A Handful of (Lunar) Dust

Last month, I was absolutely privileged to be invited to write a blog post for PTScientists, a German team competing to win the Google Lunar X-Prize. They are currently working on a landing vehicle that will transport their rover from sun-synchronous Earth orbit to the lunar surface, and I was honoured to take up their offer. Huge thanks to Sven, Robert and Karsten, as well as everyone else in Berlin. Here is the full text of that piece.

Apollo Landing Site

This is the landing site of Apollo 17. These pictures were taken on that mission, the last time humans walked on the Moon. For over 40 years it has sat abandoned, in some state of disrepair. I say ‘some state’ because we don’t know what the site looks like today. In fact, we have no idea what any of the Apollo sites look like, because NASA has never deemed it necessary to send anything to look. In fact, NASA has never returned to the Moon’s surface. The only missions to have landed after the date of Apollo 17 are the Soviet vehicles Luna 21 and 24, and the recent Chinese mission Chang’e 3. But none of these missions have gone back to the site of another landing.

It’s time to change that.

PTScientists are a small team (by space standards) based in Germany, but with support from scientists and engineers globally. Their mission is simple. Go back.

I mean, not them personally. A rover that they are building. But that rover will, if all goes according to plan, be studying the remains of the Apollo 17 landing site by 2017. Plus, if all goes according to plan, winning the $30 million Google Lunar X-Prize.

But why the moon? Surely it would be a better use of resources to accelerate the race to a manned landing on Mars? That is, after all, the long-term goal of most space agencies.

But the Moon has something special. It is close, easy to get to, and it has the regolith.

When I use the word regolith, what I basically mean is soil. But regolith sounds much cooler that soil, and is also the technical term for the layer of loose material covering a celestial body. Soil, basically. On the Moon, that means a layer between 3 and 15 metres thick of loose material. The regolith varies in size, from boulders to pebbles to gravel to a fine dust, all of it eroded over millennia by solar radiation and impact from micrometeorites.

That dust, the top few centimetres of the regolith, has some very interesting physical properties. The dust is so fine, it passed through the gloves of the Apollo astronauts and coated their hands in a fine black powder. Some of these particles are less than 2µm across, which is finer than the very finest particles in clay. When this dust is hit by micrometeorites, it sometimes forms tiny glass beads that heat the dust enough for tiny grains of elemental iron to form. Those grains are enough to make some of the grains slightly magnetic, enough to pick them up with a magnet in the low gravity of the Moon.

Regolith is not unique in the solar system. We think that most rocky bodies have it, including Mars, the Moon and comets. But unlike asteroids and comets, the Moon is already in Earth orbit and is easy to get to. And once you get there, you have access to a lot of material. And that material is very useful.

Lunar regolith is useful for three main reasons.

Vehicle

Lunar regolith can be made into rocket fuel.

Lunar regolith is about 7% aluminium, and more than 40% oxygen. Aluminium is a core component in a number of rocket fuels, and can even be mixed with water in particulate form to make a solid propellant (called ALICE). And oxygen can be used, super cooled, to make oxidiser. So in theory, the Moon can be used as a giant fuel depot – for oxidiser and propellant, the 2 components of rocket fuel. We could fuel interplanetary ships or build much larger deep-space probes to go to the outer solar system without having to carry the fuel to orbit. Because, if you want to take any mass into orbit, you need spend a lot of money on the launch vehicle – and a large proportion of the weight of any interplanetary vessel is fuel. But we could reduce those costs massively, by having all the fuel in space already. The costs of getting an empty ship to lunar orbit aren’t massive, and the costs of carrying fuel from the Moon’s surface to orbit are also relatively low. So we could massively increase the number and size of ships (both robotic and, hopefully, manned) leaving Earth for the rest of the Solar System. We could fuel the future of our exploration of the Solar System with the Moon.

Lunar regolith contains minerals that can be sold at vast profits.

Lunar regolith contains, broadly, the same materials as the Earth’s crust. However, it does contain much higher-than-Earth levels of titanium, and helium-3 – a potential fuel for nuclear fusion. And both of those can be sold, at great profit, on Earth. Even if you consider the costs of shipping equipment to the Moon and shipping the products back to Earth, you can still turn a considerable profit.

Now, the prospect of commercial mining of the Moon is advantageous (assuming you think colonisation is a good thing – which I do) for two different reasons.

If mining companies are setting up shop on the Moon, they will probably want to have an extensive operation – multiple sets of mining, refining and returning stations for whatever is being mined. And if you have a complex system in an extreme environment, you will bet that things will go wrong pretty frequently. And at some point, the companies are going to decide that having a crew of engineers living at the station for long shifts is cheaper than using robots. So bingo, suddenly you have a commercial drive to put a permanent human settlement on the Moon. And when there is commercial drive and money to be made, you can bet that things will really get moving.

And secondly, if companies are mining huge amounts of platinum/titanium/helium on the Moon, they’re going to have to sift through a lot of regolith to find it. So there are going to be enormous spoil heaps of aluminium, silicon, nickel and iron oxides (ores) just sitting on the surface of the Moon. And there you have the basic materials for building…basically anything. Computers, spaceships, bases – all sitting there. And then it would just take one company to start exploiting that, and we could have vast manufacturing sites on the Moon. But I’m getting ahead of myself.

I think it would be interesting to see how we, as a society, would respond to a large scale production centre on the Moon. But one thing is certain. If there is profit to be made, and the risks and costs are low enough, mining in space will happen. And some day, in the not too distant future, we might be seeing an advert like this on TV.

Lunar regolith has all the materials for construction

This is, in my opinion, the most exciting use for the abundant supply of lunar regolith – using it to build things. That could be large things, like robots and components for interplanetary ships. But more likely, it will mean building components for bases that are too large or unwieldly to ship from Earth easily – like large antenna or structural components for buildings, or simple roads to make travel quicker. And while this won’t be everything needed to build a colony from the ground up, it opens up the option for much larger-scale construction with lower costs.

The ability to build your own components is great, because shipping everything from Earth is expensive, time-consuming and highly limiting. Using local materials for your own purposes is called In Situ Resource Utilisation, and means you can develop the beginnings of a semi-independent colony – and is the Holy Grail for colonisation programs.

But in-situ construction is about more than colonisation. It opens up the possibility of building entire interplanetary ships on the Moon’s surface (or in orbit), using the iron and aluminium for the exterior of the ship and the silicon for the computers. Sure, we might have to ship some specialist materials and components to lunar space, but we could save on at least half of the weight of the ship (I can’t find reliable numbers for how much of the ISS is these simple elements) if the spacecraft were designed to use these materials. And that is without the considerations of fuel – which could all be delivered from the lunar surface.

But that’s a long way off. As it is, the major goal is finding a safe, reliable and cheap way to convert dust into spaceships – or the basic materials for building spaceships. And as it turns out, there are four main ways (that we know about) of doing that.

Refine the regolith into aluminium and iron for use in whatever

It is, it turns out, possible to convert lunar regolith into purified iron using very few materials and the thermite reaction. The thermite reaction is awfully fun, as it involves high temperatures, flying sparks and molten metal.

But as well as that, it is extremely useful. It allows for production of metals in remote conditions (like country train tracks, where the reaction is frequently utilised to join track sections) and is reasonably cheap. And conceivably, such a reaction would be possible on the lunar surface.

Essentially, the thermite reaction goes like this.

Pure reactive metal + less desired metal oxide + heat -> reactive metal oxide + pure desired metal

Remember, regolith is mostly made from iron oxides and aluminium oxides. Getting pure aluminium is relatively easy using electrolysis (we could power this with solar panels or nuclear reactors). So…

Pure aluminium + iron oxide + heat -> aluminium oxide + pure iron

So, it is entirely possible to envision a production system on the surface, manned or otherwise, producing significant amounts of both iron and aluminium for use or sale. It wouldn’t be easy or cheap, but it’d be lot better than shipping the materials from Earth.

But there might be another way to create structures on the lunar surface.

3D printing! On the Moon!

Even if this isn’t as practical as other ideas, it definitely wins the prize for the coolest. 3D printing is one of the most versatile manufacturing techniques ever created, and the potentials for it on an off-world colony are almost limitless. 3D printing allows for in-situ manufacturing of virtually any component for bases, ships, robots – everything.

The problem is, moon dust is not the best material for 3D printing with. You first need to convert the regolith into either pure metal oxide (see above) or a plastic-like material that can be easily melted and reformed.

Now, ESA is seriously considering this option for the ‘Moon Village’ that they have in the pipeline. They have a prototype machine that can take in a load of regolith, put it into a specific shape and spray a binding agent onto the whole thing, forming a hollow dome with an airlock and windows.

However, this plan does have one big fat flaw – it involves shipping several tonnes of additive and binding agent (magnesium oxide and a salt of some sort) to the lunar surface. Which is time-consuming and expensive. What if we could build bases using materials native to the lunar surface, with no additives at all?

3D printing with metals is actually a bit different to regular, plastic 3D-printing. A plastic printer (the kind that you are probably familiar with) works by inserting tiny ‘pixels’ of plastic at certain points in 3D space, thus building a 3D structure.

But to 3D print metal, a different technique is used. A ‘bed’ (as the base of the printer is called) is covered with a layer of metal oxide of uniform thickness. A laser then runs over the bed, heating up the areas that are being printed. This reduces the oxide, forming a ‘pixel’ of solid metal. Another layer of oxide is then added, and the laser forms the next layer, slowly building up a 3D shape – something like this.

In order to do that, a fine powder of metal oxide is needed. But wait – we have an incredibly fine powder on the Moon’s surface, consisting mostly of aluminium and iron oxides. And how do we separate those? A good, old fashioned magnet. Using a magnetic gathering device, a store of fine iron oxide dust could be obtained on the Moon’s surface, and used to 3D print metallic structures and components.

Using a microwave to solidify (sinter) the regolith

This is, on the surface, much less exciting that the other ways of building on the Moon. There are no lasers, no 3D printing, and no exciting reactions. But there is the potential to build huge, solid structures – and to do so with extremely low costs. Microwaves. The radiation kind, not the cook-frozen-food kind.

Way back at the start of this, I mentioned that the regolith contained tiny particles of solid iron. Using the right frequency of microwave, it is possible to melt those granules without even touching the lunar surface. Elemental iron is acted upon by microwaves, and so microwaves can be used to heat these iron particles without acting on the rest of the regolith. And like most things, when that elemental iron is heated to extreme temperatures it melts and begins to flow. But when the microwave turns off, the iron cools and solidifies. And when the iron solidifies, it solidifies the rest of the regolith with it.

The best way to imagine this is a bowl of lumps of chocolate and gravel. When it’s all separate it might not be the most fluid, but it can definitely move around. Now what happens when you put that bowl in the microwave for 30 seconds? The chocolate melts and flows to fill the gaps in the gravel, encasing it. When the chocolate cools again, you will be left with a lovely block of chocolatey gravel. A single, solid lump. The exact same is true of microwaved regolith. If you run a beam of microwaves over a layer of regolith for about 30 seconds, it melts the iron and, on cooling, forms a concrete-like substance. Strong, incompressible, excellent at blocking radiation. In short, all the properties you need for a lunar base building material.

At least, in theory. The microwave sintering has worked in a lab, using a sample of regolith left over from Apollo, but whether or not it works in situ, with a low-powered beam, is still questionable. But if it works, it opens up the possibility of massively cost-reduced colonies. A bulldozer-type device piles up an area of fine regolith and microwaves it to form solid material. It piles on another layer and does it again. In fact, using an inflatable framework, this kind of production technique could be used to build the exact kind of ‘lunar cottages’ which ESA is proposing, but without the cost of shipping additives all the way to the lunar surface.

In fact, microwave sintering could have a few other applications, as well as habitat construction. When the regolith is heated, some trace elements are released from the regolith in the form of gas. Some of these are useful for a colony (carbon and hydrogen) and some are potentially profitable (helium, including helium-3). And lo and behold, we have circled right back to mining the Moon for profit. As well as this, sintering could be used to build roads around a lunar base. Lunar travel across a dusty, loose surface is difficult on foot or with large vehicles, and the huge amounts of dust that this generates are a potential health hazard. But if a lunar buggy were to be equipped with a wide microwave beam and rolled slowly over the surface, it would make a track of hard, dust-free surface that is ideal for moving around on safely.

But in order to even consider that possibility, we need to work out if this technique is effective. Which is where PTScientists come into the equation.

The PT Scientists intend to win the Lunar X-Prize, make no mistake. But they also intend to get some science done when they get there as well. And one of the main experiments that will eventually be shipped on the Audi Lunar Quattro rover is a little microwave beam and a downward facing camera. Because we need to see if this microwaving technique actually works, before we spend hundreds of millions of dollars shipping a giant microwave-bulldozer-construction robot thing to the lunar surface. And if it does work (as all the predictions say it will) then it might open a window to a new age of mankind. An age where we can build lunar complexes the size of towns, for a fraction of the cost of carrying the parts with us. And large-scale lunar complexes in large quantities could be key in allowing us to set up permanent bases of operations in lunar space. Quite simply, microwave sintering could be the technology that allows us to take that vital first step and get a permanent, inhabited structure on the surface of the Moon.

Imagine that. In the next few decades (if funding and public interest stays roughly where it is), we could have humans living, for months and years at a time, on another celestial body. And it wouldn’t take us halfway to bankruptcy, because they could be making almost everything they need where they were – plus sending home shipments of rare materials. We could well be using products that contain lunar-origin metals and polymers. And most exciting of all, that colony could be feeding a steady stream of parts and fuel into lunar and earth orbit, building up the next generation of interplanetary spaceships. Using the Moon, we could take ourselves to Mars, and send a massive wave of research probes all over the Solar System. The second age of humanity, when we become an interplanetary species.

Not bad for a handful of dust.

Image Sources:

  1. https://en.wikipedia.org/wiki/Thermite#/media/File:Utah-thermite.jpg
  2. http://www.geek.com/wp-content/uploads/2014/03/6.gif
  3. http://33.media.tumblr.com/9242de34a2a385002e4b136d54791383/tumblr_inline_no02w23zBn1qzgziy_500.gif
  4. NASA
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