By Tim Ventura | 22 January 2020
NASA has a plan to return to the moon, but if we’re going to stay there, we’ll need a permanent home on the lunar surface. We’re joined by Ed McCullough to discuss his vision for a lunar colony inside a massive 25-mile diameter glass dome, and the engineering work he’s done to prove that it’s possible. Ed is a former Principal Scientist at Boeing, the former chairman of the AIAA Space Colonization Technical Committee, and Section-E chairman at the ISNPS STAIF conference, among many other honors & credentials he carries related to innovations in space colonization.
Ed, we’re finally going back to the moon, and NASA already has a plan to put a lunar station in orbit called Gateway, with the goal of facilitating trips down to the surface for research. You’ve been a long-time advocate of space colonization, and I wanted to start things out by asking whether the moon is the best place to begin in terms of colonizing space?
Not everybody agrees with me, but from my point of view the best place to start is the moon. The reason is that you’re close to the Earth, you’re in a gravity field to make construction easier, and you’ve got easy access to raw materials, and you can use local processing plants, etc.
In the moon’s low gravity, you’ve still got up & down, but you can easily move things around, put them into alignment, and they’ll actually stay where you put them during construction. It doesn’t mean you can’t construct a colony in space, you just have to use different techniques.
Now you’ve written a detailed engineering proposal for Boeing entitled “Establishing a Large Scale Colony Infrastructure On The Moon” which describes how to construct a massive lunar dome — but your project actually begins with the construction of underground habitats first. Why start underground and build the dome later?
You need underground habitats to protect yourself from the radiation, and several meters underground, the radiation levels are almost nothing, and there’s not much temperature variation either.
Starting underground is a very practical way to build a stable shelter on the moon — but it doesn’t mean you have to stay underground. Ultimately you’d live in a habitat on the surface, and use the underground shelter as a temporary retreat from something like a large solar proton event.
Living Underground on the Moon: How Lava Tubes Could Aid Lunar Colonization – Researchers have identified "pits" on the moon, which are likely lava-tube "skylights" — geological doorways to underground tunnels that were once filled with lava. @SPACEdotcom https://t.co/3LwmcGVLjf pic.twitter.com/EMlrvBAFp0
— The SETI Institute (@SETIInstitute) August 1, 2019
Underground habitats also offer fallback protection from a number of other unexpected events — for instance, like damage to an above-ground dome causing it to depressurize. In an event like that, you could actually save quite a bit of the atmosphere by using cryocondensation to condense the atmosphere in through apertures — but you’d still need a safe place for people to go.
Another advantage of going underground is that instead of having doors and apertures in the dome, you can simply go underneath the dome and take a subway to some other portal where you come out on the surface. That makes design & construction easier, and means the dome has fewer weak points in its structure.
Now, in terms of the dome itself, you’ve described building a dome 25 miles in diameter that’s up to 5,000 feet high in the center, but enclosed in S-Glass that’s only 17 inches thick. Can you describe that a bit for me?
S-Glass is a type of glass that’s literally stronger than steel — and what I’m saying is that the dome material required will need to be as strong as S glass that is 17 inches thick. Speaking practically, you can’t build an S-glass dome 17 inches thick with normal construction methods, but you can build other things equally as strong, which is the final form of the dome that I came up with.
Really my initial challenge was simply to determine whether it was physically possible to do this in the first place. I kept seeing a piece of NASA concept art being passed around in briefings showing a domed city in Shackleton Crater, and I was skeptical enough that I sat down one day to prove that it couldn’t be done. As it turns out, it’s actually feasible with a 17″ S-Glass dome.
So you’re saying that you set out to prove the dome wasn’t possible, but it sounds like in the end you proved yourself wrong — and that inspired you to keep working on it?
Exactly. Simply knowing the dome is possible doesn’t solve the issue of how to protect it from micrometeorites, falling rockets, etc. If you somehow built the dome as a single massive piece, accidental damage like that would destroy the whole thing — so I worked on a way to design it out of facets, which lets your replace damaged parts of the dome if required.
Another issue is moisture: S-Glass is unbelievably strong, but it cannot maintain its strength if it gets moisture on it, which means you’d have to protect it both from moisture on the inside as well as something like chunks of ice hitting it from outside.
Ultimately what this meant was coming up with something that’s heavier & much thicker than S-Glass, but the math works to balance the weight of the glass with the upward pressure of the atmosphere.
The faceted design I came up with has another advantage as well: it allows you to manufacture just a few simple tile designs that you can replicate repeatedly to tile the entire surface of the dome, which simplifies design & construction considerably.
OK, this brings us to self-organizing systems, which is something that you’ve written about using to build the dome with machines and what you’re calling “smart materials”, with something like the equivalent of barcodes on them.
Well, basically you’ve got two choices: either you use artificial intelligence & smart materials, or else you use astronauts with wrenches. For a city-sized dome on the moon, astronauts aren’t practical — you’ll need to use machines that can assemble the dome quickly & efficiently without risking people’s lives in the process.
This means you’ll need lots of robots, a good navigation system, and excellent metrology. The robots will also have to be agile, able to climb, carry heavy things, as well as line them up to bolt or weld them together. Add that all together, and you’re really talking about a self organizing system.
This idea of self organizing systems goes all the way down to the individual components being used. Forget bar codes — what you do is assign an IP address to every component in the project, including the tools used to build it. The robots know each other, they know the components, and they have the plans to put it all together — and as a human controller, you can just sit in front of a monitor & watch the dome build itself.
Once the dome is built, you need to pressurize it with a breathable atmosphere — and one of the difficulties there is that the moon doesn’t have enough nitrogen. Right?
Yeah. When I originally started working on this project, lunar nitrogen was suspected to be somewhere around a hundred parts per million. When you consider how much atmosphere is required for a dome this size, it means that finding the atmosphere is several orders of magnitude worse than the problem building the dome itself.
Fortunately, what’s happened in the meantime was that LCROSS actually hit the moon and we found out to a greater degree what was in those polar craters. I was hoping they’d contain ammonia, and they do, which puts the concentration of nitrogen much higher than a hundred parts per million. This ameliorates the problem to a greater or lesser extent.
OK, now in addition to atmosphere, you need power. You’ve described embedding solar panels into the dome, which allows it to basically generate its own power, right?
Yes, I’d say that around 20% of the area of the dome could be photovoltaic panels, but there are other things that could compete with that — such as transceivers to let you make the dome into a radio telescope, for example.
So essentially you can just take the dome area and multiply it by a number of factors to deal with view angles to the sun, and that lets you determine what your minimum and maximum power will be. Some of the power generated will be used directly, and the rest is put into storage for when you have low view factors to the sun.
You can store that energy in several different ways: the easiest is cryogenic, which means using a very large reservoir of a cold material, or you could take it the other direction and use a thermal well, meaning you could actually melt lunar regolith & use underground magma as a heat reservoir. Obviously you can use chemical storage batteries as well, it becomes a question of storage capacity vs. overall demand.
Well, with energy & atmosphere, I guess the only remaining component is water. What’s your plan to supply large amounts of water to the dome for the colonists to use?
Obviously there’s water at the lunar poles — but surprisingly, you’ll also find it at the lunar equator. You can make it by taking lunar regolith and heating it up, and it will give you 1 kilogram of water for each cubic meter of regolith.
Here’s how that works: hydrogen from the solar wind is absorbed onto the particles of regolith, and the surface area is so high that there’s maybe 60 to a hundred parts per million. You’ve also got iron oxide in the regolith, which means that by simply taking the regolith and heating it up, the hydrogen will reduce the iron oxide and produce steam, which can be condensed.
At the equator, that will give you a kilogram of water for each cubic meter of regolith, but at higher latitudes, you can increase that by a factor of 10x — giving you 10 kilograms of water. There’s even more at the poles, also: the lunar prospector data indicates you would get around 34 times water.
The really exciting data is from LCROSS, however, which produced readings on the order of 5.6% water, plus or minus around 3%. That gives you around 56 kilograms of water for every ton of lunar regolith, which is quite a bit of water. It’s more water than anybody needs.
If you’ve got water, atmosphere, and power, it sounds like that might be able to become completely self sufficient, which could be beneficial given the cost of transporting materials from Earth, right?
Well the water, atmosphere and the dome provide you with a basic living environment, but still have to eat — so true self-sufficiency would mean producing a range of plants and animals. That gets you into larger questions of building an ecosystem, which has its own challenges but isn’t impossible.
If you have water, you can also produce fuel, right? You’d mentioned ammonia being available, which might potentially be another fuel source. Does that sound accurate?
Yes, ammonia is good because it gives you a propellant that’ll actually stay in the tank without a whole lot of trouble. When you’re dealing with cryogens, you have to actually continuously cool them because otherwise they’ll change into a gas. With nitrogen, you can make a number of different types of storable propellants that will stay in a liquid form at normal atmospheric pressures without the refrigeration machines — so nitrogen allows you to make the storable propellants.
Since we’re talking about actually living on the moon, what about the health issue of micro-particulate dust getting into suits & airlocks, and potentially causing lung and respiratory issues?
That’s been an ongoing concern for a many years, but what I think people are missing is that the smaller these micro-shards of glass are, the more surface area they have. They’re basically composed of silicon oxides, which are very susceptible to fluorine — so I like to joke that you can solve the problem by mixing toothpaste in with the ceiling material, space suits, etc.
Speaking practically, what you need is something with free flourides that can be donated in order to destroy the silicon matrix on these particles. At around 60 microns, these look like an arrow head and they’ll actually create micro-perforations on your spacesuit. Adding a flourine donor will stop that, and dissolve the sharp edges on these particles, making them harmless.
— Fraser Cain (@fcain) May 5, 2018
Another health concern is muscle atrophy and bone density reduction from reduced lunar gravity. I’m wondering how much that would affect lunar colonists and what some potential solutions might be?
The issue of the physiological effects from low gravity is a problem, and that’s something that’s being worked on by NASA and others for space travel in general.
Several years ago, I was involved with a conference at the National Academy of Science, called “Research Enabled by the Lunar Environment” and many of the presentations involved ways to ameliorate space-related degeneration of muscles and the circulatory & nervous system. There’s definitely a problem, but there are also a lot of potential solutions.
With all of those things in place, what do you think the cost would be, and how long do you think it would take to build this lunar colony?
I’ve estimated that it would take around 15 years to build, and a lot of that time goes into creating the machines to build it and setting up energy generation systems on the moon to power them. Fortunately, the Moon has lots of solar power available, which you can collect and store in a surge pile, which allows you to buffer energy usage versus energy accumulation from the sun.
Now in terms of cost, there are a number of different business models that allow you to do things for the Earth that can actually bring in revenue, so the major cost hurdle is mostly in the initial construction phase of the project. Since you need to setup power generation on the moon anyways, we proposed generating a surplus and beaming it back down to rectennas on earth to offset the cost of construction, which would take about 13 years.
In other words, you’re talking about an initial upfront investment to colonize the moon, but over time this project would more than pay for itself.
We estimate that this project could increase the gross world product from roughly $40 trillion to around $860 trillion a year by selling power back to the Earth. So yes, there would be a large upfront investment, and it would take around 13 years until first light from the moon, but after that it pays for itself.
About Our Guest
Edward D. McCullough is a retired principal scientist at The Boeing Company and former member of the NSS Board of Directors. He received his professional training in nuclear engineering through the U.S. Navy, and Bettis and Knowles Atomic Power Laboratories (gaining his Certification for Nuclear Engineering at Pearl Harbor Naval Shipyard in 1975).
McCullough focused on concept development, experimental chemistry, and advanced technology at Rockwell Space Systems Advanced Engineering and at the Boeing divisions of Phantom Works and Integrated Defense Systems. He has researched innovative methods to reduce the development time of technologies and systems from 10 to 20 years down to 5 years. He has experienced successes in the area of chemistry and chemical engineering for extraterrestrial processing and photonics for vehicle management systems, and integrated vehicle health management and communications. He has led efforts for biologically inspired multi parallax geometric situational awareness for advanced autonomous mobility and space manufacturing.
McCullough has developed several patents, including patents for an angular sensing system; a method for enhancing digestion reaction rates of chemical systems; and a system for mechanically stabilizing a bed of particulate media.
McCullough is Chair Emeritus of the AIAA Space Colonization Technical Committee, a member of the Board of Trustees for the University Space Research Association, a member of the Science Council for Research Institute for Advanced Computer Science, and a charter member of the AIAA Space Exploration Program Committee. Mr. McCullough previously served on the NRC Committee to Review NASA’s Exploration Technology Development Programs, and the Planning Committee for the Workshop on Research Enabled by the Lunar Environment.
Reprinted with permission from the author.
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