These remarks were given by John Marburger on March 15, 2006 during the Keynote Address of the 44th Robert H. Goddard Memorial Symposium in Greenbelt, Maryland.

The topic of this year's symposium, "Engineers, Scientists and the Vision," reflects the combination of mental attitudes needed to accomplish great things in space, and I am pleased to add a few thoughts of my own this morning on these topics.

I am always puzzled by debates over the Vision for Space Exploration because the choices are so constrained by physical reality. We humans dwell in a vast universe whose chief features only became apparent during the 20th century. We have known for a long time that a huge gap separates the objects trapped by the gravity of our star, the Sun, and everything else. Information about phenomena beyond that gap can come to us only through the rain of photons and other elementary particles spewed out by the awesome processes of the cosmos. Our observations of that part of space began in prehistoric times and they continue to sustain the growth of science in our era. Phenomena on our side of the interstellar gap, in what we call the solar system, are potentially amenable to direct investigation and manipulation through physical contact, and can reasonably be described as falling within humanity's economic sphere of influence.

As I see it, questions about the vision boil down to whether we want to incorporate the solar system in our economic sphere, or not. Our national policy, declared by President [George W.] Bush and endorsed by Congress last December in the NASA authorization act, affirms that, "The fundamental goal of this vision is to advance U.S. scientific, security, and economic interests through a robust space exploration program." So at least for now the question has been decided in the affirmative.

The wording of this policy phrase is significant. It subordinates space exploration to the primary goals of scientific, security and economic interests. Stated this way, the "fundamental goal" identifies the benefits against which the costs of exploration can be weighed. This is extremely important for policy-making because science, security and economic dimensions are shared by other federally funded activities. By linking costs to these common benefits it becomes possible, at least in principle, to weigh investments in space exploration against competing opportunities to achieve benefits of the same type.

I want to stress how very different this kind of thinking is from the arguments that motivated America's first great space vision, the Apollo program. President [John F.] Kennedy launched the Apollo program during an intense period in the Cold War, four years after the Soviets launched the first Sputnik satellite. In his 1961 message to Congress, Kennedy said of sending a man to the Moon and returning him safely that, "No single space project in this period will be more impressive to mankind, or more important in the long-range exploration of space; and none will be so difficult or expensive to accomplish. ..."

The tone of this message clearly conveys the intention to send a signal to the world that America will lead the way into space, and this spirit remains a vital factor in our ability to accomplish great feats of engineering to get us there. The Apollo program was what mathematicians call an "existence proof" -- a demonstration that a problem does have a solution and that efforts to discover its details will not be in vain. Like all firsts, it was unique. No subsequent space endeavor can be quite like it.

President Bush's vision also declares the will to lead in space, but it renders the ultimate goal more explicit. And that goal is even grander. The ultimate goal is not to impress others, or merely to explore our planetary system, but to use accessible space for the benefit of humankind. It is a goal that is not confined to a decade or a century. Nor is it confined to a single nearby destination, or to a fleeting dash to plant a flag. The idea is to begin preparing now for a future in which the material trapped in the Sun's vicinity is available for incorporation into our way of life.

Given the expense of climbing out of Earth's gravity well, the natural course of space development begins with objects trapped in Earth orbit, including the Moon, followed by objects trapped in solar orbits near the Earth's, and then extending opportunistically to other destinations.

The first stage of exploiting cislunar space is already well advanced, partly because applications have been found that can be achieved with small payloads and yet whose value to society exceeds the cost of launch. It is likely that these near-Earth applications will always dominate the use of space because Earth is where the people are, as well as the environment that sustains them. We must never forget that within our solar system the object most important for humankind is Earth, and Earth-oriented space applications merit priority in a balanced portfolio of public investment.

The Moon has unique significance for all space applications for a reason that to my amazement is hardly ever discussed in popular accounts of space policy. The Moon is the closest source of material that lies far up Earth's gravity well. Anything that can be made from lunar material at costs comparable to Earth manufacture has an enormous overall cost advantage compared with objects lifted from Earth's surface. The greatest value of the Moon lies neither in science nor in exploration, but in its material. And I am not talking about mining helium-3 as fusion reactor fuel. I doubt that will ever be economically feasible. I am talking about the possibility of extracting elements and minerals that can be processed into fuel or massive components of space apparatus. The production of oxygen in particular, the major component (by mass) of chemical rocket fuel, is potentially an important lunar industry.

What are the preconditions for such an industry? That, it seems to me, must be a primary consideration of the long-range planning for the lunar agenda. Science studies provide the foundation for a materials-production roadmap. Clever ideas have been advanced for the phased construction of electrical power sources -- perhaps using solar cells manufactured in situ from lunar soil. A not-unreasonable scenario is a phase of highly subsidized capital construction followed by market-driven industrial activity to provide lunar products such as oxygen-refueling services for commercially valuable Earth-orbiting apparatus. This is consistent with the space policy statement that the U.S. will "Develop the innovative technologies, knowledge and infrastructures both to explore and to support decisions about the destinations for human exploration."

I watched the live video coverage of Neil Armstrong taking the first footsteps on the Moon, and I was tremendously excited by it. To actually do something productive on the Moon would validate and justify the risk and expense of those early ventures and create an entirely new level of excitement. The operations I have described are intricate but many could be accomplished robotically. It is difficult for me to imagine, however, that such a complex activity could be sustained without human supervision and maintenance. This, in my view, is the primary reason for developing the capacity for human spaceflight to the Moon. It is a pragmatic reason and more likely to be sustainable over the decades necessary for success than curiosity or even national prestige.

Where does Mars fit into this picture? At the present time, much commentary to the contrary, we do not know how to send humans to Mars and return them safely within a reasonable cost envelope. The whole point of the vision, however, is to make the solar system accessible, and Mars and the asteroids whose orbits penetrate Mars orbit are the nearest objects suitable for development beyond the Moon (I am excepting Venus for its high-surface temperature). The current vision policy document says the U.S. will "[e]xtend human presence across the solar system, starting with a human return to the Moon by the year 2020, in preparation for human exploration of Mars and other destinations." It does not propose a date for a human Mars mission. The cost and safety of a human Mars mission are very scenario-dependent, and I hesitate to say anything more about it.

There is no question, however, that the expense of such a mission would be vastly reduced if the bulk of its fuel and massive components could be obtained from materials, and manufactured, outside Earth orbit. The Moon is a logical place to do this. As to the motivation for a human expedition to Mars, there is an obvious prestige value for a nation that leads the first human-to-Mars mission. A more pragmatic objective is to establish on Mars the same kind of industrial infrastructure that I described for the Moon. What makes the Moon operation economically viable are the Earth-oriented markets. That is not likely to be the case for a similar operation on Mars unless economically attractive materials are found on Mars itself, or among the asteroids. Consequently, a Mars operation complex enough to warrant human oversight will have to be fully subsidized by governments during a long period of robotic exploration beyond Mars orbit.

It should be obvious from these remarks that I believe the vision President Bush set forth on January 14, 2004, is not one for a few decades, but for a much longer period of space development. That is why the vision emphasizes the need to "[i]mplement a sustained and affordable human and robotic program to explore the solar system and beyond."

To be sustainable, the space exploration budget must grow at the same rate as the domestic discretionary budget. To be affordable, its fraction of that budget must be small enough to be stable against competition from other parts of the budget, and in particular those that are perceived to serve a wider variety of societal needs. And yet it must be large enough to carry the project forward and sustain the necessary community of technical people. I know there are concerns that space science may suffer by competition with the perpetually expanding space exploration theme. But science is one of those primary objectives that space exploration is supposed to accomplish and it has much popular support. I believe that in the long run space-science funding will remain at levels strong enough to support a healthy program.

John Marburger is director of the Office of Science and Technology Policy, Executive Office of the President.

NOTE: The views of this article are the author's and do not reflect the policies of the National Space Society.

Visit SPACE.com/Ad Astra Online for more news, views and scientific inquiry from the National Space Society.