Can we be “resourceful” on the Moon? (Part 1)
The solar wind implants gases into the lunar soil
While the resources of space have the potential to revolutionize spaceflight—giving us a much wider range of activities than are now possible, including habitation of other planetary bodies—discussions on various internet forums show that there is a lot of confusion and lack of knowledge about space resources in general and lunar resources in particular. To some, the idea of harvesting and using resources from a body other than Earth has a science-fiction aura—for them, air, propellant and food manufactured for people belongs on the silver screen, not in space or on other worlds.
So, what is a “space resource?” In broad terms it is needed materials or energy derived from space itself. The value of space resources is immediately obvious; at transport and delivery costs exceeding $20,000 per pound to low Earth orbit, everything we find and use in space is one more thing we do not have to pay exorbitant costs to transport. For human spaceflight, consumables are heavy but absolutely necessary. This category includes air, water, electrical power, and rocket propellant. On a long space journey, we could save millions to billions of dollars by re-fitting consumables in space rather than dragging them all up to orbit with us from the deep gravity well of the Earth.
Unfortunately, the materials and energy we need in space are not there in the form we need them. Thus, our task is to convert what we find into what we want. There’s nothing magical about this – modern industrial chemistry is largely concerned with this very topic. All you need to convert chemical substances in one form to another one is time and energy. Fortunately, both are available in quantity in space, especially if you use automation and robotics to perform a lot of this work. Creating systems to harvest and utilize space resources has the benefit of boot-strapping a self-sustaining, spacefaring capability instead of remaining tethered to never-ending, one-off expenditures and Earth’s gravity well.
For many years we have used energy provided by the sun to generate electrical power in space but we have yet to use any material resources. The Moon is the nearest object offering usable resources. Contrary to common belief, the lunar surface contains virtually all the elements one needs to create usable products for human space faring, including air, water and rocket propellant.
It’s often said that the Moon is resource-poor. That is inaccurate; the Moon is resource different. It is depleted in volatile substances (those that have very low melting points). The most important rare resource on the Moon is hydrogen. The Moon itself has very little of this element, but the soils have a great deal of it; because the Moon has no atmosphere or global magnetic field, the stream of protons from the Sun (the solar wind) implants hydrogen onto the surface of the dust grains on the Moon. This solar wind hydrogen can be released through heating of the dust. When you have both hydrogen and oxygen, you have air, water, and rocket propellant.
The typical hydrogen concentration in most soils is 20 to 100 parts per million. This is enough quantity to extract and use, especially if much of the mining and processing work is done through robotic machines operated from Earth. Hydrogen appears to be present in higher quantities in soils that have high titanium content, which are abundant on the lunar near side (the Apollo 11 landing site has one of the highest titanium contents found on the Moon to date).
Now there are even more exciting resource prospects. The Moon has abundant hydrogen at the poles, enriched by more than a factor of three over the global average. Some of this hydrogen, present in the permanently dark and cold floors of polar craters, may be in the form of water ice. Additionally, with the spin axis of the Moon perpendicular to the plane of its orbit around the Sun, some peaks near the poles appear to be in near-permanent sunlight, permitting continuous collection and use of solar electrical power, as well as the important benefit of a near constant surface temperature.
For these reasons, recent international exploration of the Moon has focused on the poles of the Moon, where extracting and using lunar resources is easiest and where humans have the greatest potential to learn how to live off-planet and exploit space resources to create routine access in cislunar space and into the Solar System.
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Repost, earlier post did not appear. Hyperlinks removed, titles of articles are still there.
Here’s a wild idea for the use of lunar resources. It may have no merit, but I found it interesting and would like to hear if any of it makes sense.
It seems that most of the elements present on the moon, not just volatiles implanted by the solar wind, may be used as part of various propellants, though not necessarily in the correct proportions and not without external hydrogen. Use of advanced and unconventional propellant combinations may lead to much more benefit from lunar ISRU and maybe even more efficient ISRU itself.
Two combinations are of particular interest:
- Silane + H2O2
Higher silanes + H2O2 are expected to be a dense, space storable and hypergolic propellant combination with better Isp and lower toxicity than MMH/NTO. This is useful for science missions, but since both silicon and oxygen are plentiful on the moon, this propellant combination would also benefit substantially more from lunar ISRU.
Prediction of Performance of (Higher) Silanes in Rocket / Scramjet Engines.
- MMH/Al/NTO gels
Under the ISTP project NASA is developing an advanced MMH/NTO engine called AMBR for science missions. The goal is to increase the Isp to about 375s in the next ten years or so. One of the more advanced techniques under consideration is use of gelled propellants, with significant amounts of metal powders combined with the MMH. Depending on the mass fraction of the metal, Isp and density can be increased.
AMBR* Engine for Science Missions
Again, a second effect is that a larger mass fraction of the fuel can be sourced from ISRU. MMH consists entirely of elements that are rare on the moon, whereas aluminium is plentiful. Mass fractions of up to 70% metal are a serious possibility. For high metal fractions, the Isp drops but this is likely more than compensated for by the increased potential for ISRU.
Preliminary Assessment of Using Gelled and Hybrid Propellant Propulsion for VTOL/SSTO Launch Systems
Theoretical Effects of Aluminum Gel Propellant Secondary Atomization on Rocket Engine Performance
The following article gives the average composition of the lunar regolith:
The average chemical composition of the lunar surface
The main elements are oxygen, silicon, aluminium and various other metals. Oxygen is of course an oxidiser. Silicon can be turned into silane if external hydrogen is provided or it can be used in powder form as an additive to a gel propellant. Aluminium and the other metals can similarly be used as metal-loading for gel propellants.
It looks as if nearly all of it could be turned into propellant, provided external hydrogen is supplied. This may seem no improvement over simply using hydrogen from Earth together with lunar oxygen, but it does mean that all of the regolith/ore could be processed into propellant, producing no slag. If the Isp of the resulting propellant is good enough, it may allow processing of the regolith to be moved to L1 instead of having to do it on the lunar surface.
Establishing the initial infrastructure there is cheaper than doing it on the lunar surface, because of the lower delta-v. Also, with uninterrupted sunlight and cheaper solar panels it would be much easier to generate massive amounts of power. You would still need some propellant production on the surface, but the scale could be reduced. This would work especially well for an architecture that wants to go to L1 anyway.
Comment by Martijn Meijering — June 1, 2009 @ 9:21 pm
Dr. Spudis,
Thank you for sharing your thoughts on this blog. Your ability to state the importance of exploring the moon in the 21st century may be unmatched. I hope you have an opportunity to testify before the Augustine Commission.
Jason
Comment by Jason — June 2, 2009 @ 12:40 pm
“the Moon is resource different”
Absolutely! ‘Skimming’ the regolith (think way big robotic combine harvesters) will also be a useful way of getting Helium too, as this is a non renewable. On the Earth
http://www.energybulletin.net/node/34563 “Peak Helium”. And this may be a viable industry after we are mining NEOs and other cometary debris for CHON. However equating “Unobtanium” to He 3 is a moondoggle too far, as we are far from the technological readiness of MkI Fusion let alone MkII. But is a useful pretext for a film!
A speculative left brain thought: could our regolith fields be ’seeded’ with materials designed to retain the wind blown volatiles and make the process more efficient? Or would skimming fresh ground be more productive? A useful near term experiment would be to discover how quickly an area is replenished. And a wild right brain dream: if we are going to create big furrows in Tranquility, why not draw a picture! Mega graphics! Something big enough to see with a telescope but not the naked eye would seem to be appropriate! Note “E=MC^2″ has only two curves:)
/speculation
Finally I echo Jason hopes. The commission needs the testimony of someone who has quietly but passionately advocated a return to the Moon over (too) many years!
Fingers Crossed!
Dave
Comment by Vacuum.Head — June 4, 2009 @ 5:47 am
[...] Last time, I outlined some of the basic principles of lunar resource utilization. The Moon is our nearest source of material resources in space and learning how to extract what we need from the Moon is a key skill in our expansion into the Solar System. [...]
Pingback by Lunar Resources – Part 2: Changing our approach to spaceflight | The Once and Future Moon — June 5, 2009 @ 6:04 am