Lunar Homestead Experimental Location

Version 1.2 August 18, 2023

The Lunar Homestead Experimental Location is the Apollo 12 landing site.

NOTE: This was written before I came up with the SPORE concept. Originally, I was only concerned with the regolith. Now, I’m focused on mining and building in the mega-regolith and avoiding the regolith as much as possible. However, most of this data still applies as the chemical make-up of the regolith is dependent on the chemistry of the mega-regolith. Apollo 12 is still the best choice for a default location.

Why select an Experimental Location?

The reasons why Lunar Homestead is focusing on a single location are:

• It reduces the number of variables we’ll need to deal with. The Lunar regolith is highly variable between locations. Picking a single site will narrow things down considerably and make it easier to conduct experiments and build equipment.
• We have physical samples from 9 locations. We can safely ignore the 3 Luna sites as they returned a single small sample each. Fortunately, Apollo returned many samples from the area surrounding each landing site. Physical samples give us a much better picture of the local geology than remote sensing (don’t get me wrong, remote sensing is awesome!). Our test location needs to be one of the Apollo sites.
• We can focus on the best possible conditions to find Lunar iron in usable concentrations and forms. This will allow us to optimize the equipment for that location. We can then tweak the gear to work in all locations. This gives us the best chance for success.

Which Apollo landing site?

So which Apollo site should we focus on? Let’s look at some parameters.

Free metallic Lunar iron

Free metallic Lunar iron is the first type of iron we should be looking for. It should be the easiest form to extract from the regolith and to refine into usable iron. Remember, FeNi metal particles are found in concentrations of less than 1% (by weight) everywhere (2, pg 160). The key is that most of this iron (the nanophase component) is found in agglutinates. Iron fines make up such a small percentage of regolith that it’s not worth hunting for them (we’ll use them when we find them). So we need to look for agglutinates.

Agglutinates are also important because they can trap solar wind gases that our Homesteaders need (3, pg 439). Some may even contain water. We’ll need to incorporate ways to capture these gases when we process agglutinates for iron. But that’s a future challenge, once we figure out how to make containers for those gases.

Which Apollo sites have the highest concentrations of agglutinates? Agglutinates make up 5% – 65% of the Lunar soil, with an average of 25% – 30% (1, pg 298). So we can get agglutinates everywhere. What we’re looking for is that one place where we get the most agglutinates for the least effort.

We’re looking for mature regolith. The more mature a soil is (meaning the longer the soil is exposed to space weathering), the higher the agglutinate content (4, pg 267). But not just any agglutinates. Agglutinates are a complex mixture of nanophase iron, glass, AND mineral particles broken from the surrounding rocks. We’re going to want mineral particles that contain the highest amounts of iron. Plus, more iron is formed during agglutinate formation when the surrounding rocks are iron-rich.

So we’re looking for places that are rich in ilmenite and have an abundance of agglutinates. Olivine, spinel, and pyroxene are also important but we won’t move on to those until we’ve mastered free metallic iron and ilmenite.

A Global Lunar Landing Site Study to Provide the Scientific Context for Exploration of the Moon gives the following data:

• Mare (Apollo 11 and Apollo 12) Agglutinates = 47%
• Boundary (Apollo 15 and Apollo 17) Agglutinates = 45%
• Highland (Apollo 14 and Apollo 16) Agglutinates = 45%

Ilmenite

Ilmenite is our “go-to” iron oxide mineral.

• It’s the most abundant oxide mineral.
• It contains iron, oxygen, and titanium. We’re going to eventually need all three.
• It may be the “easiest” mineral to extract iron from.

Where is the most ilmenite?

• Lunar Sourcebook
  • Apollo 11 and Apollo 17 mare basalts are up to 15%-20% ilmenite (by volume)(1, pg 140).
  • Proportion of ilmenite (volume %) from Lunar samples. (90-20μm, not including fused-soil and rock fragments) (1, pg 123)
    • Apollo 11 – 6.5
    • Apollo 12 – 2.7
    • Apollo 14 – 1.3
    • Apollo 15 (Highlands) – 0.4
    • Apollo 15 (Mare) – 0.8
    • Apollo 16 – 0.4
    • Apollo 17 (Highlands) – 3.7
    • Apollo 17 (Mare) – 12.8
    • Luna 16 – 1.8
    • Luna 20 – 0.0
    • Luna 24 – 1.0
• A Global Lunar Landing Site Study to Provide the Scientific Context for Exploration of the Moon (3, pg 432)
  • Mare (Apollo 11 and Apollo 12) Ilmenite = 3%
  • Boundary (Apollo 15 and Apollo 17) Ilmenite = 4%
  • Highland (Apollo 14 and Apollo 16) Ilmenite = 1%
• Handbook of Lunar Materials
  • Abundance of ilmenite (percent volume) in Lunar materials (4, pg 53)
    • Mare basalts = 0%-25% (high-Ti basalts contain more ilmenite than low-Ti)
    • Anorthositic rocks = trace only
    • Fragmental breccias (>25 micrometers across) = 2%-12% (depends on local rock type)
    • Crystalline breccias = 1%-2% (limited to highlands only)
    • Soil = 0.5%-5% (depends on local rock type)
  • Iron content (percent weight) in typical Lunar ilmenite (4, pg 54)
    • Mare = 44.88%
    • Highland = 37.38%
  • FeO concentrations in opaques (mostly ilmenite)(percent weight)(2, pg 29)
    • High-Ti mare basalts = 14.9% – 45.7%
    • Low-Ti mare basalts = 44.1% – 46.8%
    • Highland rocks = 11.60% – 36.0%
  • Ilmenite in mare basalts (percent content) (2, pg 34)
    • Apollo 11 mean
      • Modal (thin slice analysis) = 14.5%
      • Normative (chemical analysis estimate) = 21.1%
    • Apollo 12 mean
      • Modal (thin slice analysis) = 10%
      • Normative (chemical analysis estimate) = 7.5%
    • Apollo 15 mean
      • Modal (thin slice analysis) = 2.6%
      • Normative (chemical analysis estimate) = 4.1%
    • Apollo 17 mean
      • Modal (thin slice analysis) = 20.4%
      • Normative (chemical analysis estimate) = 23.7%
    • Average = 11.5% (Space Resources: Vol 3 Materials, 35)
    • Average (minus Apollo 15) = 14.4%

What does all this mean? First, you can see that the numbers are all over the place. The Lunar regolith is a really complex mix. The numbers aren’t going to help us much. So, what can we deduce from this data? Mare basalts are where we want to look for ilmenite. Highland rocks just have less iron and less ilmenite.

Site selection

Let’s look at the Apollo landing sites:

• Apollo 11
  • Landed in Mare Tranquillitatis (“Sea of Tranquility”).
  • The mare is primarily basaltic, similar to Earth basalts but containing much more titanium (5). Higher titanium concentrations are correlated with higher iron concentrations.
  • Apollo 11 brought back the least amount of samples and at least some of them were contaminated before they made it back to the lab.
  •  Possible candidate.
• Apollo 12
  • Landed in Oceanus Procellarum (“Ocean of Storms”) > Mare Cognitum (“Sea that has Become Known”) > Statio Cognitum (“Anchorage that has Become Known”).
  • Younger and of a slightly different composition than the Apollo 11 landing site (5).
  • Located next to Surveyor Crater, which may provide access to other valuable minerals.
  • The mare is basalt but with much less titanium than the Apollo 11 site.
  • Possible candidate.
• Apollo 14
  • Landed in the Fra Mauro Formation. Highlands, not mare.
  • Primarily ejecta material from the impact that formed the Imbrium Basin.
  • Some basalts but higher in aluminum and potassium (5).
  • Not a candidate.
• Apollo 15
  • Landed in Mare Imbrium. Near the Appenine Mountains and Hadley Rille.
  • The mare is basalt but with less titanium, similar to the Apollo 12 site (5).
  • Volcanic glass was also found in some of the samples.
  • Not a candidate.
    • The site itself is in a small valley with limited access to mare basalt.
    • Even worse, access to Mare Imbrium is cut off by Hadley Rill. We could move to the other side of the rill but then we negate the advantage of having data from physical samples.
    • The surrounding mountains would probably cast shadows over the Homestead, extending nightspan. We need more hours of sunlight, not less.
    • I think this site would be a really good candidate for Homesteading in general. The region is geologically complex with a wide variety of potential resources. We could do some very interesting things inside Hadley Rill with the right technology and Lunar industrial base.
• Apollo 16
  • Landed in Cayley Plains, a highland region.
  • Almost every sample was breccia, not basalt (5).
  • Not a candidate.
• Apollo 17
  • Landed in Mare Serenitatis in a deep, narrow valley.
  • Primarily, basalts with mostly high concentrations of titanium (5).
  • Clementine observations, and some samples, place the titanium concentrations much lower (5).
  • Access to highland rocks and volcanic glass.
  • Not a candidate.
    • A deep, narrow valley might provide radiation and impact protection. It might also limit the amount of sunlight a Homestead receives.
    • It’s also quite a trek to get to out into Mare Serenitatis and with what looks like a scarp blocking the way. My concern is that this site doesn’t have access to large areas of iron-rich mare basaltic regolith.

Great. That leaves us with Apollo 11 and 12. To narrow it down further let’s look at some Clementine data.

Right off the bat we can see that the nearside has far higher concentrations of iron oxides than the farside. And that most of the nearside concentrations are in the maria. That jibes with what we already know.

I’ve cropped and blown up the Clementine data image and added the Apollo landing sites. I did this by hand so please don’t get all twisted if you think I should have moved a certain diamond a smidge to the left. This wasn’t meant to be exact. I also kind of regret using a green diamond. I thought I was being clever (tying it into the LH logo) but all I did was make it a little harder to read. Oh well.

What does this image tell us? Three things:

• I’m not very good with Paint.
• Apollo 11 and 17 seem to have the highest concentrations of iron oxide. Apollo 12 and 15 don’t look too hot (but that could just be my poor placement). Apollo 14 and 16 have the lowest concentrations.
• The really interesting places are NOT Apollo landing sites! The Sea of Tranquility and the Ocean of Storms seem to have the highest concentrations of FeO. Too bad we don’t have any physical data to go with the remotely collected data. Maybe future Lunar Homesteaders will prospect these areas and discover the iron motherload!

How does the Lunar Prospector data compare to the Clementine data? Lunar Prospector used a neutron spectrometer to gather mineral data while Clementine used spectral reflectance (7). Apparently the two data sets correlate well (7). I recommend reading the paper (resource 7) if you’re interested in the science and math behind the conclusion. It’s really interesting. The main thing we need to know is that the researchers achieved several correlation coefficients, depending on the region they were looking at.

• The overall correlation coefficient = 0.811
• Removing the poles (keeping the area between +60º and -60º) = 0.887
• Constraining the data further (40° to 180°E longitude, ±60° latitude) = 0.930 (this doesn’t include any Apollo sites)
• Just the nearside maria (90°W to 90°E longitude, −30° to 60° latitude) = 0.941. This area covers everything we’re looking at.

A correlation coefficient is simple. A value of 1 is the strongest correlation possible. A value of 0 means there is no correlation. And a value of -1 is the strongest negative correlation possible. A correlation coefficient of 0.941 indicates a strong correlation between the Lunar Prospector and Clementine data. It’s good enough for me.

Another paper (source 9) states that the Lunar Prospector gamma-ray spectrometer data also supports the neutron spectrometer and Clementine data for iron oxide distribution. The paper is pretty technical but a cool read. One thing to note is that the aluminum and iron spectral lines are very close to each other. This means that high concentrations of aluminum can read like high concentrations of iron. Something to look out for.

This is a FeO distribution map made from Lunar Prospector data. It looks pretty similar to the Clementine map. And look at that bright yellow spot in the Ocean of Storms! That looks intriguing.

Where does this leave us?

With 2 choices:

Apollo 11

• Flat with relatively few craters and boulders.
• Located close to the equator (minimum energy required to launch and land).
• Nearest mare/highland boundary is 40 km away (1, pg 610). A small fraction of the samples returned (a few percent) consisted of highland mineral fragments (breccia)(1, pg 610).
• The age of the mare basalts range from 3.88 to 3.57 billion years (1, pg 610).
• There are at least two chemically distinct groups of basalts with differing ages (1, pg 610).
• Apollo 11 brought back 22 kilograms of material, including 2 core tubes, during a single 2.5 hour EVA (5). The core tubes sampled up to 13 centimeters below the surface (5). One large bulk sample makes up 15 kilograms of the total returned material. Due to time constraints, all of the samples were taken from the area close to the lander.
• Estimated regolith thickness (based on seismic data) is 4.4 meters (10, pg 229).

Apollo 12

• Flat with relatively few craters and boulders. Fewer craters than the Apollo 11 site.
• Located close to the equator (minimum energy required to launch and land).
• The Surveyor 3 spacecraft is nearby as well as Surveyor Crater.
• Mare basalts are younger than the Apollo 11 site and have a reddish color (1, pg 610).
• At least three chemically distinct groups of mare basalts (age 3.29 to 3.08 billion years)(1, pg 610).
• One sample contained KREEP (potassium, rare-earth elements, and phosphorus)(5).
• Copernicus Crater isn’t too far to the north. Who knows what we would find there.
• Apollo 12 brought back 34 kilograms of material, including several core tubes, during 2 EVAs lasting a total of 7.5 hours (5). The core tubes penetrated as much as 40 centimeters below the surface (5).
• The samples were almost all basalt (only 2 breccia were in the samples)(5). The basalts were predominately pyroxene and plagioclase, but also included ilmenite and olivine (5). There is also much less titanium in the Apollo 12 samples than in the Apollo 11 samples (5).
• Estimated regolith thickness (based on seismic data) is 3.7 meters (10, pg 229).

The verdict

This was a tough decision. Both sites are very similar. And both suffer from limited samples and a limited sample area (no rover on these missions). The processing and analysis of many samples is, at best, confusing. I feel like I need to look at all the data and analysis of each sample and put it all into a spreadsheet that I can understand. Talk about a project.

And honestly, I really thought about ditching both and heading into that iron hot spot deep in Oceanus Procellarum. But the limited information our physical samples provide us is better than no information at all (except remote sensing data that hasn’t been ground-truthed yet).  Maybe next time.

Apollo 12 is the official Lunar Homestead Experimental Location. Why?

• There are slightly more samples taken over a slightly larger area.
• Almost all of the samples were basaltic. That’s what we’re looking for.
• I checked out the Lunar Sample Atlas (www.lpi.usra.edu/lunar/samples/atlas/) and did a brief scan of a few samples from each site. The Apollo 12 samples seemed to have more ilmenite and olivine. Granted, this was a quick and non-scientific study.
• The samples also seemed to have more variety than the Apollo 11 samples. That’s probably a result of having a limited sample base though.
• It’s in the Ocean of Storms, which I think sounds cooler than Sea of Tranquility.
• I realized that it doesn’t really matter. I spent hours staring at photos and reading passages from the Lunar Sourcebook and other resources. Both sites are really similar so I just needed to pick one and move on.

OK Statio Cognitum, let’s see how much we really know about you.

Resources

1. Lunar Sourcebook (www.lpi.usra.edu/publications/books/lunar_sourcebook)
2. Space Resources: Vol 3 Materials (www.lpi.usra.edu/lunar/strategies/SP509-3-Materials.pdf)
3. A Global Lunar Landing Site Study to Provide the Scientific Context for Exploration of the Moon (www.lpi.usra.edu/exploration/CLSE-landing-site-study/)
4. Handbook of Lunar Materials (ntrs.nasa.gov/search.jsp?R=19800007749)
5. Lunar and Planetary Institute – Apollo Missions (www.lpi.usra.edu/lunar/missions/apollo)
6. NASA ISRU Technology Development Project (isru.nasa.gov/MetalsfromRegolith.html)
7. Lunar Fe and Ti Abundances: Comparison of Lunar Prospector and Clementine Data (science.sciencemag.org/content/281/5382/1493.full)
8. Indian Institute of Science – Centre for Ecological Sciences (ces.iisc.ernet.in/hpg/envis/Remote/section198.htm)
9. Global Elemental Maps of the Moon: The Lunar Prospector Gamma-Ray Spectrometer (science.sciencemag.org/content/281/5382/1484.full)
10. Lunar Stratigraphy (www.lpi.usra.edu/publications/books/lunar_stratigraphy/chapter_6.pdf)