5 ms·

Yeah, but flipside, you're probably gonna need things on the Moon that you wouldn't for a terrestrial base. I think it's fair to assume that the $7bn a year fig

by ketzo 5y ago

Yeah, but flipside, you're probably gonna need things on the Moon that you wouldn't for a terrestrial base. I think it's fair to assume that the $7bn a year figure is just a very rough number, but still a useful one for understanding just how outrageously expensive it would be to maintain a Moon base.

jhgb 5y ago
You kind of have a model of a lunar space station in the form of ISS. That's definitely not 7000 tonnes of supplies for a base. Maybe something like 15 tonnes per year or so.
- ben_w 5y ago
  ISS currently has 7 people on it, McMurdo Station varies between 250 and 1258. I don’t know the mass/year of the ISS resupply missions, neither including or excluding orbit reboosting fuel which a moon base can clearly ignore.
  - 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.

by ketzo 5y ago

jhgb 5y ago

You kind of have a model of a lunar space station in the form of ISS. That's definitely not 7000 tonnes of supplies for a base. Maybe something like 15 tonnes per year or so.

ben_w 5y ago
ISS currently has 7 people on it, McMurdo Station varies between 250 and 1258. I don’t know the mass/year of the ISS resupply missions, neither including or excluding orbit reboosting fuel which a moon base can clearly ignore.
- 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.