AirSpaceMag.com

The Great White Fleet of the United States Navy, 1907 -- We need a fleet of spacecraft to open "This New Ocean" of space

We seem to be in one of those periods in which basic reasons for doing what we do as a nation are called into question.  This includes our national civil space program, which for the last few years has engaged in an extended period of back-biting and navel-gazing.  Much of this “debate” has focused on either or both of two points: what rocket to build and where to go, and not on sustainability.

In an era of limited resources, our challenge is to create a worthwhile space program with an expenditure rate that falls at or below a level perceived as affordable.  Given this reality (regardless of prevailing agency direction or assertions about projected deep space destinations) it is highly likely that cislunar space will be the sphere of space operations for the coming decade or two. Thus the questions should be:  What are we doing in space and why are we doing it?  If the answer is a series of space exploration “firsts” (flags-and-footprints forever), that model will require specific activities and missions.  If the answer is that an incrementally developed transportation infrastructure is desired, one that creates an expanding sphere of human operations, then such a model requires a different set of specific activities and missions.

Thus, the real debate is not about launch vehicles or spacecraft or even destinations; it is about the long-term – the paradigm or template of space operations.  One model requires mega-rockets to distant targets for touch-and-go missions; for convenience, I’ll call it the “Apollo” template (no denigration intended).  The other model is an incremental, go-somewhere-to-stay-and-then-expand-onwards mindset – call it the “Shuttle” template (again, same disclaimer).  The one that you adopt and follow depends on what purpose you believe human spaceflight serves.

Because Mars may harbor former or existing life, NASA has presumed that it is our “ultimate destination” in space.  In effect, the entire focus of the human spaceflight effort has devolved into a huge science project – “The Quest for Life” (which means finding pond scum, not ET).  Thus, debate about what to build, where to go and how to do it must be formulated towards attainment of Mars.

This unspoken assumption has been at the root of most space objective studies for the past 20 years.  Mars was the end point of President George H.W. Bush’s Space Exploration Initiative, President George W. Bush’s Vision for Space Exploration, of former Lockheed-Martin President Norm Augustine’s two reports, and a myriad of space groups and societies.  From the 1990′s to the present, a multi-billion dollar robotic campaign has sent mission after mission to Mars, each discovering that the red planet once had liquid water.  This mania for Mars and preoccupation with possible life there, has blinkered our perceptions of the space program and distorted our reality of what is possible or attainable on reasonable time scales with available resources.

Long term, the goal for human spaceflight is to create the capability to go anywhere we choose, for as long as we need, and do whatever we want to in space.  For the sake of argument, if one accepts such a goal, which model is more amenable to implementing it: the Apollo template or the Shuttle template?

If our goal is to “sail on the ocean of space,” we need a navy.  Navies don’t operate with just one class of ship because one class isn’t capable of doing all that is necessary.  Not all ships will look or operate the same because they have different purposes and destinations.  We need transports, way stations, supply depots, and ports.  In space terms, these consist of one to get people to and from space (LEO), one to get them to and from points beyond LEO, way stations and outposts at GEO, L-1, low lunar orbit, and to the lunar surface.  To fuel and provision our space navy, we require supply (propellant) depots in LEO, L-1 and on the lunar surface.  Ports of call are all the places we may go to with this system.  Initially, those ports are satellites in various orbits which require service, maintenance and replacement with larger, distributed systems.  Later, our harbor will be the surface of the Moon, to harvest its resources, thereby creating more capability and provisions from space.  Reliable and frequent access to the entire Solar System, not one or two destinations, should be our ultimate goal.

By designing and building mission-specific vehicles and elements, the “Apollo” template forfeits going everywhere and doing everything.  However, adopting the “Shuttle” model does not preclude going to Mars.  In fact, I contend that to go to Mars in an affordable manner that sustains repeated trips, one needs the infrastructure provided by a space faring navy.  Building a series of one-off spacecraft – huge launch vehicles to dash to Mars for expensive, public relations extravaganzas will eventually put us right back in the box we’re in now.

We have been arguing about the wrong things.  It is the mindset of the space program that needs re-thinking – not the next destination, not the next launch vehicle, and not the next spacecraft.  How can we change the discussion?  First, we need to understand and articulate the true choices so that people can see and evaluate the different approaches and requirements.  Second, we need to develop sample architectures that fit the requirements for “affordable incrementalism.”  Finally, we need to get such plans in front of the decision makers.  There is no guarantee that they will accept it or even listen to the arguments for it.  But right now, they are completely ignorant about it.

A cost-effective, sustainable human spaceflight program must be incremental and cumulative.  Our space program must continually expand our reach, creating new capabilities over time.  Moreover, it should contribute to compelling national economic, scientific and security interests.  Building a lasting and reusable space transportation system does that, whereas a series of PR stunt missions will not.  The original vision of the Shuttle system was to incrementally move into the Solar System – first a Shuttle to-and-from LEO, then Station as a jumping off platform and then beyond LEO into cislunar space.  We have the parts from the now retired Shuttle system and an assembled and working International Space Station.  We can use these legacy pieces to build an affordable system to access the near regions and resources of cislunar space.  In this new age of austerity, perhaps we will finally acquire the means to build our pathway to the stars.

Setting up a mining operation on an asteroid may be difficult (from Howstuffworks.com)

Part III:  Resource Utilization Considerations

In Part I and Part II of this series, I examined some of the operational and scientific issues associated with a human mission to a near Earth asteroid (NEO) and contrasted them with the simpler operations and greater scientific return of a mission to the Moon.  To continue the discussion of what we might do at an asteroid, I will now consider using the local resources offered by asteroids, how they differ from those of the Moon, and offer some practical considerations on accessing and using them.

To become a truly space faring species, humanity must learn how to use what we find in space to survive and thrive.  Tied to the logistics chain of the Earth, we are now and always will be limited in space capability.  Our ultimate goal in space is to develop the capability to go anywhere at any time and conduct any mission we can imagine.  Such capability is unthinkable without being able to obtain provisions from resources found off-planet.  That means developing and using the resources of space to create new capabilities.

One of the alleged benefits of asteroid destinations is that they are rich in resource potential.  I would agree, putting the accent on the word “potential.”  Our best guide to the nature of these resources comes from the study of meteorites, which are derived from near Earth asteroids.  They have several compositions, the most common being the ordinary chondrite, which makes up about 85% of observed meteorite falls.  Ordinary chondrites are basically rocks, rich in the elements silicon, iron, magnesium, calcium and aluminum.  They contain abundant metal grains, composed mostly of iron and nickel, widely dispersed throughout the rock.

The resource potential of asteroids lies not in these objects, but in the minority of asteroids that have more exotic compositions.  Metal asteroids make up about 7% of the population and are composed of nearly pure iron-nickel metal, with some inclusions of rock-like material as a minor component.  Other siderophile (iron-loving) elements including platinum and gold make up trace portions of these bodies.  A metal asteroid is an extremely high-grade ore deposit and potentially could be worth billions of dollars if we were able to get these metals back to Earth, although one should be mindful of the possible catastrophic effects on existing precious metal markets – so much gold was produced during the 1849 California Gold Rush that the world market price of gold decreased by a factor of sixteen.

From the spaceflight perspective, water has the most value.  Another type of relatively rare asteroid is also a chondrite, but a special type that contains carbon and organic compounds as well as clays and other hydrated minerals.  These bodies contain significant amounts of water.  Water is one of the most useful substances in space – it supports human life (to drink, to use as radiation shielding, and to breath when cracked into its component hydrogen and oxygen), it can be used as a medium of energy storage (fuel cells) and it is the most powerful chemical rocket propellant known.  Finding and using a water-rich NEO would create a logistics depot of immense value.

A key advantage of asteroids for resources is a drawback as an operational environment – they have extremely low surface gravity.  Getting into and out of the Moon’s gravity well requires a change in velocity of about 2380 m/s (both ways); to do the same for a typical asteroid requires only a few meters per second.  This means that a payload launched from an asteroid rather than the Moon saves almost 5 km/s in delta-v, a substantial amount of energy.  So from the perspective of energy, the asteroids beat the Moon as a source of materials.

There are, however, some difficulties in mining and using asteroidal material as compared to lunar resources.  First is the nature of the feedstock or “ore.”  We have recently found that water at the poles of the Moon is not only present in enormous quantity (tens of billions of tons) but is also in a form that can be easily used – ice.  Ice can be converted into a liquid for further processing at minimal energy cost; if the icy regolith from the poles is heated to above 0° C, the ice will melt and water can be collected and stored.  The water in carbonaceous chondrites is chemically bound within mineral structures.  Significant amounts of energy are required to break these chemical bonds to free the water, at least 2-3 orders of magnitude more energy, depending on the specific mineral phase being processed.  So extracting water from an asteroid, present in quantities of a few percent to maybe a couple of tens of percent, requires significant energy; water-ice at the poles of the Moon is present in greater abundance (up to 100% in certain polar craters) and is already in an easy-to-process and use form.

The processing of natural materials to extract water has many detailed steps, from the acquisition of the feedstock to moving the material through the processing stream to collection and storage of the derived product.  At each stage, we typically separate one component from another; gravity serves this purpose in most industrial processing.  One difficulty in asteroid resource processing will be to either devise techniques that do not require gravity (including related phenomena, such as thermal convection) or to create an artificial gravity field to ensure that things move in the right directions.  Either approach complicates the resource extraction process.

The large distance from the Earth and poor accessibility of asteroids versus the Moon, works against resource extraction and processing.  Human visits to NEOs will be of short duration and because radio time-lags to asteroids are on the order of minutes, direct remote control of processing will not be possible.  Robotic systems for asteroid mining must be designed to have a large degree of autonomy.  This may become possible but presently we do not have enough information on the nature of asteroidal feedstock to either design or even envision the use of such robotic equipment.  Moreover, even if we did fully understand the nature of the deposit, mining and processing are highly interactive activities on Earth and will be so in space.  The slightest anomaly or miscalculation can cause the entire processing stream to break down and in remote operations, it will be difficult to diagnose and correct the problem and re-start it.

The accessibility issue also cuts against asteroidal resources.  We cannot go to a given asteroid at will; launch windows open for very short periods and are closed most of the time.  This affects not only our access to the asteroid but also shortens the time periods when we may depart the object to return our products to near-Earth space.  In contrast, we can go to and from the Moon at any time and its proximity means that nearly instantaneous remote control and response are possible.  The difficulties of remote control for asteroid activities have led some to suggest that we devise a way to “tow” the body into Earth orbit, where it may be disaggregated and processed at our leisure.  I shudder to think about being assigned to write the environmental impact (if you’ll pardon the expression) statement for that activity.

So where does that leave us in relation to space resource access and utilization?  Asteroid resource utilization has potential but given today’s technology levels, uncertain prospects for success.  Asteroids are hard to get to, have short visit times for round-trips, difficult work environments, and uncertain product yields.  Asteroids do have low gravity going for them.  In contrast, the Moon is close and has the materials we want in the form we need it.  The Moon is easily accessible at any time and is amenable to remote operations controlled from Earth in near-real time.  My perspective is that it makes the most sense to go to the Moon first and learn the techniques, difficulties and technology for planetary resource utilization by manufacturing propellant from lunar water.  Nearly every step of this activity – from prospecting, processing and harvesting – will teach us how to mine and process materials from future destinations, both minor and planetary sized-bodies.  Resource utilization has commonality of techniques and equipment, the requirement to move and work with particulate materials, and the ability to purify and store the products.  Learning how to access and process resources on the Moon is a general skill that transfers to any future space destination.

There was a reason that the Moon was made our first destination in the original Vision for Space Exploration.  It’s close, it’s interesting, and it’s useful.  Establishing a foothold on the Moon opens up cislunar space to routine access and development.  It will teach us the skills of a space faring people.  It makes sense to go there first and create a permanent space transportation system.  Once we have that, we get everything else.

Destination: Moon or Asteroid?

Part I:  Operational Considerations

Part II: Scientific Considerations

People at an asteroid: What will they do there?

Part II:  Scientific Considerations

In my last post, I examined some of the operational considerations associated with a human mission to a near Earth asteroid and how it contrasted with the simpler, easier operations of lunar return.  Here, I want to consider what we might do at this destination by focusing on the scientific activities and possible return we could expect from such a mission.  Some of the operational constraints mentioned in the previous post will impact the scientific return we expect from a human NEO mission.

Asteroids are the left over debris from the formation of the Solar System.  Solid pieces of refractory (high melting temperature) elements and minerals that make up the rocky planets have their precursors in the asteroids.  We actually have many pieces of these objects now – as meteorites.  The rocks that fall from the sky are overwhelmingly from the small asteroids that orbit the Sun (the exception is that in meteorite collections, some come from larger bodies, including the Moon and Mars).

Moreover, we have flown by almost a dozen small bodies, orbited two, impacted one and “landed” on two others.  Thousands of images and spectra have been obtained for these rocky objects.  The chemical composition of the asteroids Eros and Vesta have been obtained remotely.  We have catalogued the craters, cracks, scarps, grooves and pits that make up the surface features of these objects.  We have seen that some are highly fragmental aggregates of smaller rocks, while others seem to be more solid and denser.  In addition to these spacecraft data, thousands of asteroids have been catalogued, mapped and spectrally characterized from telescopes on the Earth.  We have recognized the compositional variety, the various shapes, spin rates and orbits of these small planetoids.  We now know for certain that the most common type of meteorite (chondrite) is derived from the most spectally common type of asteroid (S-type) as a result from the Hayabusa mission, the world’s first asteroid sample return.

In short, we know quite a bit about the asteroids.  What new knowledge would we gain from a human mission to one?

Although we have (literally) tons of meteorites, extraterrestrial samples without geological context have much less scientific value than those collected from planetary units with regional extent and clear origins.  Many different processes have affected the surfaces of the planets and understanding the precise location and geological setting of a rock is essential to reconstructing the history and processes responsible for its formation and by inference, the history and processes of its host planet.

Most asteroids are made up of primitive, undifferentiated planetary matter.  They have been destroyed and re-assembled by collision and impact over the last 4.5 billion years of Solar System history.  The surface has been ground-up and fragmented by the creation of regolith and some details of this process remain poorly understood.  But in general terms, we pretty much know what asteroids are made of, how they are put together, and what processes operate upon their surfaces.  True enough, the details are not fully understood, but there is no reason to suspect that we are missing a major piece of the asteroid story.  In contrast, planetary bodies such as the Moon have whole epochs and processes that we are just now uncovering – in the case of the Moon, water has been recently found to be present inside, outside and in significant quantity at the poles, relations that have enormous implications for lunar history and about which we were nearly totally ignorant only a couple of years ago.

Most NEOs will be simple ordinary chondrites – we know this because ordinary chondrites make up about 85% of all meteorite falls (an observed fall of a rock from the sky).  This class of meteorite is remarkable, not for its diversity but for its uniformity.  Chondrites are used as a chemical standard in the analysis of planetary rocks and soils to measure the amounts of differentiation or chemical change during geological processing.  In themselves, chondrites do not vary (much) except that they show different degrees of heating subsequent to their formation, but not enough heating to significantly change their chemical composition.

Some NEO asteroids are pieces of bigger objects that experienced chemical and mineral change or differentiation.  Vesta (not a NEO, but a main belt asteroid) has reflection spectra similar to known, evolved meteorites, the eucrite group.  These rocks suggest that some asteroids are small, differentiated planetoids, having volcanic activity that dates from the very beginning of Solar System history.  Moreover, since we have pieces of the Moon and Mars as meteorite fragments, some NEOs may consist of material blasted off these planets.  However, given that most NEOs are inaccessible to human missions, the likelihood that we could visit one of planetary derivation is small (curious that the most interesting of the NEOs appear to be those derived from some bigger (planet-sized) object.)  In broad terms of meteorite science, multiple small samples from a variety of asteroid types are preferable to many bigger samples of a single specimen, exactly the opposite of what a human mission will provide.

What specifically would a crew do during a NEO visit?  An astronaut on a planet typically would explore the surface, map geological relations where possible, collect representative samples of the units and rock types that can be discerned, and collect as much mapping and compositional data as possible to aid in the interpretation of the returned samples.  In the case of a NEO, many of these activities would not be particularly fruitful.  The asteroid is either a pile of rubble or a single huge boulder.  Chondritic meteorites are uniform in composition, so geological setting is not particularly instructive.  We do have questions about the processes of space weathering, the changes that occur in rocks as a result of their exposure to space for varying lengths of time.   Such questions could be addressed by a simple robotic sample collector, as the recently approved OSIRIS mission plans to do.

One question that could be addressed by human visitors to asteroids is their internal make-up and structure.  Some appear to be rubble piles while others are nearly solid – why such different fates in different asteroids?  By using active seismometry (acoustic sounding), a human crew could lay out instruments and sensors to decipher the density profile of an asteroid.  Understanding the internal structure of an asteroid is important for learning how strong such objects are; this could be an important factor in devising mitigation strategies in case we ever have to divert a NEO away from a collision trajectory with the Earth.  As mentioned in my preceding post, the crew had better work quickly – loiter times at the asteroid will probably be short, on the order of a few days at most.

Although we can explore asteroids with human missions, it seems likely that few significant insights into the origins and processes of the early Solar System will result from such exploration.  Such study is already a very active field, using the samples that nature has provided us – the meteorites.  Sample collection from an asteroid will yield more samples of meteorites, only without the melted fusion crusts that passage through the Earth’s atmosphere creates.  In other words, from this mission, scientific progress will be incremental, not revolutionary.

In contrast, because they yield information on geological histories and processes at planet-wide scales, sample collection and return from a large planetary body such as the Moon or Mars could revolutionize our knowledge of these objects in particular and the Solar System in general.  Many years prior to the Moon missions, we had meteorites that showed impact metamorphic effects but the idea of impact-caused mass extinctions of life on Earth only came after we had fully comprehended the impact process recorded in the Apollo samples from the Moon.  The significance of impact-related mineral and chemical features were not appreciated until we had collected samples with geological context to understand what the lunar samples were telling us.

Of course, science being unpredictable, some major surprise that could revolutionize our knowledge may await us on some distant asteroid.  But such surprises doubtless await us in many places throughout the Solar System and the best way to assure ourselves that we will eventually find them is to develop the capability to go anywhere in space at any time.  That means developing and using the resources of space to create new capabilities.  I will consider that in my next post.

Destination: Moon or Asteroid?

Part I:  Operational Considerations

Part III: Resource Utilization Considerations