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Collapse breccia near a lava tube entrance (Photo by Dr. Harmon Maher, Univ. Nebraska)

The science team of the Japanese Kaguya mission have just published a paper claiming to have found an opening to a cave on the Moon.  Such a discovery is a potentially important development for future lunar habitation.  Lava tubes are large caves created during the volcanic eruption of a very fluid, highly effusive lava.  They are common on Earth, especially in iron-rich basaltic lavas, such as those that make up most of the Hawaiian islands.

The idea that caves occur on the Moon has been around for a long time.  We have long known that the lunar maria (the dark, smooth, relatively uncratered plains of the Moon) are made up of old basaltic lava flows.  Looking at orbital photographs, we find many narrow, winding channels (or rilles) in the maria.  These channels cannot be the product of water erosion, as flowing liquid water cannot exist in the vacuum of the lunar surface.  So workers looked for another explanation.  They found it in lava channels and tubes.

On Earth, volcanic terrains often show small channels within young lava flows.  Lava tubes form when hot lava erupts, pouring out onto the surface.  The lava immediately begins to cool, with the outermost edges cooling first.  As the lava cools and hardens from the outside edges inward, the flow of still-molten lava becomes constricted to a central, narrow, interior conduit.  When the eruption stops, the still-liquid lava drains out, leaving behind an empty cave-like tube-shaped segment.  In some instances, the roof of the drained tube collapses, exposing the tube interior as a channel or, if less extensive, creating a “skylight” or a hole that allows access to the cave interior.  Lava caves are quite common on volcanoes made up of runny (low viscosity) lava, such as the shield volcanoes of Hawaii.

Caves found on the Moon would be very useful.  Because they form in dense basaltic lava, the space inside a tube is protected from both the hard radiation of the lunar surface and the constant micrometeorite bombardment the Moon experiences.  Moreover, the temperature of the subsurface of the Moon is very stable; below the zone which experiences the extreme temperatures of night and day, lunar temperatures are fairly constant at about -20° C.  On Earth, lava caves can be quite roomy, with diameters tens of meters across and hundreds of meters long.  On the Moon, these dimensions may be much larger – the low gravity of the Moon results in much bigger lunar lava tubes and channels than their terrestrial counterparts, being hundreds of meters across and many kilometers long.  Thus, they offer many potential advantages to future lunar inhabitants.

Before we pack our bags for the Marius Hills, we should take note of some other properties of lava tubes.  Many lava tubes partly or completely collapse immediately after their formation.  If the roofed segments are weakened by flowing lava, earthquakes, or are very thin, they cannot support their own weight and after the lava drains out, the roof falls into the void.  This is seen on both the Earth and Moon.  Hadley Rille, visited by the Apollo 15 astronauts in 1971, is a lava channel, parts of which were roofed over as a tube.  The crew landed near a channel portion, but a roofed segment is only about 12 km from the site.  High resolution images of that segment show no entrance to an underground cave there or elsewhere along the rille (channel).  That doesn’t mean that there is no cave portion of Hadley Rille, but it does suggest there is no entrance to a cave there.

Other candidates on the Moon look more promising.  Numerous lava tube “skylights” have been noted in association with many lava channels on the Moon.  These skylights are typically unconnected to each other or any nearby feature and are found as individual tube segments that appear to start and stop along the trend of a rille.  It is impossible to identify lava cave entrances because most of the images we have for these features are low resolution and have near-vertical viewing geometry.

The new Kaguya pictures show a circular, rimless pit on the floor of the projected segment of a rille.  Collapse pits are not uncommon on the Moon and many of them are not associated with lava channels or tubes.  So while the new Kaguya images are intriguing, they are not definitive evidence for a cave.

There are other issues in regard to the use of lunar lava tubes.  Many (if not most) terrestrial lava tubes are not void; they are either filled with late-stage lava, which plugs up the cave, or by collapse debris, which buries it.  Finding a new void lava tube is celebrated by the caving community simply because void tubes are rare.  But even if a void tube formed on the Moon, it may not remain that way for all time.  Lunar volcanism was active over 3 billion years ago.  Since then the Moon has been constantly bombarded by debris, initiating landslides, infilling craters, and generating seismic waves.  Such a bombardment could well act as a leveler to collapse and fill in void lava caves that might have existed on the Moon.

But the biggest problem with lunar caves is even more fundamental – they aren’t where we want them.  Sustained human presence on the Moon is enabled by the presence of the material and energy resources needed to support human life and operations around the Moon.  After over a decade of study and exploration, we now know that these locations are near the poles of the Moon.  Unfortunately, both poles are in the highlands and finding a lava tube in such non-volcanic terrain is highly unlikely, regardless of the imaginative ramblings of certain science-fiction authors.  If a lunar cave were present there, we would certainly consider using it.  But it makes no more sense to locate a lunar base near the caves, than it does to build a water-park in the Sahara desert.

The formation of lunar lava tubes and caves is an interesting scientific topic, but their utilitarian value is uncertain, at least until we have established a permanent presence on the Moon.  Ultimately, we may be able to use them to live on the Moon, but first, we need to follow the Willie Sutton principle and go where the money is.

New report - same old assumptions?

There is nothing more difficult to take in hand, more perilous to conduct, or more uncertain in its success, than to take the lead in the introduction of a new order of things. – Niccolo Machiavelli, The Prince.

In his famous book The Structure of Scientific Revolutions, Thomas Kuhn described two types of science: normal science, the everyday background work, where constant, steady but unspectacular advances occur in our knowledge, and revolutionary science, where fundamental assumptions and ways of conducting business are unalterably changed forever.  Kuhn called such a change a paradigm shift; a new paradigm (i.e., a framework of knowledge, including the assumptions, worldview, approaches and techniques to conduct business under a given set of circumstances) replaces the existing one and the new approaches and attitudes become the norm.

The paradigm model might also be applied to conducting business in other fields, in particular, the business of spaceflight.  Since it arose more than 50 years ago, the paradigm of spaceflight has largely remained unchanged.  In short, we conceive a mission (robotic or human), then design, build and launch a spacecraft to conduct that mission.  This satellite or spacecraft operates for a time in space—gathering information or providing a service—until it breaks down or becomes obsolete and is abandoned.  We then imagine the next mission—going back to the drawing board to design the next spacecraft—a process repeated continuously and a major cost of space exploration.

Is a paradigm shift – a “revolution” in space travel possible?  One would think that with 50 years of experience under our belts, we would have already exhausted all the possibilities.  Indeed, the imminent development of warp drive or “Cavorite” does not seem likely, but then, that’s the nature of truly revolutionary breakthroughs, isn’t it?  On the other hand, is there something missing – something that could be done right now using existing knowledge to change the rules of spaceflight and possibly spur additional breakthroughs?

As long as we’re chained to the existing spaceflight paradigm, we must continue hauling from Earth everything we need in space.  For human missions this includes all the air, water and other consumables needed for life support.  The cost to lift all this mass (which includes the weight of a massive amount of fuel needed to escape from Earth’s very deep gravity well) is budget busting.  So for “normal” space exploration, costs will never be lower except at the margins and we will always be mass-limited in space.  And when you are mass-limited, you are capability-limited as well.

I’ve argued here and elsewhere that there is a method that is already well understood in principle, but its practical application and viability is completely unknown.  If we could use what we find in space to create new capabilities, we would change the rules of spaceflight, thereby ushering in a true paradigm shift in space travel.

Such was the original intent of the Vision for Space Exploration (VSE).  The desire for fundamental change in perspective was behind the program’s specific direction to study and experiment with using the material and energy resources of the Moon.  From the moment it was announced, the true purpose of a lunar return was misunderstood, both inadvertently and deliberately.  Constellation is a rocket program; the VSE is not.

No one knows if using space resources is possible but we can find out by pursuing innovative technology.  In theory it works.  We’ve never attempted high-risk mining on the Moon and it may have significant practical difficulties but potentially, it could become a highly leveraging activity.

If we can extract and make rocket propellant on the Moon, we can create a completely reusable, refuelable transportation infrastructure in cislunar space.  If we can extract the oxygen and hydrogen, we can live in space.  Of course, such an outcome would change and transform the business model of space—something that fascinates and attracts many but repels others and hence, its mixed reception in aerospace circles.

This would truly be a revolution, a paradigm shift in the same sense as we understand it from Kuhn’s description of scientific progress; as a vast new expanse is opened to us and we are free to move about the universe, the world changes and things are never the same again.

In order to mitigate risk and to ensuring our economic and national security, government often steps in to develop technology that the private sector cannot or will not take on.  A government push to learn how to use the resources of space will break the cycle of launch and discard.  Instead of having a short “shelf-life,” our indispensable and unprotected systems in space become maintainable, reusable, extensible and affordable.

While reading the newly released Augustine report, keep in mind its background and its assumptions.  It is based solidly on the traditional models of conducting business in space – design, launch and abandon, along with the accompanying plea for more money to ensure a “robust” program of space exploration.

As long as such assumptions prevail, advances never will.

The LCROSS impact site seen from LRO

Early last Friday, the public and families of employees at Ames Research Center in California, where the LCROSS mission was conceived, built and operated, camped on the lawn in an all-night vigil.  NASA’s educational outreach and public relations push about the pending lunar impact event was very effective, having reached a wide audience in the weeks leading up to the much hyped event.  Alas, the promised giant plume of impact debris was invisible from Earth, leaving a receptive public feeling cheated and disappointed.

The understanding that a high-velocity impactor can yield important information about planetary composition and state is very old.  The first probes to the Moon (both Soviet and American) were impactors.  We know that when something strikes a planetary surface at high speed, target material is thrown up into space, some of it vaporized by heat generated in the energy of the impact.  By studying this impact ejecta, we learn about the composition of the target object.

I didn’t post on it earlier, but as the LCROSS mission has successfully concluded, I think it is a good time to examine this mission, how it came about, and the lessons that hopefully it has taught NASA about public appeal and its involvement with space.

LCROSS was not originally a part of the robotic precursor program for lunar return. Initially, the Lunar Reconnaissance Orbiter (LRO) spacecraft was to be launched on a Delta II.  By the end of 2005 it had outgrown its booster and was forced onto the much larger Atlas V booster where it had surplus payload margin.  The Associate Administrator for the Exploration Systems Mission Directorate (ESMD) Scott Horowitz, decided to use this margin to fly an additional small spacecraft (called a secondary payload) that would address the raging debate about whether water ice exists at the poles of the Moon.  Horowitz looked to NASA’s field centers for a small payload that would provide data about this contentious and nagging issue.

Although a variety of small missions were proposed, including survivable hard landers and small “hoppers,” the idea of slamming the Centaur upper stage into the Moon and examining the resulting ejecta plume was selected as LCROSS in April 2006.  It was considered a low-risk, low-cost concept, as the used Centaur upper stage had no value and would have been steered into a solar orbit anyway.  A small satellite was built to track the Centaur impact, measure the properties of the ejected plume and with luck, would “settle” the issue of water on the Moon.

A serious defect in this mission concept was that it presupposed that we understood the Moon well enough to identify in advance the most likely site for ice on the Moon.  Lunar investigators knew from previous data that water ice, if present, was not present everywhere – it had a patchy, heterogeneous distribution because the permanent shadow around the poles (where the ice would be stable) is itself patchy.  Moreover, the remote sensing data of the time was ambiguous as to which shadowed locales contained ice, if any.

In March of 2006, because of these uncertainties, those who had worked on the robotic precursor program laid out a sequential, incremental strategy to first map the deposits from orbit and identify the best candidate sites for ice.  Following orbital mapping, we would soft-land with capable rovers and  map and test the surface composition at a minimum of about 20 different sites.  Although this strategy is more costly than a simple impactor mission, it would have provided us an unequivocal answer to the ice issue; we would know without doubt whether there is or is not water ice at the poles of the Moon.  Moreover, rovers would collect information on the possible presence, physical nature and setting of other volatile substances (such as ammonia and methane) that have resource value.  In other words, we would have collected the critical strategic information needed to locate, prospect, harvest and use lunar water.

Instead, the mission chosen and flown and heavily advertised by NASA as a citizen participation viewing event to find water on the Moon, could not answer key questions about polar water.  If LCROSS detects water, we still won’t know where all the ice deposits are located, what other species might be present, what its physical state might be, and how it is distributed laterally and vertically in the surface regolith.  If LCROSS detects nothing, it won’t prove that water doesn’t exist on the Moon, only that the wrong site was selected.  In other words, after this mission, we will still know next to nothing about the material that will enable and advance permanent, sustainable economic presence on the Moon.

An impact plume wasn’t the only thing missing.  Hopefully, NASA will recognize the real discovery of LCROSS – mission hype is a poor substitute for shortcomings in programmatic logic.

A cislunar transport system will revolutionize space travel (NASA artwork by Pat Rawlings)

Water is an extremely useful substance in space.  The recent finding of water on the Moon has generated considerable comment in the space community; a quick search on Google using the phrase “lunar water” returns over 7.66 million hits.  Lunar water’s significance lies not in its role as a medium for the presence of extraterrestrial life but rather in its potential to support terrestrial life—ours—as humanity moves beyond Earth.  The Moon is the port from where we will navigate—the safe harbor where we will learn how to live and work productively in space and from where we will set sail into our Solar System, thereby ensuring the survival of our species.

The three principal uses for this water are life support, energy storage, and rocket propellant.

We can easily imagine drinking water.  We need about 2 liters of water per day under ordinary circumstances.  Water is also a constituent of food, both unprepared and preserved, adding at least another liter to that total.  In addition to consumed water, we can also use water to make oxygen, replenishing the air we bring with us to create a breathable atmosphere.  Water is over 85% oxygen by weight and the liquid is easily broken into its constituent gases by passing an electrical current through it.

Another way that water supports life is by offering shielding and protection against solar and galactic cosmic radiation.  Water harvested from the Moon can fill the outer jackets of surface habitats, protecting not only human life and technology within it, but also the plants that we will want to grow there, both for food supply and carbon dioxide scrubbing of the habitat air.  Thus, water supports life on the Moon as both a consumable and as a building material.

A second main use of water is less often considered.  We can break down water into its component gases using electricity, but the process can also be reversed – hydrogen and oxygen gas can be combined to generate electricity in a device called a fuel cell.  When these gases combine, they generate electrical energy and make water as a by-product.  This technique was used in the Apollo spacecraft for power and water production.  When combined with another technique to generate electrical power (e.g., arrays of solar cells or a nuclear reactor), we make a completely reversible, self-sustaining power and water system.  Thus, the water becomes a medium of energy storage – during lunar night, we combine hydrogen and oxygen to make water and electrical power while during the daytime, we reverse the process by using electrical power generated by sunlight to disassociate the water back into its constituent gases.  Such a rechargeable fuel cell system enables permanent, sustainable human presence on the Moon.

The third important use for lunar water is for the production of rocket fuel.  Liquid hydrogen and oxygen are the most powerful chemical rocket propellants known.  By manufacturing rocket propellant from lunar water, we make the Moon a refueling station and logistics depot in space.  The critical value of this ability is that such rocket fuel not only permits our routine access to and from the Moon, but also enables access to any other point in cislunar space (the volume of space between Earth and Moon.)

All satellites reside in cislunar space.  Numerous remote-sensing satellites are found in low Earth orbit.  GPS elements reside in moderately high (few hundred kilometer) orbits.  Communication satellites are found at geosynchronous orbit, 35,000 km above the Earth.  Other specialized satellites occur at different altitudes.  At present, we cannot access these satellites with either human or robotic spacecraft.  So we design, build and fly these space assets, use them for a time then abandon them, replacing them as needed with new satellites—at great cost.  The ability to reach valuable space assets routinely with people and machines allows us to change the way we conduct business in space.  Instead of the current “fly and throw away” template, we can build extensible, maintainable and upgradeable systems.

Very large, distributed space systems will enable new capabilities, such as global communications using hand held cell phone-sized equipment, anywhere in the world at any time.  New remote-sensing platforms can be built to look at any corner of the globe at any wavelength in unprecedented detail.  Telescopes built on the Moon’s far side, where they will be shielded from Earth’s radio noise, can scan the universe in new areas of the spectrum. These and many more capabilities are enabled by a cislunar transportation system and will vastly improve life on Earth.

By understanding and using the resources of our Moon, we can push out to the stars.  An abundance of water on the Moon fundamentally allows us to change the rules of exploration and spaceflight to our advantage.  We stand at the threshold of a new understanding of how the Moon evolved and works—and works to humanity’s advantage.