shiplog #0011 t+2120-11-15t016:12:42.105755 I’m…in trouble. Again. This stupid shuttle’s stupid life support system can’t keep up. The original crew must have ‘salvaged’ a significant chunk of the scrubbers for ‘parts’ (I think they sold them). I guess they only expected this thing to be on it’s own air for a few months at a time max. I probably have another 2-3 months before the CO2 concentration is too high and I’m SOL. Evaluating my options here:
- If I can get my hands on enough water, I can setup a sebatier reaction - problem is, I don’t have the necessary tools for that, although if I ever want to make propellant I’ll need to do it someday
- I can try to get some of these seeds going - this would be a good long term solution, I’ll especially need it for food, but I don’t think they’ll grow fast enough to sequester the CO2 in a standard growth medium.
- I can vent the shuttle - I hate this idea, but if I vent the shuttle I can use the fresh reserve air, but I think that will put me back where I started.
I need some time to think…
shiplog #0012 t+2120-11-16t022:01:00.127849 I think I’ve got it. Hydroponics. Growing plants in soil is great, but they don’t grow fast enough and I’d need a fairly large space to grow enough plants to keep me going. Not to mention the amount of water it would take…
Hydroponics, on the other hand, is a different approach. It’s essentially the growing of plants without soil. In my case, a nutrient rich liquid bath that I run over the roots of the plants. Using this approach can increase crop yields by 3 times or more, reduce water consumption by up to 90%, and increase growth rate by 30%-50%. Not bad!
How much is enough?
So my main problem isn’t necessarily producing oxygen, but getting rid of CO2. Not to mention food, but air is the immediate problem. To figure out how many plants I need I’m going to do some basic first order approximations and make some big assumptions. Namely, the majority of a plants carbon comes from the CO2 it absorbs from the air. Now, a typical human produces 500 liters of CO2 a day which constitutes about 1 kg of CO2. It’s important to note the carbon comes from the things we eat and the oxygen from the air we breath. So at the minimum I need enough plants to balance my production as I’m going to eat them and convert their carbon back into CO2.
First thing to figure out is how much carbon is in a kilogram of CO2. The atomic weight of carbon is 12 and the atomic weight of oxgen is 16 for a grand total of 44 atomic mass units for CO2. Carbon accounts for then 12/44ths of that mass. So my 1kg of CO2 is (12/44) * 1kg = .272kg of carbon. I need to grow .272grams of food-carbon by weight. So how much of a plants mass is carbon? (I don’t know actually and I can’t find a good source so I’m going to assume 30% carbon by weight for bean plants). If a bean plant is 30% carbon by weight, then we need .272/0.3 = 0.9kg of beans grown per day at least. In a hydroponics system, I can bring a bean plant to maturity in 60 days and the yield per acre for beans is ~21 tons/acre or 4.71 kg/m^2. This means ~.078kg/m^2/day yield. Ok! So to reach my 0.9kg/day target I need 11m^2 of growing space… oof, that’s not small and my hab sure is. (Compare this to ~44m^2 of space I’d need if I was growing in soil).
Here comes vertical hydroponics to the rescue! With hydroponics it’s actually possible to grow plants in a tower like system saving a lot of space.
Vertical hydroponics system
Ok so I need to build a vertical hydrponics system. I’m going to build it 2.5 meters tall and I’ll need at least 5 units each which takes 1 m^2. I can use some of these standard pipe units I have to contain the plants and to run the water over the roots. I’ll pump the water to the top of the tower and let it run down to the bottom.
 https://www.saferbrand.com/articles/hydroponic-growth-rate  https://www.sciencefocus.com/planet-earth/how-much-does-human-breathing-contribute-to-climate-change/  https://scienceinhydroponics.com/2020/06/average-yields-per-acre-of-hydroponic-crops.htmOl