7 ms·

From the article: > You might be familiar with this if you know about electrolysis. On Earth this process is commonly used in manufacturing, such as to produce

From the article: > You might be familiar with this if you know about electrolysis. On Earth this process is commonly used in manufacturing, such as to produce aluminium. An electrical current is passed through a liquid form of aluminium oxide (commonly called alumina) via electrodes, to separate the aluminium from the oxygen. In this case, the oxygen is produced as a byproduct. This is currently not the industrial reality. Aluminum is typically produced via the Hall–Héroult process which involves a carbon source and emits CO2. (Alternative processes which only emit oxygen are possible, but presumably those are more expensive.) https://en.wikipedia.org/wiki/Hall%E2%80%93H%C3%A9roult_process https://en.wikipedia.org/wiki/Hall%E2%80%93H%C3%A9roult_proc...

TheOtherHobbes 5y ago
One of the first and most immediate challenges for any Moon or Mars base is an excess of CO2. It won't cause lunar warming. But it will still be a problem and require significant energy and other resources. It's likely that it will either be impossible or prohibitively expensive to keep CO2 levels at normal Earth standards. See also: the ISS which operates with much higher atmospheric CO2 levels (up to 5000ppm) than would be considered healthy on earth (up to 1000ppm).
- navaati 5y ago
  Wow, I pity the poor astronauts that have to do science inna state of dizziness !
- xyzzy_plugh 5y ago
  Interesting, I didn't know this about ISS. I've fought a tiring battle to get my CO2 levels below 500ppm consistently, and it's night and day compared to the 800-1200ppm I used to measure. Can't even imagine what 5000ppm is like!
  - nolroz 5y ago
    Have you felt benefits from getting your levels lower? What steps did you take? Do you have a sensor you recommend?
    - tailspin2019 5y ago
      Also interested in the answer to this!
    - dbsmith83 5y ago
      You can just open a window and circulate air in the home to lower CO2 levels. I use a uHoo sensor https://getuhoo.com/ https://getuhoo.com/
      - vkat 5y ago
        How has the uHoo sensor worked for you?
        dbsmith83 5y ago
        So, I bought one and it was great, but then randomly the CO2 sensor seemed to stop working after a few weeks. It stayed at the exact same ppm level without changing for a while. I sent an email to customer support and they shipped me a new one for free, and didn't even require me to send back the old one. Haven't had any issues since. I'm pretty happy with it.
    - sparker72678 5y ago
      Not the OP, but I've been using a model by Awair for a while now (looks like they've released a new product that's a bit more expensive since I got mine). I work in a very small office shed, and if I leave the door and window closed tight it will quickly get over 2000 ppm (45-60 min). At that point I'm typically feeling more tired, and a bit foggy. By keeping the window cracked I can keep the readings down in the 800-1100 range, and I feel much better.
      - Aspos 5y ago
  - CoastalCoder 5y ago
    I remember discussing this a while back on HN, and one issue was that consumer-grade CO2 meters aren't reliably calibated. So just curious for my own designs, how certain are you about those ppm numbers you listed?
    - OJFord 5y ago
      Not GP (nor a metrologist) but 50% reduction is surely the important thing anyway, in a home setting, not the absolute figures? I don't think the curve could be much off, since they work by counting particles, so if it's reading high at 800ppm then it should be reading just as high at 500ppm right?
      - CoastalCoder 5y ago
        I agree that presumably less CO2 is better than more. I'm thinking that the specific CO2 concentrations matter if one wants to relate the readings to various research on human mental performance.
    - eightysixfour 5y ago
      I have tested quite a few against calibrated commercial hardware at this point and they’re not as poorly calibrated for CO2 as you would think. The particulate counts and VOCs are usually only good for comparative measurements from the same device in my experience, and even then the drift is quite large.
      - JohnJamesRambo 5y ago
        All my CO2 meters read about the same as the one in my grow room that controls the CO2. I don’t think that is a big problem.
      - mdp2021 5y ago
        I am desperately looking for one for the car, do you have anything to suggest? Also, I am finding products that seem to require an Android or iOS device to work: no. They must be independent. If they had a webserver, nice idea, but all connections should be unrequired and switchable to off.
  - Raz2 5y ago
    My CO2 sensor self calibrates to show 400ppm as outdoor / minimal concentration. I was very upset to find out that it's not correct. In the last 5 years outdoor concentration rose from ~400 to ~420. Guess my kids won't be able to maintain < 500ppm.
- ajuc 5y ago
  > It's likely that it will either be impossible or prohibitively expensive to keep CO2 levels at normal Earth standards. I think we shouldn't use orbital space station where space and energy is very constrained as model for lunar base (where space and energy will be quite easy to get by comparatively). Average person breaths out ~1kg of CO2 per day or ~400 per year [1]. Corn field absorbs ~4000 kg of CO2 yearly per 1000 m2 [2]. The same 1000 m2 field will produce ~4000 ears or 320 000 kcal yearly [3][4] Assuming 2000 kcal for average person (so 730 000 kcal yearly) - we need 2000 m2 of corn fields to produce food for that person and just 100m2 to absorb CO2 from that person. Food will be a more important constraint in a self-sustaining base. That means if we build lunar base in the lava tubes (that are often over 300 meters wide and go on for kilometers), we can keep them self-sustainable at density of 1 person per less than 10 meters of the lava tube. [1] https://www.nrdc.org/onearth/waiting-exhale#:~:text=So%20breathe%20easy.,CO2%20as%20his%20sedentary%20brethren https://www.nrdc.org/onearth/waiting-exhale#:~:text=So%20bre....) [2] https://www.canr.msu.edu/news/corn_fields_help_clean_up_and_protect_the_environment https://www.canr.msu.edu/news/corn_fields_help_clean_up_and_... [3] https://www.quora.com/How-many-ears-of-sweet-corn-are-in-an-acre https://www.quora.com/How-many-ears-of-sweet-corn-are-in-an-... [4] https://www.nutritionix.com/i/usda/corn-1-ear-medium-6-0.75-to-7-1-2-long-yields/513fceb575b8dbbc21001520 https://www.nutritionix.com/i/usda/corn-1-ear-medium-6-0.75-...
  - lazide 5y ago
    That math seems a bit implausible if you look at it from a closed system perspective. For said 1000m^2 field, it has to get the carbon from somewhere to produce the food, that then powers 6 months worth of activity for said human. If a human via respiration can only provide a tiny fraction of it (per the inverse of the other statement regarding:amount of Co2 absorbed for the field), where does the rest come from? Decaying organic material? Soil? Both of those are problematic closed system wise. There is a lot of very dubious math in everything from ‘amount of water consumed’ and ‘amount of carbon absorbed’, etc. which if you dig into it really doesn’t add up. This feels like one of them?
    - jjk166 5y ago
      You would have to bring in enough carbon for the initial setup. Once you have enough material to grow the first crop, you will decompose previous crops to provide carbon and other nutrients for subsequent crops. In a closed system, none of that is being destroyed. In a real system you will get some losses (absorbtion by structural materials, population growth, leaks, etc) but these would be small compared to the overall amount, and easily made up with resupply at first and mined material over the long term.
- Robotbeat 5y ago
  It’s take much less energy to maintain Earthlike CO2 levels in a habitat than it already does to make the oxygen that astronauts consume.
- neartheplain 5y ago
  The Soviets solved this problem in their closed ecosystem experiments of the 1970s using 8 m^2 of algae per person: https://en.wikipedia.org/wiki/BIOS-3 https://en.wikipedia.org/wiki/BIOS-3
- coryfklein 5y ago
  Forgive my ignorance, but why is excess CO2 such a challenge? Isn't it extremely easy to simply vent it into space/the nearly-empty moon atmosphere?
  - jjk166 5y ago
    Carbon isn't plentiful on the moon's surface so you want to conserve it for long duration missions/permanent habitats. Unfortunately storing it as CO2 in the air isn't great for human health.
    - ajuc 5y ago
      You need food production anyway for a sustainable moon base. After the harvest store waste plant matter and burn it over the next season to keep the CO2 concentration in air good for plants and for you. It's a closed cycle if you eat/burn everything you grew each growing season, and you can keep the air CO2 concentration stable by adjusting how much waste matter you burn vs how much CO2 is captured by the plants. You need about 2000 m2 of corn to feed one person over 1 year and just 100 m2 of corn will capture the CO2 exhaled by that 1 person in 1 year. Assume we live in horizontal lava tubes 300m wide, let's say 10 meters of that tube per person to have some margin of error. That's <535 kg of CO2 in air in that section of the tube and ~8000 kg of CO2 captured in corn planted there the moment before harvest. It's doable IMHO. At least napkin math checks out.
      - loonster 5y ago
        Corn is a great plant optimized for production per acre. On the moon it may be more beneficial to optimize for carbon stability. Get plants with a more favorable Edible Carbon::Total Carbon ratio. A plant that can be harvested continuously would also be beneficial. The ideal plant may be something simple like grass. We can't eat it, so would need another intermediate step. Possibly Cows or Sheep. These would be grown for milk and not meat.
        klondike_klive 5y ago
- Jarwain 5y ago
  if we figure out efficient methods for carbon capture planetside, couldn't we reuse those methods for any non-terrestial habitat?

TheOtherHobbes 5y ago

One of the first and most immediate challenges for any Moon or Mars base is an excess of CO2. It won't cause lunar warming. But it will still be a problem and require significant energy and other resources. It's likely that it will either be impossible or prohibitively expensive to keep CO2 levels at normal Earth standards. See also: the ISS which operates with much higher atmospheric CO2 levels (up to 5000ppm) than would be considered healthy on earth (up to 1000ppm).

navaati 5y ago
Wow, I pity the poor astronauts that have to do science inna state of dizziness !
xyzzy_plugh 5y ago
Interesting, I didn't know this about ISS. I've fought a tiring battle to get my CO2 levels below 500ppm consistently, and it's night and day compared to the 800-1200ppm I used to measure. Can't even imagine what 5000ppm is like!
- nolroz 5y ago
  Have you felt benefits from getting your levels lower? What steps did you take? Do you have a sensor you recommend?
  - tailspin2019 5y ago
    Also interested in the answer to this!
  - dbsmith83 5y ago
    You can just open a window and circulate air in the home to lower CO2 levels. I use a uHoo sensor https://getuhoo.com/ https://getuhoo.com/
    - vkat 5y ago
      How has the uHoo sensor worked for you?
      - dbsmith83 5y ago
        So, I bought one and it was great, but then randomly the CO2 sensor seemed to stop working after a few weeks. It stayed at the exact same ppm level without changing for a while. I sent an email to customer support and they shipped me a new one for free, and didn't even require me to send back the old one. Haven't had any issues since. I'm pretty happy with it.
  - sparker72678 5y ago
    Not the OP, but I've been using a model by Awair for a while now (looks like they've released a new product that's a bit more expensive since I got mine). I work in a very small office shed, and if I leave the door and window closed tight it will quickly get over 2000 ppm (45-60 min). At that point I'm typically feeling more tired, and a bit foggy. By keeping the window cracked I can keep the readings down in the 800-1100 range, and I feel much better.
    - Aspos 5y ago
- CoastalCoder 5y ago
  I remember discussing this a while back on HN, and one issue was that consumer-grade CO2 meters aren't reliably calibated. So just curious for my own designs, how certain are you about those ppm numbers you listed?
  - OJFord 5y ago
    Not GP (nor a metrologist) but 50% reduction is surely the important thing anyway, in a home setting, not the absolute figures? I don't think the curve could be much off, since they work by counting particles, so if it's reading high at 800ppm then it should be reading just as high at 500ppm right?
    - CoastalCoder 5y ago
      I agree that presumably less CO2 is better than more. I'm thinking that the specific CO2 concentrations matter if one wants to relate the readings to various research on human mental performance.
  - eightysixfour 5y ago
    I have tested quite a few against calibrated commercial hardware at this point and they’re not as poorly calibrated for CO2 as you would think. The particulate counts and VOCs are usually only good for comparative measurements from the same device in my experience, and even then the drift is quite large.
    - JohnJamesRambo 5y ago
      All my CO2 meters read about the same as the one in my grow room that controls the CO2. I don’t think that is a big problem.
    - mdp2021 5y ago
      I am desperately looking for one for the car, do you have anything to suggest? Also, I am finding products that seem to require an Android or iOS device to work: no. They must be independent. If they had a webserver, nice idea, but all connections should be unrequired and switchable to off.
- Raz2 5y ago
  My CO2 sensor self calibrates to show 400ppm as outdoor / minimal concentration. I was very upset to find out that it's not correct. In the last 5 years outdoor concentration rose from ~400 to ~420. Guess my kids won't be able to maintain < 500ppm.
ajuc 5y ago
> It's likely that it will either be impossible or prohibitively expensive to keep CO2 levels at normal Earth standards. I think we shouldn't use orbital space station where space and energy is very constrained as model for lunar base (where space and energy will be quite easy to get by comparatively). Average person breaths out ~1kg of CO2 per day or ~400 per year [1]. Corn field absorbs ~4000 kg of CO2 yearly per 1000 m2 [2]. The same 1000 m2 field will produce ~4000 ears or 320 000 kcal yearly [3][4] Assuming 2000 kcal for average person (so 730 000 kcal yearly) - we need 2000 m2 of corn fields to produce food for that person and just 100m2 to absorb CO2 from that person. Food will be a more important constraint in a self-sustaining base. That means if we build lunar base in the lava tubes (that are often over 300 meters wide and go on for kilometers), we can keep them self-sustainable at density of 1 person per less than 10 meters of the lava tube. [1] https://www.nrdc.org/onearth/waiting-exhale#:~:text=So%20breathe%20easy.,CO2%20as%20his%20sedentary%20brethren https://www.nrdc.org/onearth/waiting-exhale#:~:text=So%20bre....) [2] https://www.canr.msu.edu/news/corn_fields_help_clean_up_and_protect_the_environment https://www.canr.msu.edu/news/corn_fields_help_clean_up_and_... [3] https://www.quora.com/How-many-ears-of-sweet-corn-are-in-an-acre https://www.quora.com/How-many-ears-of-sweet-corn-are-in-an-... [4] https://www.nutritionix.com/i/usda/corn-1-ear-medium-6-0.75-to-7-1-2-long-yields/513fceb575b8dbbc21001520 https://www.nutritionix.com/i/usda/corn-1-ear-medium-6-0.75-...
- lazide 5y ago
  That math seems a bit implausible if you look at it from a closed system perspective. For said 1000m^2 field, it has to get the carbon from somewhere to produce the food, that then powers 6 months worth of activity for said human. If a human via respiration can only provide a tiny fraction of it (per the inverse of the other statement regarding:amount of Co2 absorbed for the field), where does the rest come from? Decaying organic material? Soil? Both of those are problematic closed system wise. There is a lot of very dubious math in everything from ‘amount of water consumed’ and ‘amount of carbon absorbed’, etc. which if you dig into it really doesn’t add up. This feels like one of them?
  - jjk166 5y ago
    You would have to bring in enough carbon for the initial setup. Once you have enough material to grow the first crop, you will decompose previous crops to provide carbon and other nutrients for subsequent crops. In a closed system, none of that is being destroyed. In a real system you will get some losses (absorbtion by structural materials, population growth, leaks, etc) but these would be small compared to the overall amount, and easily made up with resupply at first and mined material over the long term.
Robotbeat 5y ago
It’s take much less energy to maintain Earthlike CO2 levels in a habitat than it already does to make the oxygen that astronauts consume.
neartheplain 5y ago
The Soviets solved this problem in their closed ecosystem experiments of the 1970s using 8 m^2 of algae per person: https://en.wikipedia.org/wiki/BIOS-3 https://en.wikipedia.org/wiki/BIOS-3
coryfklein 5y ago
Forgive my ignorance, but why is excess CO2 such a challenge? Isn't it extremely easy to simply vent it into space/the nearly-empty moon atmosphere?
- jjk166 5y ago
  Carbon isn't plentiful on the moon's surface so you want to conserve it for long duration missions/permanent habitats. Unfortunately storing it as CO2 in the air isn't great for human health.
  - ajuc 5y ago
    You need food production anyway for a sustainable moon base. After the harvest store waste plant matter and burn it over the next season to keep the CO2 concentration in air good for plants and for you. It's a closed cycle if you eat/burn everything you grew each growing season, and you can keep the air CO2 concentration stable by adjusting how much waste matter you burn vs how much CO2 is captured by the plants. You need about 2000 m2 of corn to feed one person over 1 year and just 100 m2 of corn will capture the CO2 exhaled by that 1 person in 1 year. Assume we live in horizontal lava tubes 300m wide, let's say 10 meters of that tube per person to have some margin of error. That's <535 kg of CO2 in air in that section of the tube and ~8000 kg of CO2 captured in corn planted there the moment before harvest. It's doable IMHO. At least napkin math checks out.
    - loonster 5y ago
      Corn is a great plant optimized for production per acre. On the moon it may be more beneficial to optimize for carbon stability. Get plants with a more favorable Edible Carbon::Total Carbon ratio. A plant that can be harvested continuously would also be beneficial. The ideal plant may be something simple like grass. We can't eat it, so would need another intermediate step. Possibly Cows or Sheep. These would be grown for milk and not meat.
      - klondike_klive 5y ago
Jarwain 5y ago
if we figure out efficient methods for carbon capture planetside, couldn't we reuse those methods for any non-terrestial habitat?