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The Moon: Useful and on the way

By abandoning the Moon, the administration’s proposed space policy has left the space community with a huge question mark over the important issue of learning how to harvest and use space resources.  Clearly if we don’t go to the Moon with people or machines, there is no way to use the abundant water, metals, and other lunar surface materials to create new capabilities in space.  Supporters of the new path suggest instead that we can obtain all the materials we want from near-Earth asteroids, small, rock-like objects that co-orbit the Sun with the Earth.  Indeed, some asteroid types appear to contain significant quantities of water, thus offering a possibly rich source of off-planet water.

Water is an extremely useful substance in space.  By virtue of its varied utility, water enables extended human presence in space.  Besides its obvious role as a sustaining substance for human life (both drinking and providing oxygen for breathing), water is also an excellent material to shield from cosmic radiation and a medium of energy storage, both by thermal storage and also through its use in rechargeable fuel cells, where hydrogen and oxygen are combined at night (producing water and electricity).  Stored water is disassociated by solar generated electricity during the day and re-stored as hydrogen and oxygen.  Most importantly, water can be converted into liquid hydrogen and liquid oxygen; in this form, it is the most powerful chemical rocket propellant known.

So what are the relative benefits and drawbacks of using asteroidal (not lunar) resources?  The biggest advantage of asteroids is that they have extremely low surface gravity.  As these objects are simply very large rocks, they don’t have much mass and hence, virtually no surface gravity.  A mission to an asteroid is more akin to a rendezvous in space than it is to a planetary landing.  The advantage this confers is that vehicles can come and go to a given asteroid without the requirement to expend large amounts of propellant in a landing, with total changes in velocity measured in the few meters to tens of meters per second range.  In contrast, a landing on the Moon requires a propulsive burn of over 2200 meters per second, both coming and going.  This deep “gravity well” penalty is much smaller than launching from Earth (11,000 meters per second), but is still substantial compared with “dimple” dimensions of asteroid gravity wells.

If the propulsive energy of access were the only (or even the main) consideration for resource exploitation, asteroids would win hands down.  But there are some other issues to consider.  Water is indeed present in the materials of Near-Earth asteroids, but in a chemically bound form.  Water molecules fill sites in the crystal structures in rock-forming minerals, bound strongly to its encasing structure.  These chemical bonds must be broken to extract the water and that takes energy.  On the Moon, water occurs in bound form, but also in its native state as ice in the lunar polar regions.  Ice-laden dirt can be scooped up and minimally heated to extract the water.  In contrast, it takes 100 to 1000 times more energy to extract a kilogram of water from chemically bound asteroidal minerals than it does to scoop up the “free water” found in the lunar cold traps.  The greater quantity of energy needed to extract water from an asteroid is annoying, but can be handled through the use of large solar arrays or even a nuclear reactor to generate copious amounts of electrical power.  But both solutions bring significant mass penalties and a nuclear reactor significantly increases cost, both from the technical development it would require and from the hurdles raised by legal and environmental groups it would have to overcome.

A more critical issue is the location of the two resource bodies.  The proximity of the Moon is a major boon for its utilization.  The Moon is both close and accessible.  In terms of closeness, it takes 3 seconds for a radio signal traveling at the speed of light to go the Moon and back.  This makes the remote, telepresence operation of lunar robots from Earth feasible.  Early steps in the location, surveying and harvesting of demonstration amounts of resources on the Moon can be done remotely with robots controlled from Earth.  We do not have this luxury with asteroids.

Asteroids orbit the Sun (like the Earth does) and vary in distance from Earth by tens of millions of miles over the course of a year.  At best, asteroids are several tens of light-seconds away and at times, tens of light-minutes.  This long radio time-lag means that direct remote operation of robots on asteroids will be cumbersome, if not impossible.  For well understood routine tasks, this may not be a serious issue, but space resource utilization is something we have yet to learn.  It is unclear whether we will be able to harvest and process asteroid water using remote robots, but it is almost certainly possible to do so with robots on the Moon.

The other aspect of the Moon’s proximity is accessibility, the ability to access a space destination routinely and often.  As the Moon orbits the Earth, we can go to and come back from the Moon pretty much at will – launch windows are almost always open.  In contrast, because even near-Earth asteroids follow their own paths around the Sun, launch windows are short and come at irregular (albeit predictable) intervals.  Round trips to and from asteroids are even more difficult and after multiple weeks to months of travel, loiter times are either very short (on the order of a week or so) or very long (a year or more).  This wildly variable duration of access may be handled on a robotic mission, but it precludes any significant human/robot interaction during the materials processing on an asteroid.

Finally, there is the issue of surface gravity.  Much of the “dirty work” of resource processing involves separating some substance from another, or extracting something embedded.  Having gravity usually makes this an almost trivial step, one that we don’t think about very much – unless we don’t have it.  The Moon does indeed have a significant gravity well (about 1/6 that of the Earth) and although this works against us when we want to export product, it works in our favor when we need to process materials.  The extremely weak surface gravity of an asteroid is almost microgravity and makes it very difficult to separate materials there without specialized equipment, again adding mass, power, complexity and cost to the processing chain.

In short, there are many considerations to take into account when planning an architecture based on resource exploitation.  The seemingly damning case against going to the Moon to harvest material resources largely revolves around its relatively high surface gravity.  It takes roughly two tons of water-equivalent liquid hydrogen-liquid oxygen propellant to lift one ton of water to the L1 point, where it can be used to supply and fuel a variety of spacecraft destined for many different places.  That same ton of water lifted from the Earth would take over 19 tons of propellant to deliver it.  The other side of that coin is that gravity is extremely useful – if not critical – for many materials processing techniques.  Gravity can only be artificially created near an asteroid at some expense and mission complexity, whereas on the Moon, it’s a feature that comes for free.

Learning how to access and use space resources is a critical skill for a space faring society – skills and knowledge that will reap rewards right here on Earth.  The Moon offers us a school and a laboratory for acquiring this critical knowledge.  By virtue of its proximity, accessibility and resource endowments, the Moon satisfies our early space ISRU needs and allows us to create new capabilities to routinely access cislunar space, where all of our economic and national security space assets reside.  The asteroids have much to offer for material resources and we will eventually journey to and use many of them.  But we have business on the Moon first.  Mining the unlimited wealth of the Solar System will become inevitable once we have learned the lessons of how to do this job on our nearest neighbor.

O Fortuna! Irony intentional?

During a recent interview on Al Jazeera television, NASA Administrator Charles Bolden outlined NASA’s new priorities.  His remarks became headlines as the previously ignored story about the redirection of the space agency toward international diplomatic outreach and global climate change research finally reached the many who still hold NASA in high regard.  Beyond the inane and vacuous policy comments, one statement by Administrator Bolden went virtually unnoticed: “We’re not going to go anywhere beyond low Earth orbit as a single entity,” he revealed, “The United States can’t do it.”  If it’s possible to shock Americans into paying attention to NASA and our national space program, those words might do it.

It’s one thing to assert that the Unites States desires more international collaboration as a matter of policy for reasons of fostering alliances, developing new cultural ties, or even to promote world peace.  It’s an entirely different proposition to assert that the United States has lost the ability to reach for the stars, that America is incapable of exploring space alone.  Have we become comfortable with the idea that it’s politically incorrect to have pride in our nation’s abilities – past, present and future?

The natural reaction of many Americans is to strongly protest such a notion by asserting that our technology is the greatest in the world and that we can design and build anything we choose to.   However, one can not escape the reality that the statement quoted above was made by the head of the agency charged with sending U.S. astronauts into space, a task that Americans have watched NASA carry out for almost 50 years.  A more troubling thought is that maybe he is right.

I’ve worked with NASA for 25 years on experiments, research, and advanced planning and missions.  I’ve been involved with studies to put a base on the Moon since 1984 (the year of the first conference on lunar bases at the National Academy of Sciences in Washington DC).  In all of these efforts, I believed that our future in space was at stake and that we were preparing for humanity’s return to the Moon, followed by journeys to the planets.

As the years wore on, it began to dawn on some of us that some within and outside the agency really didn’t want to go anywhere or do anything in space.  Working for NASA means being involved in the process of working.  How you structure a project, who gets assigned what work and how many meetings you conduct is the formula that elevates you faster than when (or even if) you deliver a product, a mission or a program.  This culture becomes even more evident as one ascends the chain of command.  The farther up the organizational ladder you go, the further removed from the productive segment of the agency you are, with product being replaced by an ever multiplying and bewildering variety of workshops, seminars and management training retreats.  There exists in America today a thriving industry dedicated to convincing people who have no organizational or management skills that in fact, they are all excellent organizers and managers.  Much of this sub-culture is accurately (and hilariously) portrayed in the comic strip Dilbert.

Management fads like Total Quality Management regularly come and go.  NASA has dabbled in Faster-Cheaper-Better, Spiral Development, Earned Value Management, and many others.  Each new initiative is unveiled as The Answer, the magic beans solution that will re-establish the NASA of our forefathers – smart, productive, innovative, and competent.  Management thrives by producing more middle managers.  People joke about highway projects where one guy digs a hole while five others lean on their shovels, watching him work.  That old chestnut always gets a laugh because we’ve all seen it at some point.  You see it a lot within NASA.  As administrative cost consumes more and more of the budget pie, the slice that represents funding for the productive sector of the agency keeps shrinking.

Bolden’s comment is tragic, not in its misunderstanding but in its verity.  America cannot go back to the Moon by itself not because we lack the wealth or the technical skills but because we have developed a culture of management bloat and process-orientation that proliferates bureaucracy.  NASA is comfortably cushioned from the reality of their organizational maladies by the amazing legacy inherited from those who did great things in the past.  They may believe they’re immune to the Cult of Management, but as evidenced by Bolden’s statements, the agency has changed.  NASA has become a “feel-good” bureaucracy, stuck on the idea of doing one-off stunts in space for public approval and a guaranteed institutional lifetime, paid for by the public.  This attitude both inside and outside of the agency has lead to the demise of our national spaceflight capabilities.  Stagnant entities reflexively dwell on past glory; dynamic ones build upon them to create something both significant and permanent.

Occasionally, I’m asked why I stay in the space business.  I do so because I believe in the mission of space exploration and in the importance of moving humanity into the Solar System.  Every now and then, an opportunity arises outside the boundaries of normal business to do something productive and create a lasting legacy – a time when the stars align and a leader refuses to follow the established rules or to unimaginatively subscribe to the conventional wisdom.

Currently, the “right stuff” manifests itself as a pattern of waiting for a propitious political opportunity and a few far-seeing people to seize the day and push through something that otherwise would be buried by “process.”  In my opinion, the Vision for Space Exploration was such an opportunity – a path forward, achievable in stages, that would have created a legacy of space faring capability.  The idea of actually doing something made the Vision a nonstarter to many within the agency – it challenged their worldview of process over product.  They are content to merely manage an organization.  The goal of leading America and the world into the Solar System has become a slogan in a strategic plan, an ever-fading banner over an office door.

Is any of this fixable?  Perhaps.  For now, the opportunity to strengthen the U.S. space program, an endeavor that has traditionally pushed technology development and stoked our economic engine, has been kicked aside.  But by their very nature, new opportunities arise unbidden and unforeseen at irregular intervals.  I wonder if we’ll do better next time.

Americans need to wonder.

Red symbols on this map of lunar crustal thickness show where the Kaguya team have identified deposits of olivine

We’ve studied and examined the Apollo samples of the lunar maria (pronounced MAR-ee-uh) for thirty years but despite the thorough search of these collections, we have never found a sample of the deep mantle from which these lavas were formed.  How might such a deeply seated rock find its way to the surface?  Large basin-creating impacts on the Moon might have dug through tens of kilometers of crust (down into its deepest layers) to excavate samples of the mantle.  Another occurrence of mantle samples is as small chunks of rock included in lava.  Fragments of rock may be ripped away during the ascent of the dense, liquid magma and become inclusions in the solidified lava flows; these “stranger” rocks are called xenoliths.  Despite an exhaustive search of the Apollo samples, no samples of the mantle have been found, either as a fragment of basin ejecta or as a xenolith in the mare basalts.

If no one has ever seen it, how do we know what the lunar mantle looks like?  The properties and composition of planetary interiors are inferred by indirect evidence.  Seismometers left on the surface by Apollo crews measured the velocity of seismic waves inside the Moon, an indirect measure of the density of the deep interior.  The density of the mantle is high enough so that common surface rocks cannot make up a significant portion of it; the rocks must contain large amounts of the minerals olivine and pyroxene.  In addition, the mantle rocks were partially melted to make the mare basalts that cover the surface in places.  The chemical composition of these lavas show they were made by melting a rock rich in magnesium and iron.  Finally, xenoliths of the Earth’s mantle are sometimes found entrained in lavas – these pieces are made up of the olivine-pyroxene rock peridotite (after the mineral olivine (the gem form is peridot) that makes up most of it.)  So the idea that the rocks of the mantle are olivine-rich is a well-grounded concept for which we have abundant independent evidence.

Now a new scientific paper concludes that fragments of the mantle (the dense magnesium- and iron-rich portion of the Moon that lies below 70-100 km depth) are exposed on the surface, brought up from depth by the impact of giant asteroids 4 billion years ago.  Such a finding would indeed be significant, as geologists always seek rocks from the deep interior to aid our understanding of the Moon’s structure and composition.  Data from the orbiting Japanese Kaguya mission shows that olivine is present in the surface deposits of some lunar craters.  But how do they go from this observation to the interpretation of lunar mantle?  Basically, they mapped out the occurrences of these olivine deposits and found that many of them occur within the rims of large impact basins.  Based on models produced from gravity mapping, the crust of the Moon is thought to be thin here and the mantle is close to the surface.  Thus, these large impact basins could have excavated chunks of the mantle, throwing them out onto the surface of the Moon.

Why is the mineral olivine important?  Olivine is a silicate mineral rich in magnesium and iron; it forms one of the basic, silicate building blocks of the rocky planets.  In magma (liquid rock), olivine crystallizes first and its composition is a key indicator of the composition of the magma.  Current prevailing wisdom is that the early Moon was largely molten (the “magma ocean” phase); whether it was completely molten or merely liquid in its outer portion is uncertain, but in such a huge system of liquid rock, olivine is the earliest mineral that crystallizes.  Being dense, crystallizing olivine would sink in the liquid magma, slowly accumulating deep in the Moon.  As the entire Moon solidified, these “cumulate” layers of olivine and other iron-rich minerals would make up the mantle.  Later, the mantle partially re-melted, creating liquids that erupted onto the surface as basalt lava and formed the dark lowland plains – the maria.

So how does the Kaguya interpretation hold up on examination?  Estimates of crustal thickness are of the current Moon, after the basins formed.  There is no particular reason to suppose that a given basin-forming impact occurred in terrain of thin crust – the crust is thin here because the basin formed.  True enough, some of these impact features are very large – the Imbrium basin, a large crater on the western near side, is well over 1000 km in diameter, large enough to have punched through the thickest sections of the crust, one would think.  Indeed, Imbrium is one of the sites that the Kaguya team propose as having excavated mantle.  So they are finding these areas in the places where one might expect to find them.

Olivine is a very common mineral and abundant in the lunar crust.  A curious fact is that olivine grains in lunar highland rocks tend to have high amounts of calcium, a minor element but a key diagnostic of the crystallization environment.  In Earth rocks, olivine formed at depth has very low concentrations of calcium.  My colleague, the late Graham Ryder concluded that the olivine crystals in dunite (a rock made up almost completely of olivine) from the Apollo 17 site – a sample proposed as a piece of the lunar mantle – likely came from the accumulation of crystals at a depth of only a few kilometers, far shallower than the tens of kilometers depth to the mantle.

Because the Kaguya spectral mapper is detecting only the presence of olivine, we cannot distinguish between pure olivine and olivine crystallized with plagioclase, what lunar scientists call troctolite.  Troctolite is common in the Apollo highland samples, but is a relatively rare rock on Earth.  It consists of (more or less) equal parts olivine and plagioclase, a calcium- and sodium-rich silicate mineral.  Troctolites make up some of the most deeply derived rocks found in the Apollo collections, but all studied to date seem to be of crustal, not mantle, provenance.  There is no objective evidence that the olivine seen by Kaguya is not derived from troctolites and/or dunites of crustal (not mantle) origin.

The long held desire of lunar scientists to sample deeper levels of the Moon is understandable, but we must proceed cautiously.  Just as a sample return mission to the floor of the largest basin on the Moon is no guarantee that we will obtain the rocks needed to answer questions about early cratering history, the new finding of abundant olivine on the Moon does not mean that pieces of the mantle are lying on the surface, awaiting collection by some future mission.  The Kaguya findings are intriguing and very interesting, but not definitive evidence for the presence of mantle fragments on the lunar surface.