Sol 387
MISSION LOG – SOL 387
Tomorrow’s the last hay harvest.
On the one hand I should be happy about that (and even happier that the final potato harvest comes five days later). The rover mods are all finished except for loading the weight in, so we can go straight to field tests. I should be eager to get started. But I’m not.
No matter how sick I am of eating potatoes- and have I mentioned yet that I would like to take a time machine back to the first European explorer who brought potatoes from the New World back to Europe and kill him because there isn’t a prayer of killing the first Inca or Maya or whatever who cultivated the goddamn things? I’m that sick of potatoes, and the ponies are that sick of raw hay, but we invested three hundred and fifty sols, give or take, into the farm- damn near an entire Earth year. That leaves a mark on a person.
Dragonfly says the farm wants to live. That’s fair. So do I. But I don’t know how we’re going to arrange it. We’ve fixed the water issue, and it looks like the heat issue is also covered, but the biggest problem remains: air. The plants require a lot more carbon dioxide than the soil bacteria will ever provide. Without it they’ll suffocate pretty quickly- maybe as slowly as a month, maybe as quick as a couple of days. I’m not sure. It depends on a number of factors.
I’ve thought of a lot of ideas for getting more CO2 into the cave, mostly bad ones.
1) Make hole for Mars atmosphere to enter the cave. This is primo grade-A stupid because (and follow closely here, the details are really technical) if we put a hole in the cave wall, all the air will leave. Take this, write it down on a piece of paper, and underline it: Breach hull, all die. (Well, all the plants. We’ll be long gone. I hope.)
2) Move atmospheric regulator from the Hab to the cave. It’d be nice if that would work, but it can’t. NASA never thought, “Hey, you know what problem our astronauts might have that we’ve overlooked? NOT ENOUGH CARBON DIOXIDE! We better fix that right now!” They’ve never thought it because it’s a dumbass thing. Every aspect of the Hab’s life support is dedicated to extracting CO2 and then ripping it apart in the oxygenator. It can’t be shifted into reverse. And the programming for the atmospheric regulator is on non-programmable ROM chips. So, even if we could power it at the cave, it wouldn’t help.
3) Use MAV fuel plant air compressor to pump CO2 from the outside into the cave. Okay, let’s say we could do this without losing all the air inside. With a bit of thought that’s doable. But here’s the problem: without an atmospheric reclaimer or the ponies’ direct line to their homeworld’s atmosphere, the cave doesn’t have any mechanism to regulate its internal air pressure. The MAV fuel plant would steadily pump compressed outside air into the cave, and the air would stay there, until either the fuel plant died or the overpressurized cave blew out. Breach hull, all die. Not an option.
4) Get Starlight Glimmer to make crystals that exchange molecule for molecule. This is my best idea, but I’m still troubled by it.
Here’s why. Let’s say you enchant a pair of crystals to move air in two directions between them, like the pony space suits and ship life support use. Further refine the spell so that, instead of a free flow of air, the spell detects when a molecule of carbon dioxide hits the outdoor crystal and exhanges it instantly with an oxygen molecule from inside. Simple, right?
Nuh-uh. A molecule of oxygen is two oxygen atoms, total atomic mass roughly 32 atomic units. A molecule of carbon dioxide is two oxygen atoms (dioxide, see?) plus a carbon atom, for a total atomic mass of 44. That’s a net imbalance in the exchange of twelve atomic units- or, put it another way, roughly a third more mass would be entering the cave than leaving. And that’s keeping it simple and not attempting to use the system to squeeze some scarce water vapor out of the air (atomic mass 18).
Now, almost all the carbon atoms will eventually go to making more plants, at a much higher material density than one atmosphere. But more plants take up more space, leaving less space for the existing amount of air. How long will it take before the imbalance causes a problem? And would it even provide enough CO2 fast enough to supply the needs of the plants? I have no idea.
I haven’t floated this one to NASA because they’ve got other things on their minds, namely getting me home and my friends rescued on Sol 551. To them the cave farm is unimportant. It’s only a side issue, one we can do without. When NASA returns, even the dead remains of the farm would have enough data for a generation of future botanists to write page after page about how Mark Watney screwed up or about how there were never any magical aliens, Watney had a psychotic break and made up the whole thing, including the alfalfa.
But it bugs me. It bugs me a lot. We can dump a bunch of water into the cistern before we leave and give the farm enough of a water cycle to last for years. We’ve already given them circulation for water and heating to survive on. But for the cave farm, air is the critical thing, and I wish I had a better solution.
Oh, well. I’ll talk with Starlight about it tomorrow during the harvest and see if she has any better ideas.
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I was wrong! I should have predicted under 1,000 words.
I'm sure those rainbow crystals will have something to do with the solution.
Make an immortal Caterpillar. Something that can eat the plants and turn them into carbon dioxide.
Kinda wondering. He does have a ton of those used CO2 filters he used for his suit. Mayhaps he can use some sort of system to extract the CO2 from those used filters? Like say burning them?
Whatever the solution is, it will probably involve fire.
I still think the solution is just arranging it so some plants live and some plants die. Say, arrange it so only a quarter of the plants get watered. The plants that die will produce carbon for the ones that live. More can be done by leaving any excess harvested plant matter in a pile somewhere in the cave; that too will slowly emit co2 into the cave. Or even just kill everything in the cave except the cherry trees; that would leave enough carbon for the trees to survive for a long long time.
The carbon already in the cave will stay there (unless it leaks, but if it leaks they have bigger problems than the co2 levels, as Watney notes in this chapter). If the cave currently has two thousand pounds of living plants, it can continue to support two thousand pounds of living plants more or less indefinitely; it's only if they end up with three thousand pounds that things get problematic. And as the carbon level goes down, the plants will grow slower, thus being some level of self regulating.
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9075643
The problem with that is he can add any amount of co2 they want to before they leave, by concentrating it from Mars' atmosphere. What he's looking for is more a way to continue introducing co2 after they're gone.
Soooo... Wouldn't Mark know that plants actually conduct photosynthesis in reverse? I'm not joking here, this is an actual thing. In seventh grade, we did an experiment on how a plant could survive underwater with little light. After a week, when we took out the plant from the closet, there were small air bubbles gathered on the leaves, as well as the plant having grown a few inches in the test tube. The reason why plants developed like that is because even in forests with a high animal population density, the amount of oxygen trees and other plants would produce would easily outweigh the amount of carbon dioxide the animals would put back into the atmosphere. A great enough imbalance that the plants would slowly lose their source of food in the form of carbon dioxide. That's why evolution decided to say, "Fuck it, you make too much air. So, here's a way to reverse that and make air you can eat out of the air you shit out. Now don't die."
What the farm needs is an artificial form of respiration, and preferably one that doesn't involve fire. Although... a controlled burn of methane might end up being the only solution available to the Mars crew. And I DO want to put emphasis on the word "controlled" in that sentence; think the kind of controlled burn you get from a propane stove, for concept.
There are exactly 2 problems I can think of with this, though: first off, they'd need to cultivate more of the bacteria that were involved in the Cave Fart, and I don't think they'd exactly be willing to do that. Second, and arguably the bigger of the two problems, they'd need a way to contain the methane that's being produced until it's ready to be burned... that might not be possible, given the distinct lack of materials on hand
9075691
It would also run into the same problem as his crystal transfer idea - it would gradually increase the pressure in the cave until it burst.
Personally I'm hoping they completely mess up the cave farm project and accidentally terraform Mars.
It's a bad idea, but he could deliberately induce controlled periodic "forest fires" that burned specific sections of the farm in rotation. The combustion would consume the oxygen and replace it with carbon dioxide, it's the most primitive form of res so to speak. It would also have the benefit of being a method of population control so the plants didn't crowd themselves out
9075747
Mars: The blue spots.
PPS agent: But, you're entirely blue?
Mars: well, I was entirely red before.
PPS agent: Oh.... OHH!
Light a very small candle?
I've calculated some time ago that the cave took ~10000m3 of water without even noticing, so it's volume probably starts at 107 m3. That's 6 tons of CO2 (at 300ppm). From the size of their harvest, plants use no more that 100kg of carbon per month (or 350kg of CO2), so definitely not days
Can Starlight magic something that passes CO2 through, but not other gases? Then partial pressures of CO2 inside and outside would equalize, and it would be ~6000ppm inside --- plants definitely wouldn't be very happy about that, but they'll survive (strictly speaking, they wouldn't precisely equalize and concentration would be less depending on temperature difference, air properties and magical kinetic properties). With additional calculations It could probably be improved by using small enough hole or something. There's still problem with oxygen building up inside (as with many other options), but, from above, it would take at least a few years to raise pressure 1%. Also they are very likely to have 1bar pressure regulator somewhere, so they may just stick it in.
9075792
Australia on Mars?
Problem with that would be extra heat.
Magic solution wouldn't cause overpressure that quickly, because of phase change between solid and gas is so different in volume. But I suspect that there is thermodynamic issue. We replace one molecule with another, one that would have different energy and degree of freedom. What would happen to temperature in cave?
Those lazy plants need to start pitching in every now and than.
The trouble with the wet sump, digester, methane, platinum catalyst burner model, primarily, is getting the plant matter into the digester, or swamp. Effectively, to get the atmosphere as part of the cycle, without movement eing an option, would be to have the Cave Farm enter the Carboniferous, using a low level CO2 pump in?
The atmospheric regulator should have a CO2 regulation circuit as too high has effects, but too low and your breathing reflex doesnt trigger or something? Might have been story handwavium from years ago but these things do like to spring out and suprise you.
At least for first charge he can use lightly insulated buckets at night and carry CO2 into the place? I suspect even the very far end is far too warm and they cant afford to build Goop tanks capable of handling the pressure?
So what you do instead is create a crystal-powered pressure sensor.
If pressure is below a level, let co2 in, if high, let o2 in. If balanced, let both flow.
With this, there would be no need for a molecule for molecule system, just let the crystals continually run when allowed by the sensor.
Uh, sorry to be the bearer of bad news but... let's just say this chapter was not written by a botanist.
First things first. Plants do need carbon from CO2 but only to build their mass. Once they do that, they go carbon-neutral. So when we say that plants produce oxygen, we're perpetuating a slight misconception. Growing plants do. For the cave it would be a problem if someone continued the harvests, taking away large portions of carbon and never bringing it back. It does happen naturally, but it happens over the course of eons. Coal, peat, topsoil, and various sedimentary formations are examples of carbon removed. It's not a problem for the cave.
Second, Mark can create a safety buffer if he so desires. All those plants in The Hab are destined to die. Harvest them and transport to the cave. The soil too, if possible. Compost them. And then the cave itself is enormous. It is thousands and thousands of cubic meters in just the habitable part. Also, a quick search says that CO2 is not really toxic to humans in concentrations under 5% (per NIH). That's huge. If Mark is that paranoid about CO2, he can infuse the cave air with just 0.1% carbon dioxide (roughly twice the current Earth levels). Moreso only the top part of the cave is inhabited. The CO2 would concentrate in the lower rooms. Perhaps CO2 levels there could become toxic (to humans, I'm sure plants could endure more), but who cares, those parts are lifeless anyways. Over the years CO2 would diffuse slowly upwards when needed (or make a magic ventilation system, but really that is not needed).
TL;DR: not a problem, Mark is having a huge derp that would disqualify him as a botanist. His Mars Bottle Garden is big enough to thrive for decades and decades.
9075492
Well, someone mentioned that Starlight accidentally Terra formed Mars. Just thought I'd show it is very well in the realm of possibility.
9075658
Yep, plant can do reverse photosynthesis, as well as animals, it is called breathing, and burning sugar and oxygen into water and carbon dioxide.
Plants breath just like animals, they also do photosynthesis during daylight, but breathing never stops for them too.
9076005
I was about to post the same solution. Just empty out those co2 bottles in the back of the cave when they leave, but before they remove the life support box (#name) so that pressures might equalize. Or don't, more air = not a problem.
And I was going to point at bottle gardens for reference. Co2 influx is not key to plant survival.
Also, I don't get why keeping molecular weight not being the same with the enchantment matters at all.
I would Ares 4 to go back to that cave. Alien alfalfa, alien cherry's? That is way more interesting then those martian rocks. The remains of an alien spaceship, including magical technology that could solve our energy problems (magic = untapped resource that can be converted to electricity. Can it power the grid? Can it power cars? Can it power Hermes if its reactor breaks down? Without creating heat? Maintenance is still overdue. NASA should be concerned)
Wireless power transfer using solar collector crystals would be awesome if they could power phones. They proved capable of transferring electricity.
But if it's Mars rocks is what you crave after, fear not, there is a cave full of the more interesting specimens.
If Elon Musk is still around, this would probably prompt him to start a colony if earth and pony's let him. If he gets his hands on that life support box, and a unicorn to seal caves, let the terraforming begin.
Don't plants have a respiration cycle like animals do? CO2 consumption during the day while photosynthesis is occuring, O2 consumption at night to restore ATP reserves, if I remember my high school biology classes correctly. Mainly plants construct themselves by pulling carbon out of the air for their biological structure, the O2/CO2 is there to help the process along. Therefore the cave should be fine as it is, kind of like those bottle gardens that can live for decades in a closed environment.
Besides, if all else fails Starlight could always just create a small charmed flame to burn for as long as there's magic to draw from in the farm. That way it'd be burning at a slow, controlled rate while exchanging O2/CO2. The problem there is that (most) normal fire is burning a carbon based fuel source, hence the C in CO2. But then again... magic. BEHOLD, A PLOT DEVICE NEUTRALIZER!
I dunno, just a few thoughts.
Is what went through the mind of whomever designed the mav refueling system. It can remove CO2 from mars atmosphere and bottle it.
9076060
Yeah, I did not understand why the (molecular) mass disparity is a problem. As the plants grow they compact carbon into more dense forms. Cherries growing trunks and branches would be prime consumers of carbon. Okay, so the whole point of the system would be to maintain the air pressure while increasing total carbon mass in the cave. That's like the whole point: to bring more carbon while maintaining parity of other elements (not like that is needed in the first place, but supposing it is, the molecule-for-molecule exchanger is the ideal solution).
9075658 9076005 9076060 The key points in your objections:
(1) "Don't plants breathe normally too?" - Yes, and I pointed that out much earlier in the story. But it's not a perfect balance, and the bias is towards pulling carbon out of the air.
(2) "But it's only imbalanced while they're growing!" - Yes, and Mark expects a lot of growth after they're gone. Not all plants are suitable for a bottle garden. The alfalfa might- MIGHT- stop growing after a while, above the surface, though the root system will go as deep as possible. But despite accelerated growth the cherry trees will be growing for a long time, and the potatoes will bud out from their tubers and spread across the cave floor almost indefinitely.
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That's the thing, though. If they have no carbon, they would stop growing, but not die. I grow bonsai as a hobby. My plants take a lot of abuse from me, and sure, by natural standards, they are puny dwarfs. Even their leaves are unnaturally small (which is very desirable). But they don't die.
But okay, disregard this and disregard the cave size as a great buffer that could last decades and decades.
Why is the molecule exchanger a problem then? It brings in more carbon, keeping the oxygen mass a constant. That is good, then.
9076213 Mark is unsure of how the imbalance long-term will affect air pressure in the cave. He doesn't want to leave a bomb behind, even if the timer is measured in years.
Simple solution would be day/night cycle. During night plants create CO2 and don't grow so much.
9076225
Errr, what? There is an upper theoretical limit to how much the pressure can rise if we magically exchange all the oxygen for CO2. The Earth air has 20% oxygen (so Equestrian air too, I presume?) Which means that exchanger could potentially increase the total gas mass (therefore: pressure) in the cave by... (napkin math) 7.5%. Is that too much? And that would happen if the exchanger swapped literally metric tons of oxygen for CO2. Well, throttle it down? Slightly depressurize the cave beforehand?
9076251
This is false. Those plants will take that co2 and Transform it automatically into plant mass and O2 which can then be exchanged again. The cave gains 1 carbon atom.
Considering this carbon stays in solid or liquid form, it might not add anything measurable to the air pressure, but eventually... In a few 100 years or so.
Personally I'd be more worried about liquid water.
But, they have a few bigger problems, in no particular order, yet to solve.
Fireballs lack of gold in his diet. He can't keep that up forever. It's been about a year now.
Dragonfly magic-starved on the trip to Earth.
Mars
Dragonfly staying in the cave might fix 2 problems, but I still don't like it.
9076199
Imho, the main point we were making is:
Cave big, lots and lots of co2 already in cave, can add more before leaving. Can even fill other cave with co2 (MAV co2 plant) and connect them caves when they leave. Crazy overkill but with magic, doable.
Someone will come and study cave before it's dead. Twilight Sparkle will want to see that self-replicating chaotic magic.
Humans will want to see the exobiology.
9076341
actually given that the sparkle drive would essentially get them back to earth in about a week from what I remember dragonfly could hold on that long... she's still filled with determination plus my theory is that earth would have made a torus of magic in the path of its orbit given it is so jam packed with life and as the ponies said more life=more magic they might start charging the batteries and feeling magic around lunar orbit... given how much life is on earth the planet would have an ambient magic field
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9076341
Well, yes, the cave gains mass. But the plants store it as sugars and cellulose, and it would take thousands of years to fill the cave with dead plant matter to the point it will raise the pressure noticeably. We are talking about hundreds of cubic meters of topsoil, peat, and lumber. The cave would run out of other chemical elements before the pressure becomes a problem.
9076349
1) It has not been proven that earth life generates a life field. (Unless I missed something)
2) I would not bet someone's life on the sparkle drive working.
3) There is the travel across Mars surface where magic is a limited resource. No getting around that. They might consume to much magic to even attempt a sparkle drive.
9076360
eh... the potatoes(of earth origin) helped generate magic alongside the alfalfa of equestrian origin... I would assume a planet bursting at the seams with life like earth is would have a POWERFUL ambient magic field I mean there isn't a square millimeter of earth that DOESNT have life on it...
also I bet they could get to the ares 4 site if they hustle as fast as possible and make sure all the batteries are at 100% of course equestrian tech might fail so does human tech
9076225
What's the maximum volume of plant Mark can imagine the cave supporting, as compared to the volume of the cave? I'd expect that to be a pretty small ratio, and thus a small increase in pressure. Running out of carbon isn't the only thing that will provide an upper bound on growth. But I'm no exobotanist and don't have the cave volume at my fingertips either.
(Also, of course, the straightforward solution to an overpressure problem would be a pressure relief valve. Not very complicated to do mechanically, but probably not something they have the metal-working to fabricate and might fail when unattended on Mars for years. A magic one might be relatively simple though - they just need a life-support crystal pair that activates if and only if the inside pressure is too high.)
It seems that the Maxwell's Demon De-oxygenator would pose a different problem if the farm reached a 'no net growth' equilibrium, bleeding away the oxygen needed for aerobic decomposition of dead plants and eventually making the cave dangerously anaerobic.
9076251
The exchange rate is one molecule for one molecule --- it doesn't change pressure (with practically relevant precision).
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9076479
To expand on what mishun’s saying, a molecule of gas at a given temperature exerts a certain pressure, essentially regardless of how big it is. The change in pressure of a single degree Fahrenheit would constitute a greater change in pressure than instantly swapping out all the oxygen for CO2.
Now I don’t expect Mark and all his powers of botany to know this, but the moment he floats the idea to all those rocket scientists for whom gas pressure is a very big thing, someone would point that out to him.
And solids are so much more compact than atmospheric gas that we’re talking centuries before it could cause a blowout, long after even the most optimistic would expect the airlock to fail on its own.
Just leave Sojourner to tend to the farm. :D
9075733
If they do, it'll be from the inside-out, turning most of it into a massive version of Journey To The Center Of The Earth... minus any
slo-mo giant lizardsscary dinosaurs.9076785
His engineer hat should cover gas law. Especially give his employment.
"Ah, here it is: Breach Hull - All Die, even had it underlined!"
9076479 It's the old PV = nRT ideal gas law equation.
Or, pressure x volume is directly proportional to temperature times a rate constant and the moles of gas.
As one can see, the size of the gas molecules indeed does not affect the properties of gasses at relatively low pressures and numbers of molecules for the simple fact that the space between the molecules at these low pressures is vastly larger than the average molecular radius. Indeed, the cave blowout would occur at pressures far below the point where molecular size would significantly affect the values of the general gas equations.
Intermolecular attractions are also of limited importance at typical atmospheric pressures and terrestrial atmospheric composition.
Mark, Mark, did you forget the 19th century or so invention of a relief valve? Pressure rises over a given threshold, the valve opens and releases the excess. It's a pretty simple engineering, just have a good spring hold a cover over a hole, too much push, the spring gives, hole opens, air escapes. Pressure drops, cover is pushed back. Add a screw to regulate how hard the spring pushes, there, done.
Saw that #1 coming, yes
What does the Oxygenator actually do with the CO2 it filters out? Can they... collect that, somehow?
10102062 The oxygenator strips the oxygen off the CO2 molecules and disposes of the carbon, leaving pure oxygen.
10102482
Ah, right. It's processed, not dumped...
Broken format.
Basicly the Farm is dead no matter what.
Neat chapter ones the format is edited.
Edit:
I was apperently wrong ¯\_(ツ)_/¯