Lunar Ice

Luna has water. We now know this is a fact. Not a lot of water and it’s probably in forms that could be difficult to extract. But it’s there. The real challenge isn’t technical. It’s having the foresight to use this scarce resource responsibly. Future Lunar Homesteaders will judge us harshly if we make the wrong choices.My primary concern is that many plans call for using Lunar ice to make rocket propellant. This is a short-sighted and irresponsible use of a precious and rare resource in my opinion. Lunar water, which is in limited supply, should be used exclusively for life support. Here are the reasons:

  • There are other propellant options that don’t require hydrogen and would be just as profitable. Cis-Lunar transportation does not require the high ISP that LH-LOX provides.
  • Lunar Homesteads are going to need lots of hydrogen for water production. It’s far more economical to extract it from Luna than it is to ship it from Earth (or asteroids eventually).
  • Hydrogen will also be needed for many resource extraction processes.
  • Liquid hydrogen is notoriously difficult to store.

We’ll need to develop new rockets to take advantage of resources that are plentiful on Luna instead of taking the small amount of hydrogen left on the surface. Check out the Transportation section for more information.

Lunar Ice Data

Resources (I’ve looked at)
  • Commercial Lunar Propellant Architecture – Long, in-depth analysis of what it would take to establish a profitable Lunar propellant infrastructure using polar ice. It’s really good and definitely worth reading. The only point I really disagree on is that of using Lunar ice for propellant (see above). This plan is definitely NOT based on Lunar Homesteading principals. But ANYTHING that gets us back to Luna is worth doing. Good luck!
    • Their first key point is that all work is done by robotics. No humans are involved. This is the complete opposite of Lunar Homesteading. Robots working in space doesn’t inspire imagination and hope. Humans do.
    • The paper proposes processing 2,450 metric tons of water every year. This is a huge amount of water. Additionally, the plan requires 2.8MW of power. This plan is definitely not simple or small scale.
    • Polar locations may not be ideal for Homestead construction due to less basalt and iron oxides.
    •  Volatiles are important but it may be more efficient to plan on importing them instead of hunting for them. It’s great if we find them doing our other stuff though.
  • Direct evidence of surface exposed water ice in the lunar polar regions – It’s pretty technical but the paper shows that there is most likely some kind of surface ice in the areas of permanent shadow. Of course, this is using remote sensing so we won’t really know what is going on until someone sends a robot to find out.

Resources (I have not looked at)
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  1. Do you have any estimate on how quickly the lunar polar ice would be used up of used for propellant? My estimate is that it would be about 29,000 refueling of s XEUS-scale lander. So, it seems to me that a few thousand flights over a few decades would make only a small dent in the quantity of ice on the Moon.

    Then, if recycling water at ISS rates (93%) the estimated 600 million tonnes of lunar polar water would last a lunar city of 1,000,000 people about 1,600 years. This ought to be plenty of time to develop the ability to import asteroids resources.

    • My primary concern is the human habit of sticking with inefficient (or harmful) systems once they are established. The current thinking is that we’ll use hydrogen burning rockets at first but will switch to a propulsion system that doesn’t use hydrogen later. But history has shown that entrenched systems are hard to replace. We can avoid the problem entirely if we spend a little time researching alternate propulsion (LOX/metal is one). Then we’ll be able to put in an efficient transportation system in from the start and we can save all the hydrogen for settlement expansion.

      As to how much Lunar ice exists, we just don’t know. Remote sensing only takes us so far. We won’t know until we start landing sensors in those regions. And I just can’t reconcile literally burning away hydrogen now and forcing future Lunar settlers to import it later. It’s short-sighted. Especially since it’s unnecessary. Future Lunar inhabitants will not thank us.

      I think it’s better to design systems that preserve limited resources, even if there is a lot of ice (and in an easily usable form). Simply going after the easiest resource to exploit it for profit is the same old thinking that has always caused us problems. We can do better this time.

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