite a long way down the list in terms of both mass and complexity of production. In the initial decade of Mars city development I expect that the bulk of people’s caloric intake will be imported, though some fresh food will be grown locally.

No life support system miracles are required to keep humans alive on Mars in the near future.


8 thoughts on “Long duration life support

  1. A decade is much longer than I would have guessed, for the bulk of calories to be imported. Bulk calories aren’t that complicated, as chemicals. Organic chemistry is an incredibly versatile source of industrial materials. Its feedstock is air and water. We need to do it at a basic level to refuel the rockets.

    If I were planning out the development of a Martian city to demonstrate feasibility, I would import food for quite a while. Budget N tons of transport and N*P dollars. Double it so that you don’t have to worry about whether you got it exactly right, and move on to the big-ticket items. But if I were actually one of the legion of people actually making budget decisions, I think I would divert some of the capacity of the chemical factories to make acetate and ammonia, and feed it to microbes.


      1. Melting some ice is definitely in the first set of stuff to. Or maybe we won’t put a pressure canopy over it, so we would be vaporizing some ice and giving it a surface to recrystallize on. One way would be to set up a large mirror (which can be gossamer thin), and aim it at one patch of slightly icy regolith after another. So yes, ice is certainly getting underway early.

        But one of the reasons for ice to be a priority is rocket fuel. Hydrocarbons are a lot more convenient than H2, and the air is full of carbon. Even if all we make is methane, microbes can eat it, and we can eat them. Why wouldn’t we?

        If we had to do everything by hand like some nineteenth century pioneer village, it would make sense to strictly limit what needs to be done. But every hundred kg of food we don’t bring is about fifty kg of machinery we do (if purchase price and transport cost are about the same). Making food instead of bringing it means more machines making steel sooner — and making more of the versatile carbon-based materials.

        What we want to limit is the stuff that requires real-time human attention, and the stuff that requires a shirtsleeves environment. A vat of methane-eating bacteria may need to be monitored, but it can probably be monitored remotely with a light-speed lag from Earth.

        Bacterial goo won’t be all that appetizing, and making appetizing food will require hands-on labor. So our Martians will be eating imported food bulked up with microbial goo for a while.


      2. Bread and cheese is microbial goo! Yum.

        Local manufacture can be prioritized using market mechanisms. Important constraints include both shipping capacity and local labor availability.

        Liked by 1 person

  2. The failure of Biosphere 2 has almost nothing to do with technological or scientific problems, and almost 100% to do with the fact that it was conceived and run by new age fruit-cakes on the level of anti-vaxxer Goop types. You know – people who “know better” than those know-it-all ivory tower science and engineering experts.

    It’s like … you know why that attempt to reproduce Noah’s Ark didn’t work out? The fundamental problem is that anyone trying to do that in the first place has already rejected “mainstream” science and engineering. This rejection of science and engineering will inevitably pervade the entire project, leading to an endless torrent of mistakes on every level.

    Same problem with Biosphere 2. Most notably, there was a huge basic concept mistake of trying to replicate an extremely complex system by just throwing in everything and hoping it’ll somehow work out, rather than try and simplify things down to a limited number of components – something amenable to engineering analysis. Any engineer, of course, would know to try and limit the variables if practical to try and make it possible to analyze. But if you reject “mainstream” engineering, then … well … that’s how such huge basic mistakes can happen.

    Note that after Biosphere 2’s failure, it was donated to new management in academia. Since then, it has actually been used to perform useful scientific experiments. That’s worth noting, considering it’s unlikely any Noah’s Ark replica would have such a useful second career.

    The bottom line is that you really can’t draw any conclusions about CELSS from Biosphere 2.

    Liked by 2 people

  3. Great post Casey, very appropriate now that most of us are learning what it means to live in a bubble and with limited means of resupply. Not a perfect analogy maybe but a step Great post Casey and yes I agree with you Isaac, very appropriate now most of us are learning to live in a bubble and with limited means of resupply. Not a perfect analogy maybe but a step along the way.

    I think another reason for Biosphere 2’s failure was the culture of technologists (especially when they work with plants) see living systems as closed, complex (not complicated / disconnected) and knowable – in this case this lead to life-threatening falls in CO2 and O2. I often see new entrants to the new foods movement who think like this. Most gardeners know that concrete disrupts plant life even in a free-air environment – cement leaching into surrounding soils dramatically altering pH. Many Utopians do not question widely.

    NASA’s CELSS has a lot to teach us. Even just growing a small suite of plants things become so complicated (disjointed; effects arising from unknown causes) when we have to provide everything for plants.

    When I studied the professors worked VERY hard to stamp out any Utopian ideas we had. I have since added not letting the perfect get in the way of the good-enough.

    Liked by 1 person

  4. IMO Biosphere 2 went wrong because they got confused between an experiment and a demo. If they had said “We’ll try it for up to six months and see how it goes” they would have been able to exit early, then correct for the concrete and try again. Instead, they promised everyone they’d stay in for two years right off the bat, so they spent a while breathing 14% oxygen and eventually had to supplement, causing a perception of failure.


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