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Statement by Wes Huntress Before the Subcommittee on Space and Aeronautics
Statement by Wes Huntress Before the Subcommittee on Space and Aeronautics
3 Apr 2001
(Source: American Astronomical Society)

Statement of
Dr. Wesley T. Huntress, Jr.
Geophysical Laboratory
Carnegie Institution of Washington

before the

Subcommittee on Space and Aeronautics
Committee on Science
U.S. House of Representatives

"Grand Challenges for America's Space Program"

America has the right stuff for an exciting space program.

Mr. Chairman and Members of the Subcommittee:

I am glad to be here today to discuss with you ideas on concepts for the future of this Nation's space program. I would like to outline for you a vision of how this country can establish a roadmap to the future for NASA based on its current capabilities-a roadmap for a systematic, logical, science-driven adventure in exploring our Solar System and unlocking the mysteries of the Universe.

America's space program has survived three decades of national depression, cynicism and cultural malaise after the Apollo 11 landing. The successes of the space program in the 1990's-Hubble's magnificent discoveries in the Universe, Mars Pathfinder's landing and rover on Mars, NEAR's asteroid reconnaissance and landing, Mars Global Surveyor's discoveries of water on Mars, Galileo's discovery of oceans below the surface of the Jovian moons, Lunar Prospector's tantalizing hint of water at the Lunar poles, the Shuttle flights and Space Station construction-all have provided a perfect opportunity to rekindle that intense feeling of pride, accomplishment and sense of national future when Armstrong stepped onto the Moon. We had a sense of national purpose in our space program back then. We lost it in 1972 and we need to recover that sense of purpose again at the beginning of this new 21st Century.

I believe that a well-thought-out, gradual program of exploration in which each step learns from the last, and in which infrastructure for conducting that exploration builds from the last, will be a far more effective, affordable and sustainable program for the American public. An immediate sprint mission to Mars with a large step in NASA funding, for example, is neither realistically affordable nor in the best long-term interest of space exploration. We have ample evidence for that in the Apollo legacy. Rather, let's define a long-term program that builds slowly, gradually and systematically, a program that will establish a permanent presence at each outpost along the way, so that we build the communications, transportation and other logistical infrastructure as we go.

Finally, it is not the particular vision that I present to you today that is particularly important. What is important is that it provokes thinking about the goals and strategy for space exploration in the next century.

The public wants an adventurous space program.

So does the American public want to explore space? And if so, then how do we give them a program that will generate exciting discoveries and build the adventure in a systematic and efficient manner?

First, it is demonstrably clear that the public want this country to explore space. The public response to the exciting events in its space program has been overwhelming. Ask any schoolchild in your District about Hubble. Their eyes will light up. The Mars Pathfinder landing and Sojourner rover brought a huge public following. The loss of the Mars missions in 1999 brought a large public groan of disappointment, but did not dampen their excitement for continuing Mars exploration.

Second, the public has a quite specific interest in space exploration that was brought to the surface by the 'Mars Rock', and by the discovery of both sources of water on Mars and a subsurface ocean on Europa, and by the discovery of extra-solar planets. Put simply, the public has an in-born interest in knowing if we are alone in the Universe and whether there is now or ever was life elsewhere beyond the Earth.

Talking to school children, people sitting next to me on the airplane, or where ever I go people light up at idea of space exploration and what we might find 'out there'. I am convinced that Americans want and need to have an exciting space exploration program. Exploration is an essentially American characteristic. How else did we open up the West, conquer the extremes of this planet, and finally establish the world's premier space exploration program? The time and opportunity is now to identify for our people quite specific goals for the space program, and most importantly goals that resonate with the American public's interests and not necessarily with those of the insiders in the space program.

The public wants answers:

The public now has a story of the history of the Universe that they can relate to their own lives. The Universe had a beginning; it was born in the Big Bang. It is aging and evolving. Stars are the individuals inhabiting the Universe. They live in families and have local neighborhoods. They live in massive city-states called galaxies. Stars are born, live, change and die. When stars die, they bequeath a new wealth of atomic matter to their progeny in the interstellar medium.

The Universe has become personalized in this way, and concepts such as 'origin', 'fate', 'death', 'other places' and 'life elsewhere' now have become more familiar when applied to the Universe. These concepts also evoke innate questions that crawl up from the depths of the human mind in moments of contemplation.

Questions like:

"Where did we come from?" This is a question that bears on the concept of 'origins'; the Big Bang, the origin of the Universe, and the origin of galaxies, stars, planets and life. How did life originate on the Earth and evolve to make the human species?

"What will happen to us?" What will happen to our own planet and to the Universe itself? This question goes to the concepts of fate and death in the Universe and brings to mind places in the Universe where bizarre and violent death occurs, such as exploding stars and Black Holes. The changing and violent nature of the Universe was demonstrated for the public right in our own cosmic back yard by the collision of comet Shoemaker-Levy with Jupiter.

"Is the Earth unique? Are there planetary systems around other stars and other planets like our own?

"Are we alone?" This is the most profound question of all. Does life exist beyond the Earth? Was there ever life on Mars or elsewhere in our Solar System? Do civilizations exist on planets around other stars?

These are questions that we now have to audacity to believe we can answer in the space program. And we believe it because the point has been reached in space technology development where we can actually design the instruments that will credibly allow us to get answers.

Mission From Planet Earth.

I believe that the basis for answering these questions, and for defining the future of the space program, already has its roots at the NASA. The Space Science Enterprise in NASA has based its approach to the next Millennium on these very same very public questions. It has a mission statement that directly addresses them. This mission statement is cast in the language of the public, was constructed with the help of representatives of the public, and is readily understandable. It consists of four simple phrases:

  1. Solve mysteries of the Universe,
  2. Explore the Solar System,
  3. Discover planets around other stars,
  4. Search for life beyond Earth.
Anyone can understand these goals, they are in plain English, and the public has demonstrated a resonance with these goals. The equivalent must also be established for human space flight. At the moment, Space Science is the only 'mission from planet Earth' program in NASA. It is traveling outward from Earth exploring other worlds and it is looking outward from Earth solving mysteries of the Universe.

On the other hand, the human space flight program is restricted to Earth orbit for the foreseeable future. It is not yet going anywhere, which is why it has not enjoyed the necessary level of public support. Until we know where human space flight is going, it will continue to struggle to find the support that it used to enjoy 30 years ago.

It is possible to put together a plan for human space exploration that will find resonance with the public, but it has a price; the fact must be accepted that the public and the Treasury are not yet ready for an all-out assault on Mars. We do not yet know the value of sending humans to Mars. We know too little about sending humans on a two-year journey to the surface of a far-flung planet. We have even forgotten how to go to the Moon-we've thrown away all the hardware that got us there last time. We need to learn to walk again before we run, and when we do run let's make sure that it is worth the effort.

So what should be the vision for human space flight, and where should it go? Space exploration is done by two complementary means-with robots and with humans. If it is true that goals should be defined independent of means, and that the method of implementation is a choice after having set the goals, then the goals of the human space flight program should be the same as those of the robotic space flight program. And both parts of the agency ought to work in partnership towards achieving them. There should be no trouble imagining a combined robotic and human space flight program addressing the same goals that Space Science has found to be resonant with the public. Human exploration has the potential to contribute to all of these goals. If properly woven together, robotic and human space flight could together provide for a very productive and cost beneficial 'mission from planet Earth.'

Grand Challenges.

I would like to suggest a set of Grand Challenges for the American space program at the outset of this new Millennium. They relate directly to the goals the Space Science Enterprise in NASA has already adopted. These are challenges that set long-term goals for the agency and provide a context for establishing a systematic approach to exploring the solar system with both robots and humans.

First, to read the history and the destiny of the Solar System. How did it come to be, what is its fate and what does its origin and evolution imply for other planetary systems.

Second, to look for evidence of life elsewhere in the Solar System. At Mars, at Europa, wherever in the history of the Solar System there has been liquid water or where it is discovered to exist now.

Third, to image and study planets around other stars. Ultimately, to find Earth-like planets in other planetary systems.

Fourth, to send a spacecraft to a nearby star. Something we don't know how to do today! But in 1900 we didn't how to fly either.

And Fifth, while addressing these challenges to conduct a progressive and systematic plan of human exploration beyond Earth orbit.

What can be expected to come from these challenges? To answer that, let's examine how each of these challenges might be addressed.

Grand Challenges #1 and #2. Read the History and Destiny of the Solar System, and Look for Evidence of Life Elsewhere in the Solar System.

The first two Grand Challenges, reading the history and destiny of the Solar System and looking for evidence of life elsewhere in the Solar System, are both about exploration of the Solar System. So let's examine them together, and take a look at the potential objects of exploration from the easiest to the hardest.

Near-Earth Objects.

Near-Earth objects (NEOs), such as asteroids and comets, are the easiest to get to in terms of the energy required. A fleet of micro-spacecraft can be sent to explore a large number of these small objects to survey their bulk properties and to understand their diversity. This will help understand how to mitigate against them should any one of them present a danger to Earth in the future. Other products from this survey include an understanding of the origin of asteroids, their role in the formation of planets, their potential for supplying resources either for future space exploration or for export to Earth, and any potential need for human missions to these objects.

The Moon.

Next in order of ascending difficulty to explore after NEOs is the Moon. Additional energy is required in this case to drop safely into the Moon's gravitational well and back again. There are many reasons to go back to the Moon, both for science of the Moon as well as science on the Moon.

Among the most important science to be done at the Moon is related to reading the history of the Earth/Moon system.

Age dating of lunar stratigraphy with analysis of the implanted solar wind in these layers can be used to determine the past history of the Sun and it's future evolution.

The frequency and size distribution of asteroid impacts on the Earth can be determined by exploring the cratering record on the Moon. The impact flux is the same on the Earth and Moon, but the Moon preserves its impact record in small craters while dynamic surface processes rapidly erase Earth's impact record. By identifying the craters formed over the last 100 million years or so on the Moon, the fine structure in the impact record can be examined for periodicity and size vs. flux in the lunar impactors.

While much of the preliminary work can be conducted with robotic missions under direct control from Earth, identification of the appropriate local sites, craters and selection of samples for analysis will most likely require human fieldwork on the Moon. We have had only a few such field investigations during the Apollo program, and many more are needed in order to elucidate further the history of the Earth-Moon system.


More difficult still than lunar exploration is exploration of Mars. There are three main reasons for the scientific exploration of Mars. First and most significant is to search for evidence of past or present life. It may even be necessary to extend the search below the surface from orbit with radar to look for subsurface ice and water environments, and from the surface with drills or other means to explore ice and water subsurface environments if they are found. Should any evidence be discovered by robotic missions for early or extant life, whether surface or subsurface, there is no doubt that human fieldwork on Mars will be required.

Other reasons to explore Mars are to understand Mars as a planet, how it has evolved, any potential resources that might be useful for future exploration, and to understand Mar's weather and climate history. All of these objectives, including the search for life, share a common thread-water. When in the planet's history was there liquid water, where was it, in what form was it (rain, rivers, lakes, and oceans) and how much was there?

The Outer Solar System.

The hardest to explore is the Outer Solar System, which almost certainly will be the exclusive realm of robotic exploration for the foreseeable future. This is the realm not just of the giant planets themselves, but of a large number of diverse satellites and free small bodies. Among the most interesting are Europa, with its potential for a subsurface ocean, Titan, which may have hydrocarbon fluids and organic snows on its surface, and cometary objects, which may contain the most primitive of Solar System material including pre-biotic organic compounds.

NASA is already on a path to determine if there is an ocean below the ice on Europa, including measurement of the distribution of subsurface water and where the ice above it is thinnest. If the existence of an ocean were confirmed, it would be imperative to go back again, this time to Europa's surface. The lander would melt through the ice and deploy a robotic submarine, an 'aquabot', in the subsurface ocean to search for signs of life. If the Cassini/Huygens mission to Saturn and Titan discovers lakes or oceans on Titan, then a follow-up mission should be sent to deploy global balloon explorers in the atmosphere. These 'aerobots' would carry drop probes to explore interesting parts of the surface, perhaps including 'aquarovers', robotic boats for exploration of any large bodies of liquid.

Robotic Outposts

To carry out such advanced exploration in our Solar System, I suggest considering the concept of a robotic outpost. A robotic outpost is a remote scientific research station similar to a human outpost, but operating autonomously using only robots. The lowest level of autonomy for a robotic outpost would be remote human operation where real-time interaction is possible, such as on the Moon. The highest level would be nearly complete autonomy where the robots would be given only the top-level goals, and they would determine their own immediate objectives in pursuit of those goals using only occasional consultation with remote human directors.

Robotic outposts would be a means to extend the human senses into the Solar System prior to human presence. They would be permanent and self-sustaining with occasional re-supply. They could be deployed as expandable intelligent stations in space or on the Moon, asteroids, Mars or elsewhere. They could conduct planetary in-situ studies or remote astrophysical observations, and they could set the stage for later human participation if and when it was decided to send humans.

Grand Challenge #3. Image and Study Planets around Other Stars.

There will come a time in the first half of the next century when humankind will be treated to the first image of an Earth-like planet around another star. That image will have an even larger effect on the human consciousness than did the first global image of Earth taken from space by Apollo 8 in 1968. We know now what technology will be used to obtain that image--space interferometry--but we have difficulty imagining the scope of its application to achieve the goal. It is the same as looking into the future at the beginning of this century believing that the airplane will be used some day to carry human passengers across the country, but with no idea how to imagine a Boeing 747.

The new generation space telescope, NGST, is being designed now as a lightweight deployable 6-8 meter optical system. It is possible to imagine even larger aperture space telescopes in the future as the technology matures, growing from to 20-m and to even larger 100-m sizes for thin-film apertures. Several of these large space telescopes, optically coupled as an interferometer over a baseline of 10,000 km, could accomplish extrasolar planet imaging.

The next generation of space telescopes must overcome the thermal environment and orbital viewing constraints suffered by Hubble in low Earth orbit. A good place to put the following generation would be in stable orbit at the Sun-Earth Lagrangian point L2. For interferometry, several telescopes in orbits about L2 achieve the proper baseline and more complete coverage for better images. The L2 stationary observation point is close enough to Earth for communication purposes, but far enough away to avoid Earth-related duty cycle and thermal problems. At these short distances, about 1.5 million km from Earth, human servicing of a complex of co-orbiting instruments is a feasible concept.

Grand Challenge #4. Send a spacecraft to a nearby star.

Once an earth-like planet is found orbiting another star, the need to develop the ability to send spacecraft to nearby stars will become acute. This challenge is even more daunting than producing an image of an extrasolar planet. We can identify the technology required for the latter, but we cannot yet identify the propulsion technology necessary to send even a micro-spacecraft to a nearby star, especially if it is to slow down and explore any local planetary system. The travel time must also be reasonable in human terms, on the order of a decade or so for travel to the nearest stars and no more than a century for the farthest target stars.

The amount of energy required to send even the smallest spacecraft to the nearest star is 3-4 orders of magnitude larger than any rocket we know how to build. Antimatter propulsion, fusion rockets and beamed energy are the only sources we can think of today, and the amount of propulsive energy required per year of flight is on the order of all the energy produced on Earth in one year.

Besides propulsion, there are many other breakthrough technologies required to meet this challenge including on-board intelligence, robotics, control, repair, navigation and communication. But even if the first technological steps we taken towards this goal, a great deal would be learned through each intermediate stage, and excellent space science would be accomplished along the way. Early flights could be done in the Solar System to test the propulsion system. Development of a propulsion system capable of only 1% of the required velocity for stellar flight, solar sails for example, would enable vastly shorter trip times and new navigational capability through the Solar System. Each successive stage in technology development could take us farther into the interstellar medium, first exploring the heliosphere and the Kuiper Belt, then the Oort Cloud, the interstellar medium, finally culminating with a flyby of Alpha Centauri.

Grand Challenge #5. Conduct a progressive, systematic plan for human exploration beyond Earth orbit.

This challenge is of a different character than the other four. The first four are challenges in science and discovery. This fifth is a challenge in implementation. While it is not yet conceivable how to send humans to the nearest star, there is a potential role for human exploration in three of these challenges. This makes it possible to construct a systematic plan for human exploration that progresses readily from the easiest of missions to the hardest. At each stage of this progressive plan, human explorers perform enabling functions.

The ultimate destination in the plan remains human exploration on the surface of Mars, but the capability to accomplish that mission is developed and tested over time in less risky missions along a natural evolutionary technological pathway. It is not a Mars-or-Bust program. It is a steady, progressive, strategic approach to human exploration that encompasses a lot more than just Mars exploration and which gets us to Mars with a robust capability and with much less risk than an all out assault on Mars.

The plan assumes that the Space Station exists. This assumption seems to be a good one at the moment, and if the Space Station exists then it should be used to best cost-effective advantage. The Station becomes the key space-borne logistical element at Earth. To illustrate the plan, let's start again with the easiest and earliest missions and then roll the program forward in time.

Construct and service a Mega Space Telescope Facility at L1 or L2.

If cost tradeoff studies for both large space telescopes and interferometers shows that construction, servicing and evolutionary development of these instruments in space is better accomplished by human missions than by robotic means, then an appropriate initial step for human exploration beyond Earth orbit would be to build a Deep Space Shuttle capable of ferrying humans and material from the Space Station in Earth orbit out to L2.

A Deep Space Shuttle would be needed which was capable of Earth escape from Station orbit, travel 1.5 million km to L2 and back, and support humans and construction-service requirements for a stay-time on the order of days to months. The energy requirement is minimal and less than for Apollo. The first Deep Space Shuttle would be a step in the evolutionary development of a vehicle that would eventually shuttle back and forth from Earth orbit to Mars orbit. Also, missions to the Lagrangian points remain close to Earth, within about a week's return flight time, and would give the astronauts experience with deep space travel and with operations in space on unanchored equipment-the next step beyond Hubble servicing.

Lunar surface exploration.

The next step in energy and hardware requirements relative to Lagrangian point missions would be to add the capability to drop into the lunar gravity well and climb back out. The Deep Space Shuttle would now be required to shuttle from the Station in Earth orbit to lunar orbit and carry a heavier payload. Two new pieces of hardware are also required; a Lunar Shuttle to ferry equipment and humans between the Deep Space Shuttle in lunar orbit and the lunar surface, and a Lunar Habitat to support human expeditions on the surface of the Moon.

The trip times to the lunar surface would be shorter than for Lagrangian point missions but stay time at the destination would be considerably longer. The Lunar Habitat would be emplaced initially by an unpiloted Lunar Shuttle trip. The first Lunar Habitat might be human tended, and used episodically to construct and develop a robotic outpost on the surface. This robotic outpost would be the first step in developing a combined robotic/human science outpost on the Moon in which the Habitat is enlarged and becomes fully operational.

Asteroid exploration.

Near-Earth asteroids are another potential target for human exploration. The energy requirements are less than for lunar surface exploration missions, but the distances are larger and trip times longer. It is not immediately obvious whether asteroid missions would be easier or more difficult than lunar surface missions. Trade-off studies might show that asteroid exploration should precede lunar surface exploration in a progressive, evolutionary human space flight program.

The Deep Space Shuttle would need new capabilities to support longer trip times, to maneuver and rendezvous with the asteroid and for station keeping during surface exploration. This latter function is made more difficult than for Lagrangian point missions because of the rotation of the asteroid. The Deep Space Shuttle must also support an asteroid surface explorer, a derivative or precursor to the Lunar Habitat, to ferry astronauts between the Deep Space Shuttle and the surface of the asteroid, and to support their exploration goals while there.

Phobos (or Deimos) Observatory.

After experience with progressively longer deep space flight from Lagrangian points to near-Earth asteroids, and with experience in exploration logistics at the Lagrangian points, asteroids and the Moon, and with surface habitat experience on asteroids and the Moon, the next target is Mars. By this time robotic missions to Mars will have shown Mars to be well worth this ambitious undertaking. When the decision is finally taken to go to Mars, the goal should be no less than to set up a long-term program of human exploration and eventual colonization. In this case the first step ought to be to set up a logistics base for space operations at Mars just as we have done at Earth--a Space Station in Mars orbit to support operations to and from the surface. Fortunately, there are two station platforms already provided in close orbit of Mars-Phobos and Deimos-ready to accept habitats for human beings.

A station on Phobos or Deimos would be human-tended initially and evolve into a permanent, rotated-crew facility. It would be set up on the Mars-facing side of the tiny moon and used for remote observations and study of Mars. The observatory would track surface changes, monitor Martian weather, and operate surface stations. Robotic surface probes would be launched from the station for scientific purposes and to emplace supplies.

The Phobos Station would be supported by the final generation of the Deep Space Shuttle, now capable of Earth orbit to Mars orbit operation. The Deep Space Shuttle would carry the station to Phobos and it would be set up and supplied from Earth using the Deep Space Shuttle. Initially a scientific observatory, in its ultimate configuration the station would be used also as the logistics base for ferrying humans and their equipment to the surface of Mars and back.

Mars surface exploration.

All of the necessary systems and support are now in place to set up a human outpost on the surface of Mars. The Deep Space Shuttle brings two new vehicles to the Phobos Station, a Mars -Orbit-to-Surface-Shuttle (MOSS) and a Mars Habitat. The first missions for the MOSS are robotic; to emplace the Mars Habitat and any necessary supporting hardware and supplies on the surface to supplement production by the long-operating robotic Mars Outpost. Having fulfilled this function, it is next piloted from Phobos to the surface by the first human surface explorers and stands ready to take them back for rotation with the next crew.

Beyond Mars.

Mars is as far as this vision of human exploration goes. But there are destinations beyond Mars that may beckon as we explore space in the next century. If our robotic missions find an ocean below the ice on Europa, and if our aquabots find things swimming in the European ocean, then the temptation to send humans will be unbearable. Right now we know of no way to shield humans from a swift death in the radiation environment of Europa, even inside a spacecraft, but perhaps they can be enclosed in a magnetically shielded cocoon of some kind until they are well underneath the natural ice shield of Europa's surface.

Who can predict what we will find as we proceed over the next years to investigate our Solar System and the stars beyond? Who could have predicted in 1990 all that we have learned since then about water on Mars, potential early life on Mars, oceans beneath the ice of Europa, planets around other stars, and the robustness and early origin of life on Earth?

What are the barriers, what needs to happen?

Nothing more than National will, which I believe is already there in the people of the United States. It is a matter for the Government of the United States to recognize it, to avert its gaze on quarterly reports for just a few moments to peer into the more distant future of the country. It is a matter for leadership by the Administration, and for support from Congress.

That national will of course must translate into funding. But the vision I have just outlined does not require an immediate large increase in the NASA budget. It does require commitment to a manifest destiny for America in space. It does require a commitment to the resources required to realize that policy as the space program gradually and systematically increases in scale and scope, but not so much in any one year as would be required for an immediate program to send humans to Mars now. I believe much of what I have put before you can happen with such a committment.

It should not take a crisis to make it happen. We will wait a long time before anything from space will ever threaten us; perhaps an asteroid, but even that possibility is statistically remote. It should be instead a matter of the will of a great nation and people, and a matter of national curiosity, of the human need to know, of the adventure of exploration.

And if there is the slightest chance that life may be out there, then we have to go.

This testimony is adapted from the Second Annual Carl Sagan Memorial Lecture delivered by the author at the American Astronautical Society Annual Meeting in Houston, TX, November 17, 1998.

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Last Updated: 5 Jun 2001