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  1. - Top - End - #31
    Titan in the Playground
     
    Brother Oni's Avatar

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    Default Re: How many plants are needed to keep someone alive?

    Quote Originally Posted by Andor13 View Post
    The NASA paper indicates we want 206 g of food per person per day (dehydrated, since we are using dry weight to figure algae production.)
    Can I ask where you get that value of 206g from?

    Page 5 Table 2 says an average male crewman needs 0.62kg food solids a day and 3400 Calories a day. Assuming they're eating pure carbohydrate at 4 Calories per gram that's still 850g worth of pure starch/sucrose, let alone the much less energy dense nori which has 35 Calories per 100grams.

    Quote Originally Posted by Andor13 View Post
    So 21 liters of production volume per person per day would roughly balance out oxygen production, CO2 absorption, and gives you all your bulk food requirements. That's a single 1m by 1m by 2cm panel, per person per day. Considerably more compact that bamboo, and all the nori you can eat.
    Again, I'm not following your math:

    22.0 m2 by 2 cm panel is (220000 cm2 x 2 cm) 440,000 cm3 = 440,000 mL = 440 Litres at a density of 20g dry weight per litre.
    Halve the density, you double the volume, so 880 litres at 10g dry weight per litre. Sticking with 2cm deep panels means you'll also need to double the surface area, so 44.0m2 per person daily.

    The C. vulgaris paper, the maximal rate of cell growth was ~1.5 g dry cell weight per litre per day with a starting biomass concentration of 5 g dry cell weight per litre. Figure 5A seems to indicate rate of growth is broadly independent of the starting concentration, so assume that 1.5 g DCW per litre per day is still applicable at 10 g DCW per litre.

    880 litres would therefore generate an extra 1.32kg dry cell weight of algae a day, which if processed into nori with 100% efficiency, gives you 462 Calories which is about 14% of a male astronaut's needs a day.

    This is assuming you set the flow rate on the panels so that it takes 24 hours for algae to transit across; any faster than that and you'll need to look up more detailed rate of growth and carbon capturing variables. Similarly if you start making the panels thicker, you'll need to look up light penetration into water and the light blocking effects of algae.

  2. - Top - End - #32
    Ettin in the Playground
     
    Griffon

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    Default Re: How many plants are needed to keep someone alive?

    I can't believe it'll be anything other than lettuce that they try first, it's fast growing and moderately edible. Mind you, lack of variety will make any food appalling in a matter of weeks.
    The end of what Son? The story? There is no end. There's just the point where the storytellers stop talking.

  3. - Top - End - #33
    Titan in the Playground
     
    Knaight's Avatar

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    Default Re: How many plants are needed to keep someone alive?

    Quote Originally Posted by Brother Oni View Post
    I'd agree with your proposal that a CSTR with the relevant filters (I can hear the hysterical laughter now) pumping the live algae out into the panels with a CO2 rich water stream (and have regular CO2 feeds in/O2 filters out to maximise speed of yield return), then filtration of O2 before collection back into the CSTR could be viable as a handwaving CO2 recycling / O2 generation system. Just don't approach NASA with the idea unless you want to be laughed at.
    In terms of hiding major engineering problems in plain sight the term "relevant filters" is a thing of beauty.

    Also my proposal is that the panels are the CSTRs, and that instead of the central rotor you use something else to mix them better suited for slow laminar flow. You've got a large, fairly flat panel with a liquid-algae outlet and inlet stream, using nutrient enriched water on inlet, at a slow trickle. Then the panels themselves are mixed as evenly as possible. You also wouldn't need the regular feeds in or out (though an oxygen filter per CSTR would be needed as an outlet stream, given that we're basically building the separator in).

    There's a level of handwaving here, of course, but no more than for the rest of this spaceship.

    *Which does run into a laminar mixing issue, another source of fun. There's a lot of these.
    I would really like to see a game made by Obryn, Kurald Galain, and Knaight from these forums.

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    Current Design Project: Legacy, a game of masters and apprentices for two players and a GM.

  4. - Top - End - #34
    Pixie in the Playground
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    Dec 2021

    Default Re: How many plants are needed to keep someone alive?

    If you have a long-term plan of growing trees to produce oxygen, 1 tree for every 10 people is enough. One mature tree with enough branches and tree can produce enough oxygen in a season for 10 people to breathe clean oxygen for a complete year.

  5. - Top - End - #35
    Titan in the Playground
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    Default Re: How many plants are needed to keep someone alive?

    One mature tree produces zero oxygen, on net. Plants only produce net oxygen while they're still growing.
    Time travels in divers paces with divers persons.
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  6. - Top - End - #36
    Archmage in the Playground Moderator
     
    truemane's Avatar

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    Default Re: How many plants are needed to keep someone alive?

    Metamagic Mod: how many Necroposters are required to keep an expired thread alive?
    (Avatar by Cuthalion, who is great.)

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