Colonizing Space With Fusion Propulsion

August 8, 2009 (LPAC)-- The following article from our archives, was written by Friedwardt Winterberg for the April 1981 edition of Fusion Magazine. Friedwardt is a former member of Lyndon LaRouche's Fusion Energy Foundation, a science foundation which enjoyed a subscribing base of over fourteen-thousand members, and was the nation's largest scientific membership organization before it was shut down in the 1987 government attacks on LaRouche and his organization.

Colonizing Space With Fusion Propulsion

by Dr. Friedwardt Winterberg

Chemical rockets can take man to the Moon but not beyond. But with fusion-propulsion rockets; man will be able to colonize distant planets and, one day, the entire galaxy.

The four great technological breakthroughs of the 20th century are manned flight, the discovery and harnessing of nuclear fission, the development of the space rocket, which led to the 1969 Apollo Project Moon landing, and controlled thermonuclear fusion. The first three breakthroughs have already been accomplished; the harnessing of fusion power will be accomplished during the remainder of the century, probably not later than 1985.

I do not consider myself a practitioner of the pseudoscience of futurology, which attempts to predict the future by making extrapolations from present trends. Such an endeavor is difficult, to say the least, because the future is determined largely by inventions and discoveries that have not yet been made. But as relativity theory tells us, the past, present, and future are closely connected to each other. And if we know something about the present, we should be able to know something about the future.

Our present state of scientific knowledge and technological advancement tells us something about the discoveries
and revolutionary technological advances man can expect to achieve during the rest of this century and beyond it.
The importance of achieving controlled thermonuclear fusion ranks with the invention of fire. But fusion is a new kind of fire; it is the ignition of a small star on Earth. In contrast to ordinary chemical fire, fusion requires temperatures of
100 million degrees, like those that exist in the center of stars, like our Sun.

The Discovery of Thermonuclear Energy

One of the great problems that engaged scientists dur­ing the last century was to explain how the Sun could have shined the billions of years necessary to have made evolution possible. At the turn of the century, Lord Ray-leigh told Darwin, I have given you only a few million years for your evolution to take place, because that is as long as the Sun could have given off heat by slowly shrinking in size. No other process to do that was known at the time. But Darwin knew that he would need billions of years to explain evolution. There was a great deal of anxiety in scientific circles about the problem, and when radium was discovered, giving the first clue about nuclear energy, some scientists speculated that the Sun might be made out of radium. But, of course, it is not.

Then, when the Special Theory of Relativity was discovered by Einstein and Poincare, in which ? = mc2, and we learned that there was an enormous amount of energy in matter, the question then became, how is it released? That problem was subsequently resolved in 1928, when it was shown that at extremely high temperatures, certain light nuclei reacting through thermonuclear reactions would produce large amounts of energy. Even so, two years later at a famous conference of physicists, England's Lord Rutherford maintained that the idea of releasing thermonuclear energy on Earth was totally in the realm of fantasy and would never be realized. A few years later, thermonuclear fission was discovered.

One can see from this account how fast knowledge progresses. Futurologists should be careful in making their predictions.

The discovery of fission provided man with two great benefits: an unexpected source of energy and a "match" big enough to light a much larger thermonuclear reaction—fusion. A great deal has been said about the use of fusion energy for the generation of electrical power. Power generation, however, is only one application of fusion; another major application is its unique significance for spaceflight.

Rocket Propulsion

The great challenge that future spaceflight poses is the development of rocket-propulsion systems that can carry large payloads at extremely high speeds, thereby making possible manned spaceflight to distant planets. The Apollo program demonstrated that we are able to land man on another planet in the solar system, but not with a very large payload. The Moon is relatively near to the Earth. If we were to attempt to go to Mars with chemical propulsion, it would take years, and the astronauts would have to travel in a spacecraft not much bigger than the interior of a bus. Making sure that nothing would go wrong in such a small vehicle traveling for years would be very difficult. Such an environment is clearly not practical for long-term space travel.

Artist's depiction of activity at a modularized space station in Earth orbit. The components of the station would be transported to Earth orbit by the space shuttle. Artist's rendition of the Orbiter space shuttle leaving Earth's atmosphere for orbital flight.

Chemical propulsion is adequate only for unmanned space probes. However, unmanned probes for scientific reasons alone are neither desirable, nor can they lead to the goals that we must accomplish. What will we find on Mars or elsewhere in the solar system? Only man, with his versatility of mind, is able to respond to totally unexpected experiences. Pre-programmed robots cannot do that.

It is only with fusion propulsion— fission is also inadequate—that manned spaceflight to distant planets will become practical. And man not only will be able to explore the solar system; he will be able to colonize and industrialize it. This is one reason why everyone working with fusion is so excited.

The crucial problem in rocket propulsion is to achieve a very large exhaust velocity. The key performance parameter is specific impulse or the impulse per unit weight of the rocket propellant, measured in seconds:
ma(At/mg) = ??/g.

The hotter the gas, the greater the motion of the gas molecules and hence the exhaust velocity of the gas. Therefore, the extremely high-temperature and high-velocity products of a fusion reaction—106 meters per second—give fusion propulsion systems a very large potential specific impulse of 100,000 seconds. Chemical rockets have maximum specific impulses of less than 450 seconds, and fission systems less than 1,000 seconds.

When a chemical fuel is burned, the gas molecules and hence the exhaust reach a velocity on the order of a few kilometers per second, at best 3 kilometers or about 2 miles per second. Such a fuel, composed of hydrogen mixed with oxygen, is the most powerful rocket fuel we know and was used in the upper stage of the Saturn rocket.

As we know from rocket theory, rocket velocity can be increased to as much as three times more than exhaust velocity using a three-stage rocket system. In fact, to escape the Earth's gravitational pull, it is necessary to attain a rocket velocity of about 12 kilometers per second, which can be accomplished only with a multistage rocket. Each stage can attain a velocity of about 3 kilometers per second; and when three stages are put on top of each other, the spaceship can escape the Earth's gravitational field and head for the Moon. However, the maximum velocity that can be attained with chemical propulsion is 10 to 20 kilometers per second.

Chemical propulsion, adequate for escaping the Earth's gravity, thus does not permit us to travel to Mars in a time less than years. The trick of getting to Mars in a short time, possibly only weeks, is to use a higher exhaust velocity. This requires a propulsion fuel that has a much larger energy density and thus higher combustion temperature.

The answer is thermonuclear propulsion. In a thermonuclear reaction, the temperatures are not a few thousand degrees, as in chemical combustion; they are typically a hundred million degrees. Using fusion propulsion, we can get an exhaust velocity on the order of not just a few kilometers per second, but a few thousand kilometers per second.

The idea is to launch a fusion space rocket that would be assembled in orbit, where there is no gravity and it is therefore possible to build much larger structures. All of the different parts and materials for the space rocket would be carried up into orbit by chemically propelled space shuttles (to go from a planetary surface to an orbit, chemical propulsion is always the most convenient means). The rocket constructed in this fashion could carry a payload of thousands or even millions of tons, which it would take from an Earth orbit into an orbit around Mars. Then man would descend onto the surface of Mars, using chemical rockets.

Thermonuclear Microexplosions

The kind of fusion reaction that would propel this rocket would consist of many microexplosions, small releases of nuclear energy many orders of magnitude smaller

than from a hydrogen bomb. This is the fusion process known as inertial confinement. Magnetic fusion, for reasons I will not go into here, is not very suitable for rocket propulsion; but inertial-confinement fusion, fortunately, is ideally suited for it. In inertial-confinement fusion, lasers or other types of beams ignite thermonuclear explosions that are small enough to be confined in a container for power production or to be used for rocket propulsion.

Rocket engineers have always dreamed of a rocket propulsion system that had both a very high specific impulse—a very high exhaust velocity—and a very high thrust. For example, in a chemical propulsion system like the Saturn rocket you have a very high thrust, several thousand tons, but the exhaust velocity is only 1 or 2 kilometers per second.
Another system that has been under investigation is ion propulsion, in which the spacecraft is propelled by a beam of accelerated ions. Such a system would have a high specific impulse, but its thrust would be very small. Thus, using ion propulsion would again take years to travel to Mars, because it would take such a long time to accelerate the spacecraft to a large velocity.

The specific impulse, measured in seconds, is the impulse per unit weight—the higher the specific impulse, the more efficient is the power source. The thrust is the force produced by the exhaust. Only with a microexplosion fusion propulsion system do you have both high specific impulse and very high thrust. In its capabilities relative to ordinary chemical propulsion, fusion propulsion is like going from a rowboat to a steamboat.

In a fusion-propulsion system, the beams of photons or particles would ignite fuel pellets, each the size of an aspirin tablet, which on explosion would typically produce the energy equivalent of 10 tons of TNT. The microexplosions would take place in the focus of a concave magnetic mirror, whose magnetic field would be generated by superconducting magnetic field coils. As the sequence of microexplosions takes place, perhaps one per second, the fireball of each microexplosion would be reflected by the magnetic mirror, resulting in the thrust that would propel the spacecraft. (See Figures 1 and 2.)

We see that the development of fusion rocket systems requires the combination of two technologies: fusion, which takes place at extremely high temperatures; and superconductivity, an extremely low-temperature technology. The fireballs of the microexplosions are so hot that they cannot be allowed to come in contact with the spacecraft. This problem is solved very elegantly by shield­ing the spacecraft with a magnetic field generated by superconducting magnets, which are cooled using liquid helium. It should be added that in the case of travel within our solar system, the exhaust velocity of a fusion rocket may get too high, and we may want to reduce it by adding propellant hydrogen to the exhaust.

The idea of propelling a rocket by a sequence of explosions is a very old one. The idea was proposed by an engineer by the name of Ganswindt around the turn of the century in Berlin. However, he was not a physicist and could not correctly analyze his conception. Around the same time, an Austrian physicist working at the University of Lemberg in Czechoslovakia (now in the Soviet Union) analyzed the concept and showed that the chemical explosives known at the time would not be strong enough to propel a space rocket. However, Ganswindt prophetically predicted that one day man would find a propulsion explosive that would be large enough. In fact, less than 40 years later, such a powerful explosive was discovered by Hahn and Strassmann, in the form of nuclear fission.

After fission was discovered, scientists at Los Alamos National Scientific Laboratory pointed out that one could propel a rocket by a sequence of exploding atomic bombs. This approach to rocket propulsion was extensively studied in Project Orion, but it was eventually abandoned because it was considered very adventurous to use a sequence of atomic bomb explosions to propel a spacecraft. Looking back, the project does not seem overly adventurous, and many people think it was a mistake to abandon it.

Nevertheless, for the last 15 years, there has been a much more exciting possibility—that of reviving the project using inertial-confinement fusion—mini H-bombs— which is a much more effective method.
Recall that the hydrogen or fusion bomb is always ignited using an atomic or fission bomb as a trigger, which then sets off the much larger thermonuclear explosion. Earth orbit, carrying the materials needed to construct a Until the mid-1960s, this was the only known method of fusion-propelled superrocket. Such a spaceship will be able to carry a large crew as well as heavy equipment such as earth-moving machines. This spaceship could travel to Mars. It could also be used as a tugboat to travel to and colonize the Moon. To date, we have only landed on the Moon and inspected a few acres. But with our fusion-propelled superrocket, we would be able to go into lunar orbit, descend to the surface of the Moon with chemical rockets, unload necessary materials, and build a lunar colony. (See Figure 3.)

Figure 3 WINTERBERG'S PROPOSAL FOR MOON MINING: Winterberg suggests that a series of nuclear explosions could be used to
tunnel to the center of the Moon and extract its valuable metals. In the background is a lunar landscape taken on the last lunar manned flight, Apollo 17 in 1972.

What would be the point of establishing a lunar colony? Although the Moon has no water, it has a core where very valuable metals are concentrated, metals that may eventually run out on Earth. Retrieving these metals is essential fusion research, believes that this application of fusion for the future of civilization.

Dr. Edward Teller, one of the pioneers in the field of fusion research, believes that this application of fusion will precede the use of fusion in commercial power plants. To build and expand a technological civilization, there I am not sure I agree with this prediction. Nevertheless, Teller's viewpoint underlines the nearness of rocket propulsion using thermonuclear microexplosions.

Where do we stand experimentally? The highly publicized laser beams are only one method of igniting thermonuclear microexplosions. An even more promising method uses beams of particles. Particle beam weapons are now under development in the United States and in the Soviet Union. Clearly, if we can produce a particle beam that can be used as a weapon, we can produce a particle beam that will set off a miniature hydrogen explosion. In fact, inertial-confinement fusion must be achieved before the weapons project can even be considered, because the latter requires much more powerful beams. With the beams under development at the San-dia National Laboratory in the United States and at the Angara facility in the Soviet Union, inertial-confinement fusion will soon become a reality.

These facilities will produce high-energy beams of ions or electrons. If these particle beams are shot at a thermonuclear pellet from many sides at once, the pellet will explode. Although this has not yet been accomplished, it should occur in the near future—unless our physics calculations are greatly in error. As soon as we succeed in producing this miniature explosion, a fusion rocket propulsion system will quickly follow.

Mining on Other Planets

Once we have developed fusion-propulsion systems, we will be ready (FIGURE 3) are basically two things required: metals such as steel and the minerals that go into making them, and other raw materials that can serve as energy sources. The minerals that are available to us on Earth are the small proportion that are in the Earth's crust. But the heavy metals we need have been pulled down to the center of the planet by their specific gravity. Gold, for example, has probably floated up volcanically. In Nevada, many of the gold mine are ancient volcanos, which came up from the interior of the Earth. Concentrations of other more important metals like tungsten are likely to be found in the center of the Earth and other planets.

On Earth, the deposits of these minerals near to the surface may eventually be exhausted. So the question is, where else could we get them? It is impossible to tunnel to the center of the Earth because of the extremely high pressure there—roughly 3.5 million atmospheres.

The situation is different on the Moon. The pressure at the center of the Moon is only about 100,000 atmospheres. Seismic measurements indicate that the Moon also has a core; and it, too, must have been molten at one point, because there are signs on the surface of a great deal of ancient volcanic activity. Thus, there are undoubtedly many heavy elements in the Moon's core, which could be retrieved. And we can drill a tunnel through the Moon, because, technologically, we can sustain the pressure of 100,000 atmospheres.

Drilling a tunnel through the Moon is not a trivial undertaking, nevertheless. We could not simply drill a mine and go down into it. On Earth, if we go down very deep in a mine and hit the wall with a hammer, the rocks that break off are shot into the mine shaft with the force and speed of a gun bullet. This happens because the deeper down we go in a mine, the larger the pressure gradient from the mine shaft into the rocks.

Is there a method by which we can tunnel to the center of the Moon and sustain pressures of 100,000 atmospheres? Yes: We can use nuclear explosions. First, we drill a mine shaft as deep as we can. At the bottom of the shaft, we place a large nuclear explosive and ignite it. The explosion crushes the rocks. The pressure gradient has been released, and we can continue drilling the mine shaft into the crushed rock until we again reach solid rock, where we set off another nuclear explosion. Proceeding in this manner, we will be able to reach the center of the Moon and extract the metals we need. And, as with chemical explosions, we can use nuclear shape charges to direct the explosion and very clean nuclear fuels to avoid contamination. We just have to hope that the environmentalists don't get there first and file a court case prohibiting our drilling.

We can do the same kind of mining on Mercury as on the Moon. The planet Mercury is very interesting, because of all the planets in our solar system, it has the highest specific gravity. That is an indication that Mercury must have valuable high-density metals in its interior. We could undoubtedly conduct similar excavations on Mercury, using 1,000 or possibly 1 million megaton explosions and creating craters through which we could drill deeper and deeper into the planet to obtain its metals.

The Martian Colony

Mars is a much more likely candidate for a large scientific and industrial colony than the Moon because it has water, which contains hydrogen, including the fusion fuel deuterium. But on Mars, water doesn't exist in the form of lakes or rivers, so we must come up with some other means of tapping it.

Nuclear energy is the solution to this problem, too. We can sink a shaft, place some fusion explosives in it, and ignite a very clean explosion with a particle beam, leaving no fission products. In this way, we can release the underground steam in a geyser to the surface, providing a water source for the colony.

Venus, unfortunately, is of little use, because its atmosphere and surface are too hot. We can visit Mercury, on the other hand, because it has no atmosphere. Mars is very cool, but we can always produce enough heat to sustain life—just a few hundred degrees is necessary. To heat a dwelling on Mars from minus 100 degrees Celsius to plus 100 degrees is very easy.

The same reasoning applies to the outer planets. Of course, we cannot land on Jupiter or Saturn, because the gravity is too great. But these planets have moons, and the moons are comparable in size to Mercury—much larger than the Earth's Moon. Two very interesting can­didates for colonization are Titan and Dione, moons of Saturn that were recently photographed by Voyager 1.

ABOVE TOP: View of uninhabitable Venus taken from 450,000 miles by Mariner 10 in 1974. The blue appearance is the result of darkroom processing to enhance the ultraviolet markings on the planet's clouds. ABOVE BOTTOM: Clouds covering Saturn's satellite Titan, seen in true color in this Voyager I photo. Titan may be inhabitable.

prospect opened up by fusion propulsion is nothing less than the industrialization and colonization of the solar system. Man of the Stone Age knew only the environment around his cave. Man of the Middle Ages could look out on his fields or his lord's castle, but his view was bounded by the horizon. But when the deep-sea vessel was invented at the end of the Middle Ages, along with clear glass that was the foundation for astronomy, man's horizon steadily broadened. And when I was a child, the idea of going to America was still considered a very big event. One had to take a boat on a lone trip. Today we jet from one continent to the other in a matter of hours. We are now planetary man. The man of the next century, however, will be man of the solar system. There are even certain recreational aspects of this. Mars has a canyon bigger than the Grand Canyon, so big it would extend from Arizona to New York, and a volcano much higher than anything on Earth. So as far as its scenery is concerned, Mars is a lot more interesting than Earth.

Olympus Mons, a spectacular Martian volcano, is one of the potential tourist attractions of a colonized Mars.

Colonizing the Entire Galaxy

We may leave the solar system, too. A study was done some years ago by the British Interplanetary Society on using a fusion propulsion system for interstellar spaceflight. Unfortunately, this kind of propulsion system is not as powerful as we would like, and it would take about 50 years to reach a nearby star using it.

But it is conceivable that in a few hundred years from now—or less— we could make interstellar spaceflights by building a spaceship as big as New York City with all the comforts of civilization and propelling it to another solar system (Figure 4). Once there, we would set up a colony on a planet that has Earth-like conditions. We would send unmanned probes or explorer craft ahead of us to tell us that such a planet was there.

Then, I propose the following scenario: The distance between solar systems is about 10 light years, and a fusion craft would take perhaps 50 years to arrive at the next one. Suppose man migrates into the galaxy and travels from the first solar system in all directions to neighboring suns, taking 50 to 100 years to arrive at each. Man remains in each new solar system about 1,000 years, building up a new technological civilization. Then he would move on to the next solar system.

If we propagate about 10 light years each 1,000 years, then we would spread with a migration velocity of one-hundredth of the velocity of light. Since the galaxy has a diameter of 100,000 light years, that means that in 10 million years, man will have colonized the entire galaxy.

Now, the galaxy is approximately 10 billion years old. Our solar system is about 4 to 5 billion years old, and the oldest, "population one" stars like our Sun containing heavy elements are about twice as old. Ten million years is a very short time compared with the age of the galaxy. There has thus been plenty of time for an advanced technological civilization to spread throughout the galaxy.

Why then has nobody arrived here? All that was needed in this conservative scenario is 10 million years. My answer to this paradox is that we are unique, at least in our galaxy.

Remember that nature always works with enormous amounts of things; nature works with abundance, producing more seeds than are needed. Suppose in every 10 galaxies, there is one technological civilization. Since there are something like 100 billion galaxies, there would be 10 billion coexisting technological civilizations. That there would be more than one technological civilization coexisting in one galaxy would be an exception.

Not only on Earth, but in our solar system, we are definitely unique. The Moon is too small to hold an atmosphere, although it is approximately the right distance from the Sun—virtually the same as Earth. Venus is large enough, approximately the same size as the Earth, but it is too close to the Sun. Radar pictures indicate that it was once like the Earth; it had continents, but then it lost its oceans. Mars is too far away from the Sun for life to evolve—it's too cold.

Thus, there was a very narrow band where life could have evolved. When the Earth evolved, it had a huge land mass in a large ocean. Suppose there was a planet in which there was a small ocean and a huge land mass. There would be much less water, and most of the land would be desert. Then evolution would take not 2 billion years as on Earth, but perhaps 20 billion years. But since the galaxy is only 10 billion years old, the evolution would still be in its first stage. For intelligent life to evolve on a planet in less than 5 billion years, the planet must have favorable conditions.

I think that the Earth-Moon system—which is in effect a double-planet system, because the Moon is not much smaller than Mercury—may have something very important to do with why we are unique. First, given the Earth's correct distance from the Sun, the Earth's ending up with a very large land mass could very well have happened when the Moon was captured. The capturing of the Moon was a very rare event. The only reasonable theory of how the Earth-Moon system came into being says that the Earth captured the Moon. This is the best theory because the chemical composition of the Moon is quite different from that of the Earth.

The capturing must have taken place in an encounter close to the distance that astronomers call the Roche limit. At this distance tidal friction forces are very large. If the Earth-Moon encounter had taken place at a larger distance, there couldn't have been a capture. In the asteroid belt, planets collided. Here we had a close encounter that led to a capture. And that capture probably created the supercontinent Pangea that was essential for the development of intelligent life. (Pangea is Wegner's ancient supercontinent, from which all the present-day continents were created by continental drift.)

Without the capture of the moon, Pangea may not have formed and everything would have remained under water. On such a planet there could never be intelligent life. Consider also the tides. The tides, caused by the Moon, forced the life in the sea to move onto land much more quickly.

Thinking about the extremely rare conditions that exist on Earth makes one aware of how unique intelligent life on Earth is. If we could persuade political leaders to appreciate this fact—that there is no other life like Earth's in the entire galaxy—perhaps they would take greater responsibility for making political decisions.

Dr. Friedwardt Winterberg, a pioneer in inertial-con-finement fusion, is considered the father of impact fusion for his early work in thermonuclear ignition by hypervel-ocity impact. Now a research professor at the Desert Research Institute of the University of Nevada System, he has long been at the forefront of research on the use of nuclear energy for spaceflight. Winterberg received the 7979 Hermann Oberth gold medal of the Hermann Ob-erth-Wernher von Braun International Space Flight Foundation for his work on thermonuclear propulsion.

This article is adapted from his speech at a conference on ^industrialization sponsored by the Fusion Energy Foundation in Los Angeles Oct. 15, 1980.