6 ms·

I'll take a look at the exact figures, but assuming the average number of people at McMurdo is 750, it's 9 tonnes per person per year, whereas in the case of IS

by jhgb 5y ago

I'll take a look at the exact figures, but assuming the average number of people at McMurdo is 750, it's 9 tonnes per person per year, whereas in the case of ISS, it should be something like one third of this number per crew member at worst. Clearly they've already minimized the necessary supplies somewhat already.

Retric 5y ago
A big difference is the ISS uses 24/7 solar where McMurdo can’t. Unfortunately powering a moon base is quite difficult do to the month long day night cycle, so it’s going to need nuclear or a lot of batteries. That said, the ISS doesn’t do long distance missions dropping off equipment etc the way McMurdo and presumably any Moon Base would. So, the ISS isn’t that great of a model.
- jhgb 5y ago
  ISS doesn't use "24/7 solar". Insolation of the ISS depends on the beta angle and therefore ISS crucially relies on batteries for its continuous operation.
  - dredmorbius 5y ago
    That is splitting hairs. ISS has a 90 minute orbital cycle. It requires 45 minutes of power reserve. Not 14 days' worth. All else equal, a lunar base would require ~500x more energy storage if solar-reliant.
    - jhgb 5y ago
      Here's the thing about a lunar base on the south pole of the Moon: It's assumed that it would manufacture its own propellant from local resources (water). That means that you're already storing electricity electrochemically because that's exactly how you make propellant from water. But that means that it's just a small leap to make the storage tanks slightly larger and siphon off a small portion of the hydrogen and oxygen to generate "baseline" electricity for the station. You already have all the equipment anyway, why not just add a fuel cell? We can do small fuel cells more easily than we can do small reactors anyway. And even just one spare cubic meter of your hydrogen tank provides you with 1.3 MWh of electricity. One extra meter of length on a 4.5 diameter tank provides you with over 10 MWh of electricity.
      - ben_w 5y ago
        > You already have all the equipment anyway, why not just add a fuel cell? According to the blog post, the dry mass of the fuel cells would mass similar to LiIon of the same energy storage capacity, not counting the mining equipment to get the lunar water.
        jhgb 5y ago
        That makes no sense whatsoever; fuel cell mass scales with power output, not with system capacity. Extra capacity incurs just slightly bigger tanks. No serious study I've seen assumes that long-duration storage (~100h or more) has fuel cells heavier than batteries. The last paper I've seen had batteries twice as heavy as the whole fuel cell system. I may try to find it again.
        Retric 5y ago
        You need a system, the fuel storage tanks scale with energy storage. Also, mining might eventually allow you to scale, but still requires equipment.
        jhgb 5y ago
        You need a part of the system anyway so you can't count those parts (water tanks, hydrogen tanks, oxygen tanks, electrolyzer) into any of the power options. They will be there regardless of whether you want them or not. Also I've noticed that despite of what ben_w claims the article says, the article still assumes 100 kWh/t for a battery system and 1 MWh/t for a fuel cell system. So it doesn't really say that "the dry mass of the fuel cells would mass similar to LiIon of the same energy storage capacity", otherwise the numbers would be in the opposite order.
        Retric 5y ago
        Due to shipping and redundancy concerns redundant tanks are used to expand storage. So, the dry mass of tanks should scale nearly linearly with the total amount of water, hydrogen, and air stored.
  - Retric 5y ago
    As dredmorbius points out, the ISS gets solar every hour of every day, so it really is 24/7. What it’s not is 60/24/7, because up to ~45 minutes of each hour may be in earths shadow.
    - jhgb 5y ago
      I may not be a native English speaker, but Wikipedia tells me that "In commerce and industry, 24/7 or 24-7 service (usually pronounced "twenty-four seven") is service that is available at any time and usually, every day ... Synonyms include round-the-clock service (with/without hyphens), especially in British English, and nonstop service". I struggle to fit "at some times during every hour" into this definition. If there's a 24/7 shop, I definitely don't expect not being able to enter it at some times, or even not being able to enter it 75% of the time.
      - Retric 5y ago
        In practice it’s common to use similar terminology for intermittent services. For example a subway train might only be running every 30 minutes but it still lists hours of operation. The hotel help desk might not have someone there every second, but theirs a difference between someone putting up a “be back in 15 minutes sign” when their on a bathroom break rather than a closed sign when they are leaving for the day. Informally, the existence of a modest wait doesn’t preclude 24/7 service.
        jhgb 5y ago
        I definitely don't picture a 24/7 service as waiting up to 45 minutes every hour. By that time you're operating six hours out of every twenty four. You might not even be able to advertise yourself as 24/7 at that point in some places. > For example a subway train might only be running every 30 minutes but it still lists hours of operation. But that's a train. It never runs every single moment, so that doesn't make the times with once-per-30-minutes trains different from the times with once-per-10-minutes trains. On the other hand, if it's for example a grocery store, you definitely do expect being able to enter at any moment and purchase something if it advertises itself as "24/7" or "nonstop".

by jhgb 5y ago

Retric 5y ago

A big difference is the ISS uses 24/7 solar where McMurdo can’t. Unfortunately powering a moon base is quite difficult do to the month long day night cycle, so it’s going to need nuclear or a lot of batteries. That said, the ISS doesn’t do long distance missions dropping off equipment etc the way McMurdo and presumably any Moon Base would. So, the ISS isn’t that great of a model.

jhgb 5y ago
ISS doesn't use "24/7 solar". Insolation of the ISS depends on the beta angle and therefore ISS crucially relies on batteries for its continuous operation.
- dredmorbius 5y ago
  That is splitting hairs. ISS has a 90 minute orbital cycle. It requires 45 minutes of power reserve. Not 14 days' worth. All else equal, a lunar base would require ~500x more energy storage if solar-reliant.
  - jhgb 5y ago
    Here's the thing about a lunar base on the south pole of the Moon: It's assumed that it would manufacture its own propellant from local resources (water). That means that you're already storing electricity electrochemically because that's exactly how you make propellant from water. But that means that it's just a small leap to make the storage tanks slightly larger and siphon off a small portion of the hydrogen and oxygen to generate "baseline" electricity for the station. You already have all the equipment anyway, why not just add a fuel cell? We can do small fuel cells more easily than we can do small reactors anyway. And even just one spare cubic meter of your hydrogen tank provides you with 1.3 MWh of electricity. One extra meter of length on a 4.5 diameter tank provides you with over 10 MWh of electricity.
    - ben_w 5y ago
      > You already have all the equipment anyway, why not just add a fuel cell? According to the blog post, the dry mass of the fuel cells would mass similar to LiIon of the same energy storage capacity, not counting the mining equipment to get the lunar water.
      - jhgb 5y ago
        That makes no sense whatsoever; fuel cell mass scales with power output, not with system capacity. Extra capacity incurs just slightly bigger tanks. No serious study I've seen assumes that long-duration storage (~100h or more) has fuel cells heavier than batteries. The last paper I've seen had batteries twice as heavy as the whole fuel cell system. I may try to find it again.
        Retric 5y ago
        You need a system, the fuel storage tanks scale with energy storage. Also, mining might eventually allow you to scale, but still requires equipment.
        jhgb 5y ago
        You need a part of the system anyway so you can't count those parts (water tanks, hydrogen tanks, oxygen tanks, electrolyzer) into any of the power options. They will be there regardless of whether you want them or not. Also I've noticed that despite of what ben_w claims the article says, the article still assumes 100 kWh/t for a battery system and 1 MWh/t for a fuel cell system. So it doesn't really say that "the dry mass of the fuel cells would mass similar to LiIon of the same energy storage capacity", otherwise the numbers would be in the opposite order.
        Retric 5y ago
        Due to shipping and redundancy concerns redundant tanks are used to expand storage. So, the dry mass of tanks should scale nearly linearly with the total amount of water, hydrogen, and air stored.
- Retric 5y ago
  As dredmorbius points out, the ISS gets solar every hour of every day, so it really is 24/7. What it’s not is 60/24/7, because up to ~45 minutes of each hour may be in earths shadow.
  - jhgb 5y ago
    I may not be a native English speaker, but Wikipedia tells me that "In commerce and industry, 24/7 or 24-7 service (usually pronounced "twenty-four seven") is service that is available at any time and usually, every day ... Synonyms include round-the-clock service (with/without hyphens), especially in British English, and nonstop service". I struggle to fit "at some times during every hour" into this definition. If there's a 24/7 shop, I definitely don't expect not being able to enter it at some times, or even not being able to enter it 75% of the time.
    - Retric 5y ago
      In practice it’s common to use similar terminology for intermittent services. For example a subway train might only be running every 30 minutes but it still lists hours of operation. The hotel help desk might not have someone there every second, but theirs a difference between someone putting up a “be back in 15 minutes sign” when their on a bathroom break rather than a closed sign when they are leaving for the day. Informally, the existence of a modest wait doesn’t preclude 24/7 service.
      - jhgb 5y ago
        I definitely don't picture a 24/7 service as waiting up to 45 minutes every hour. By that time you're operating six hours out of every twenty four. You might not even be able to advertise yourself as 24/7 at that point in some places. > For example a subway train might only be running every 30 minutes but it still lists hours of operation. But that's a train. It never runs every single moment, so that doesn't make the times with once-per-30-minutes trains different from the times with once-per-10-minutes trains. On the other hand, if it's for example a grocery store, you definitely do expect being able to enter at any moment and purchase something if it advertises itself as "24/7" or "nonstop".