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2017-09-14, 10:27 AM (ISO 8601)
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Using plants inside a vac-suit to produce oxygen
A local(-ish) magazine just published a light-hearted article because they received a letter from a young aspiring engineer. She wants to design a space-helmet with plants inside to give cosmonauts oxygen, but she's not sure how many plants will be needed.
I have zero knowledge about this topic but I highly doubt that this is practically possible. I think it's an extremely awesome idea though. I'm wondering if anyone here has some knowledge that'd be interesting in this context, i.e. how exactly does the whole respiration thing work and could it be reduced to a small isolated system like a spacesuit? Is there actually a way (theoretically or not) to sustainably 'produce' oxygen that can then be delivered directly to whoever needs it? Or does that only make sense in a complex system like the atmosphere of Earth?
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2017-09-14, 11:13 AM (ISO 8601)
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Re: Using plants inside a vac-suit to produce oxygen
I'm sure someone who takes forum threads more seriously than me will come with references and calculations, but I can be lazier and still come up with a way to approximate it:
Plants reject oxygen because they don't need as much oxygen than they get from consuming CO2. So the net amount they release is proportional to the amount of carbon they need to retain. On the flip side, the amount of oxygen you consume is proportional to the amount of calories you burn.
So, to give yourself an idea of how many plants you'd need to recycle your air, think about how many plants, if their entire mass was edible, would produce enough growth to feed you. This is obviously a vague approximation, but I find mental pictures like this useful to get an idea of something's scale.
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2017-09-14, 11:34 AM (ISO 8601)
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- Mar 2007
Re: Using plants inside a vac-suit to produce oxygen
Look at something like this: http://www.wikihow.com/Make-a-Closed-Aquatic-Ecosystem
but hopefully with some idea of the mass of the plants needed vs. the mass of the animals.
You also need a full pressure suit, otherwise bad things happen (I can't see a reason for your lungs not to work without air pressure to your chest, but I suspect I am missing something).
One painful issue with the whole "bring plants into space" idea is delivering the sunlight. The plants need to be kept to near atmospheric pressure levels (so you can breathe the air), and just scaling glass will wind up with the mass scaling with the area (because scaling by volume would block too much sunlight). I suspect that containing the plants in a more spherical (or at least low surface area structure) and lighting them with solar powered LEDs might work better.
If the square/cube issue is solved with solar power, it might work on board the ISS, but I still think it would be too bulky to include in (even already bulky) spacesuits. And all that is for spacewalking: it would never work as a spacesuit on Mars (not to mention that Mars gets less sunlight due to being farther away from the Sun than Earth).
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2017-09-14, 11:50 AM (ISO 8601)
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Re: Using plants inside a vac-suit to produce oxygen
What Dodom says.
Basically, plants produce oxygen by splitting CO2 and retaining the carbon. So in order to produce oxygen, a plant has to grow. The amount it grows gives you a rough estimate of how much oxygen it produces.
Weight wise there are 32 grams of oxygen and 12 grams of carbon in every 54 grams of CO2. I guess we should also account for the water used, Because every 18 grams of water contains 16 grams of oxygen and only 2 grams of hydrogen.
Now say that half the weight of a plant is just normal water, and the other half is captured carbon and hydrogen from CO2 and water, in the proportion 1:2, as if it is one big polymer chain [CH2]n. That makes the weight proportion 12:2. We're ignoring all the other elements in the mix here. Of every kilogram of mass the plant gains, half is just regular water, about 500/14*12~430g is carbon, and 70 gram is hydrogen. That means the amount of free oxygen produced is 430/12*32+70/2*16~1150+560~1700g of oxygen.
But how much is that, 1700 grams of oxygen? The density of air according to google is a bit over 1.2kg/m^3, which makes sense because with very light gasses you can float around 1kg for every cubic meter of balloon you have. 1.700*1.2=2.040 m^3.
On an average breath you inhale maybe 1.5 liters of air (total lung volume ~ 6 liters), that air is 20-something percent oxygen, but you exchange a lot less than that, say 3%, that means that each breath you take in about 0.045 liters of oxygen or 45*10-6m^3. You take about ten breaths in a minute, for a total of 0.45*10^-3m^3.
So for every kilogram of mass your plant gains you can breathe for 2.040/0.00045~4,500 minutes. This plan works as long as the amount of mass the plants gain every minute is larger than 1/4500=22*10^-3kg=22g.
That's actually not as bad as I thought it would be. I might still be missing some zeroes somewhere. But as is it's not going to fit in a helmet, but with some species of bamboo this might actually be feasible in a decent sized building, as long as you keep shipping full grown bamboo out and water and CO2 in.
EDIT: No wait, I'm an idiot. As Rockphed said, you need to be a panda. You produce the CO2 and water the plants use while you breathe, because duh. The components missing to do that are the carbon and hydrogen in the plants, because that's where you left them. Because also duh. I may be more of a chemist and less of a biologist than I thought, either that or numbers make me go stupid, even if I'm the one bringing them in. And that would make me more of a biologist really.
If we hold out for a slightly larger building we could even use lettuce, or carrots, or anything edible to humans.
Thanks for catching that Rockphed.Last edited by Lvl 2 Expert; 2017-09-14 at 02:22 PM.
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2017-09-14, 02:09 PM (ISO 8601)
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Re: Using plants inside a vac-suit to produce oxygen
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2017-09-14, 02:38 PM (ISO 8601)
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Re: Using plants inside a vac-suit to produce oxygen
We're not *just* worried about O2 production, we're also worried about carbon dioxide reduction. Too high of CO2 levels will kill you dead, even if you have plenty of O2. So yeah, it ends up coming down to growth as an estimate, because that's sequestered carbon.
On earth, there's about 422 trees per person. Granted, there's a lot of other stuff out there besides people, so you can probably cut that down some with a really tailored biosphere. Still, you're unlikely to be able to fit it in a backpack. Perhaps 7 or 8 trees* per person would be about right, but it does vary a great deal depending on type and size of tree.
*Numbers estimated using 12 feet tall, two ton sycamores. Dunno if ideal. Probably not.
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2017-09-14, 03:13 PM (ISO 8601)
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- Apr 2009
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Re: Using plants inside a vac-suit to produce oxygen
Photosynthesis does not make plants grow. It produces sugar (C6H12O6) that the plant saves up during the night to use as an energy source when it grows at night. (Growing directly on sunight doesn't work since it doesn't reach the interior of the plant where growth is taking place. Sugar can be transported throughout the plant when solved in water.)
The main reason why using plants to filter air in space suits is not feasable is indeed sunlight. Without sunlight (and water) a plant can't do anything with the CO2 available. You can get this with lamps, but then you can simply use the energy to power the lamps to power air scrubbers instead. Which are much easier to handle.We are not standing on the shoulders of giants, but on very tall tower of other dwarves.
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2017-09-14, 03:17 PM (ISO 8601)
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Re: Using plants inside a vac-suit to produce oxygen
Going on a slight tangent, what exactly do mushrooms that grow in caves do to obtain energy? Rock walls can't be that nutritious, and sunlight is close to non-existent.
GWLast edited by Grey_Wolf_c; 2017-09-14 at 03:17 PM.
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2017-09-14, 03:42 PM (ISO 8601)
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Re: Using plants inside a vac-suit to produce oxygen
Fungi generally don't photosynthesize anyway. The root-like mycelium is how the organism gathers its nutrients, and the mushroom itself is just the fruit of that vast fungal network. It only lives because there is some kind of nutrition to be found in the rock and soil.
Last edited by Mando Knight; 2017-09-14 at 03:43 PM.
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2017-09-14, 04:14 PM (ISO 8601)
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Re: Using plants inside a vac-suit to produce oxygen
I recall (although I can't track down the exact details now) that they did an experiment once--they created an enormous greenhouse full of plant life, made it air-tight, and sent a group of people in to see how well the plants kept them alive. It didn't actually work all that well, and they had to start pumping in external oxygen because the plants weren't producing enough for the people inside.
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2017-09-14, 04:25 PM (ISO 8601)
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Re: Using plants inside a vac-suit to produce oxygen
Biosphere was the name of the original one. Had a bunch of issues, they made a second one, it also had issues. Looots of issues, including just about everything that can possibly go wrong.
So, it's not something people are really good at yet, but it seems kind of cool as a concept all the same.
Might have honestly just been too small to balance all those different biomes. When you've got only four of a species, you're probably way under the minimal viable breeding population, and individual events quickly throw off the balance.Last edited by Tyndmyr; 2017-09-14 at 04:26 PM.
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2017-09-14, 04:55 PM (ISO 8601)
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Re: Using plants inside a vac-suit to produce oxygen
Actually it was the same biosphere 2 campus used for both tries, neither of which worked out well. "Biosphere 1" was earth.
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2017-09-14, 06:43 PM (ISO 8601)
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Re: Using plants inside a vac-suit to produce oxygen
Its approximately as practical, effective and efficient as Jeremy Clarkson's CO2-Free Land Rover.
The scale would be smaller, but irregardless you'd be wearing something resembling (and probably much larger than - I don't know the plant-to-person ratio either, to be fair) a greenhouse on your head. In space.
Worse, some of the oxygen you breathe in doesn't come back out to be reprocessed by the plants, so no matter how you finagle the system you'll still run out and die.
I haven't the foggiest how oxygen could be processed for breathing in a space suit*; even things like submarines' electrolysis is a fairly hefty device and requires there to be water. There isn't much to use in space to get air out of. Well, there's everything to use in space, but not readily available locally as it were.
*I mean aside from just attaching canisters of the stuff to it.
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2017-09-15, 01:39 AM (ISO 8601)
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Re: Using plants inside a vac-suit to produce oxygen
But the problem was not in the basic idea, rather than in the thousands of details they figured would work themselves out, because that's what seems to happen on full scale earth. The specific frequencies of light let through by the glass produced an abundance of ozon, most of the species inside died out while the ants got everywhere, even taking up the role of flower pollinator (as well as a hairless walking thing can do that) etc etc. It was a disastrously overcomplex setup with several different biomes in one building and everything, and it failed because it turns out we do not know how to do that.
I think since they had some much, much smaller scale experiments with plants on the ISS and stuff, and those actually kind of worked, because those systems were designed to be predictable.Last edited by Lvl 2 Expert; 2017-09-15 at 01:40 AM.
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2017-09-15, 06:42 AM (ISO 8601)
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Re: Using plants inside a vac-suit to produce oxygen
Fungi obtain their energy from plants (more rarely from animals or even other mushrooms) though biodegradation of energy rich materials. When talking about classic mushrooms, the fungi generally fall into one of two categories: those that live in symbiosis with trees and are given nutrients for services such as storing water, and those that directly attack living plants or degrade residual plant matter at the forest floor.
Most commonly, they rely on the energy that is stored in wood. Most of the mushrooms you can buy in a store are grown this way, either on wood chips or other plant material such as coffee grinds.Last edited by aspi; 2017-09-15 at 06:44 AM.
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2017-09-15, 07:58 AM (ISO 8601)
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Re: Using plants inside a vac-suit to produce oxygen
Remembered something about how mushrooms are closer to animals than plants because they don't do photosynthesis but they "eat" other things
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2017-09-15, 08:11 AM (ISO 8601)
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2017-09-15, 11:15 AM (ISO 8601)
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2017-09-15, 11:45 AM (ISO 8601)
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- May 2013
Re: Using plants inside a vac-suit to produce oxygen
I saw something interesting about how evolution dealt with plankton's need to receive light while having as full a calcium armour as they could to avoid being eaten. The solution came in the form of the very first eyeball (which our polyp ancestors likely inherited via horizontal gene transfer, because sometimes, you do gain your enemy's powers by devouring their heart).
The lens allows to take more light in than would happen by just letting what hits that area through, while in its original iteration, the retina was lined with chloroplasts.
Now I could just say that it's possible to concentrate light with lens or mirrors, bring it in via a rather small window, then diffuse it out at the desired surface in the same manner, but I find it way more interesting to bring up that this method not only occured naturally, but was also the eye's first function.
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2017-09-15, 11:52 AM (ISO 8601)
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Re: Using plants inside a vac-suit to produce oxygen
Interested in MitD? Join us in MitD's thread.There is a world of imagination
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2017-09-16, 03:16 PM (ISO 8601)
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Re: Using plants inside a vac-suit to produce oxygen
We are not standing on the shoulders of giants, but on very tall tower of other dwarves.
Spriggan's Den Heroic Fantasy Roleplaying
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2017-09-18, 10:09 AM (ISO 8601)
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2017-09-18, 02:38 PM (ISO 8601)
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Re: Using plants inside a vac-suit to produce oxygen
Mushrooms do gain all their nutrients from dead plants and animals. And since all their energy is provided from chemical reactions from their food and not from light, they are doing well in the dark. Keeping them in the dark means they won't have to deal with moss and algea that can't grow without light. Places with natural light also tend to have decent ventilation because they are open to the sky. With poor ventilation moisture and the warmth from decaying organic matter don't escape as easily, which all fungi like.
Last edited by Yora; 2017-09-18 at 02:41 PM.
We are not standing on the shoulders of giants, but on very tall tower of other dwarves.
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2017-09-28, 08:13 AM (ISO 8601)
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Re: Using plants inside a vac-suit to produce oxygen
More or less, though the "because" is kind of misplaced there as there's no causative relationship there. Fungi are more closely related to animals than to plants. A typical trait that exemplifies it is photosynthesis, which animals and fungi don't have. This is because plants evolved from an ancestor that took on a mitochondria-like and a chloroplast-like microorganism as an endosymbiont, while animals and fungi evolved from something that only took on mitochondria-like microorganisms. The ancestors of fungi split off from the ancestors of animals later.
There's also a lot weirder stuff like protozoans/single-celled eukaryotes, which are complex (unlike single-celled prokaryotes, i.e. everything we think of as bacteria) but not multicellular. Some of them photosynthesise, like dinoflagellates, some of them "hunt" for their food, like paramecia, some do both. Some of them USED to be photosynthetic but turned to a heterotrophic lifestyle later, like the causative agent of malaria. Yeah, that's right - Plasmodium used to be a humble algae-like thing.
And then there's the slime molds.
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2017-09-28, 01:19 PM (ISO 8601)
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Re: Using plants inside a vac-suit to produce oxygen
Yes. Google "slime mold time lapse" for some amazing videos.
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2017-09-28, 02:06 PM (ISO 8601)
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Re: Using plants inside a vac-suit to produce oxygen
Here's an idea: what if instead of in the space suits, we put the plants inside the space station, to refill the air tanks when the astronauts aren't using them?
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2017-09-28, 03:00 PM (ISO 8601)
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Re: Using plants inside a vac-suit to produce oxygen
For a sufficiently large space station with enough greenery, that certainly ought to work, though in practice, constructing such a station might offer some difficulties.
Getting to the point of a decently stable station in orbit that's mostly self sufficient is probably a long ways off, but it'd be a pretty awesome thing to pursue.
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2017-10-01, 12:47 PM (ISO 8601)
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Re: Using plants inside a vac-suit to produce oxygen
Regenerative life support systems that don't require constant replenishing from Earth is definitely something in the agenda, as they'll be imperative for long term expeditions for beyond Earth orbit. Now, on a moon or planet, there can be ISRU*, but in orbit or in transit, you need to recycle.
*in situ resource utilizationLast edited by Ravens_cry; 2017-10-01 at 12:48 PM.
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2017-10-01, 02:52 PM (ISO 8601)
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