I have been interested in interstellar flight my entire life. Even in my early career I was enamored with the concept.
The Hughes Fellowship program was designed to be a work-study program. I wasn't allowed to work 40 hours a week. I would go to UCLA and arrange my class schedule first, typically about 25 hours a week. I would then go to my Hughes boss and arrange my work schedule around the class schedule. My bosses didn't mind - since I came "free - the fellowship program paid my salary. This gave me plenty of free time, which I spent in the UCLA Library looking up new papers on interstellar flight, adding to the Interstellar Travel and Communication bibliography I had started. I tried to collect and read everything. I would correspond with the authors, sometimes giving them useful tips to improve their papers, sometimes telling them about another similar paper that they may not have been aware of. In the process I became known as a person with a broad and unbiased knowledge in the field of Interstellar Travel. I kept dreaming, however I would find a better way to travel to the stars than those I had read about in all the hundreds of papers in the bibliography.
The Hughes Program was designed to end in three years with the award of a Master's Degree in Engineering, and with the employee switching to full-time work. I knew, however, that as a physics major, I needed to continue my Graduate studies until I obtained my Ph.D. So, although I liked Hughes, I had the G. I. Bill to help support the family, and the University of Maryland was able to supply additional funds. When the Hughes Research Lab Directors heard that I had been accepted, they understood immediately. They knew how important the Ph.D. degree was to the career of a physicist. They arranged one of the first Hughes work-study Ph.D. Graduate Fellowships for me, and both I and the University of Maryland were pleased to accept.
When I arrived in Maryland in 1961, one of the first things I did, indicating my strong interest in the field, was to try to set up an "Interstellar Research Foundation", along the lines of the fairly successful Gravity Research foundation. It was not to be source of funds but a repository of knowledge. I was planning on holding an annual essay contest and maintaining a circulating library. I had already had many brain-storming sessions with Mr. Marty Willinski, when he and I were fellow worker-students at Hughes, and together we had come up with about 50 people who might be interested in sharing information.
I got a Post Office Box and a mailer program, and in April mailed out 50 Announcements, calling for efficient methods for interstellar travel which did not use rockets, and for efficient methods of interstellar communication. I didn't get many responses, so after a while I dropped that idea; the mailer is in my book of Bound Papers 1961-1962.
Things suddenly changed dramatically in my own personal thought. I invented my own way to go to the stars! In early 1961, Ted Maiman at the Hughes Labs and shown that he could make a visible laser. I had been working with Ted, earlier, to develop a microwave maser for use in radar, and had published a paper in 1959 on that. When I read in the newspaper, in Maryland, of the laser, I was interested to learn that the laser color was brighter than the sun. On earth, it is the only color that is. The other thing, that really struck me, was that the laser light does not spread.
And I knew right then that I had an idea for sending human beings to the stars.
I knew a lot about solar sails, and how, if you shine sunlight on them, the sunlight will push on the sail and make it go faster. Normal sunlight spreads out with distance, so after the solar sail has reached Jupiter, the sunlight is too weak to push well anymore. But if you can turn the sunlight into laser light, the laser beam will not spread. You can send on the laser light, and ride the laser beam all the way to the stars!
I wrote the idea up in an internal memo to the Lab Director in May 1961 - Ground-based Lasers for Propulsion in Space. I liked the idea so well that I spent the time to work out the numbers. I found that if you think big, the whole concept becomes more and more feasible. The larger the laser sail, the lower the laser light flux on the sail material - until it is only three to six times brighter than sunlight - and the sail can be made out of aluminum.
The laser sail in the Beamed Laser Propulsion system is the same as a solar sail, so no new engineering is involved in that part of the system. The laser part of the system should not be designed as a "cannon". Instead, it should be imbedded at the image point in a telescope-like structure that is designed to spread out the straight beam from the laser so that it always fills the full sail diameter.
If you send the laser light backward through this big telescope, and adjust the amount of beam spread with time, the beam will stay in a straight line for many lightyears without stopping. The real trick to making this work is to think big. Fortunately, because my basic structure was a solar sail designed to reflect sunlight, I was already used to sails more than a kilometer on a side. Since this was a tough interstellar mission that had to beam a long distance, I was not afraid to consider laser beam spreaders 10's of kilometers in diameter and laser sail collectors 100's of kilometers in diameter. I was able to find lots of combinations that would work, and choose those combinations with higher speed, less laser sail mass, less laser power, etc. Once I calculated those solid engineering numbers I knew I had invented something really significant.
The first publication I did of the idea was in a popular magazine - "Missiles and Rockets"-April 1962. The article, "Pluto - the Gateway to the Stars", was reprinted in "Science Digest" in 1962, and that established my claim to having invented the first interstellar vehicle that used known technology.
I still didn't have a good way to stop.
I continued on with my Ph.D., while still collecting new ideas on interstellar travel. In late 1964 I finished my thesis work and returned to Hughes. I invented the Rotating Gravity Gradiometer Mass Detector in 1964, and the ramifications of that dominated my time until 1975. The first time most aerospace engineers knew that I was active in interstellar travel thought was in 1967, when Eugene Mallove and I published the first Interstellar Bibliography; it was already 18 pages long.
In 1973 I had a visit from science fiction authors Larry Niven and Jerry Pournelle. I gave them a lengthy briefing on a lot of far-out physics. They took away a lot of ideas on miniature black holes, which they immediately turned into award-winning short stories. They also took away my idea of a laser-pushed lightsail. I had warned them that the light from the Sun was not strong enough to stop the sail, but, being science fiction writers, when they wrote Mote in God's Eye, they ignored my advice and pretended it would work.
In 1975 I was approached by a group of people who knew that I was interested in interstellar flight. They were staffers to the House Committee on Science and Technology of the US House of Representatives 19th congress. What the Committee was aiming for was a plan for a Future Space Program 1975. They asked me to contribute, along with many other people working on Earth-to-Orbit launch, Orbit-to-Orbit launch, mars Transit, and similar near-term topics. They wanted someone to look further out than that, so they asked me to come up with a National Space Program for Interstellar Exploration.
It is a lengthy document, published in its entirety in the Congressional Proceedings, and contains a large number of ideas for deep-space exploration and interstellar exploration. There are a number of ideas in there that were not in my original ideas, including ideas by other people on how to go about stopping; nobody at that time had any good idea how to go about stopping a laser-pushed lightsail.
That document, in 1975, seven years after the first publication of the "Bibliography of Interstellar Travel and communication" was a tour de force which summarized all the ideas that I had which I had not had a chance to publish nor a chance to work on to the point where they could be published. I spent a lot of time on that Report, and I think it was very valuable at the time. There were a number of ideas, including fusion. Still, the only way which could take a probe and send it to the nearest stars and do it with known and tested technology was laser-pushed lightsails; it was still the best idea.
Once I had published the idea of laser-pushed lightsails, I then proceeded to publish a number of popular articles on the concept. At the same time, I published the "Bibliography" in a number of different places, most importantly in the "Journal" of the British Interplanetary Society.
I also condensed the House Committee paper into a single article, called "Program for Interstellar Exploration" for the "Journal" of the BIS, which appeared in 1976.
In 1976, there were only five good ideas for interstellar propulsion: Atom bombs, Ram Jets, Fusion, Anti-Matter, and Laser Beams.
The Atom Bomb propulsion concept was a vehicle designed in 1960 by Freeman Dyson and Stanislaw Ulam; it was based on classified data that Dyson and others had been able to generate, and may in fact have been tested under atomic bomb conditions but we don't know that. The design consisted of a vehicle pushed to close the speed of light by atom bombs. This may sound ridiculous, but if you make the vehicle very large and very tough and the bombs very small, and explode the bombs not too far away, say 100 feet, the bombs will heat up the big vehicle pusher plate but will not melt or damage it, so the pusher plate can be used hundreds of thousands of times. The final vehicle design carried 45 tons of passengers and supplies, which is enough for a small city of 2 or 3 hundred people, and was comparably large. The total vehicle weight was 400 tons. It consisted of two-thirds tons of bombs or 300 tons of bombs, each bomb weighing about one ton. That was the world's supply of atom bombs and I can't think of a better way to get rid of them. It was designed to accelerate over one g for 10 days, by using up the bombs once every three seconds. It could reach 1/30 of the speed of light. At that speed it would take 130 years to get to Alpha Centauri, but the system would work; it could have been built back in the 1960's and fired off in the 1960's. It was designed to get there in a hurry, and it didn't have a way to stop. (The way to stop would be to divide the bombs in half, use half of them to get up to speed and the other half to slow down, making the total trip time 260 years.) I would call that a World Ship, but a workable World Ship. It was the best we had, and was good enough. However, we would like to get there faster.
Another idea that was in the article was called the Bussard Interstellar Ram Jet. It was designed as a very large fusion-powered vehicle which wouldn't carry its own fuel. Instead, it carried a scoop, which would somehow scoop hydrogen out of space, over an area of thousands of miles, pulling the hydrogen atoms into a central core and feeding them into a fusion engine of unknown design. The engine would convert the hydrogen into hot helium, and expel it out the rear. The beauty about the Ram Jet Concept is, that since it collects the fuel from space it never runs out of fuel. It can go through the entire galaxy, it can go through the entire universe, provided the scoop works. The faster it goes, the faster it collects fuel, and the faster it can go. It's a wonderful concept, except nobody knows how to build the fusion engine and nobody knows how to build the scoop. In fact, analysis of the scoop shows that it will not work. If it was made of magnetic fields, it would simply send the hydrogen atoms back rather than collecting them, so it doesn't do any collection at all. It's still a wonderful idea, but it's more of a dream than anything else.
The other propulsion technique which has had a lot of work put into it was a fusion rocket. Fusion reaction is much more energetic than atom bombs, and so it would be nice to have. But nobody has come up with controlled fusion even on the ground, so until we do that, fusion propulsion has no future, because we can't make it. It also would be a rocket, and so would have to carry its own fuel; therefore it is limited to the total amount of thrust it can obtain.
Also in that 1976 paper is the first mention of using anti-matter as a fuel. As rockets, they would require fuel, but anti-matter is so powerful that we find on analysis that you don't need much of it. For every ton of vehicle you would need about 4 tons of some kind of reaction mass for the anti-matter to heat. The total amount of anti-matter we will be talking about will be in kilograms, so its weight is nothing. If you want to do an easy job with an anti-matter rocket, you just use a small amount of anti-matter to heat up 4 tons of fuel. If you want to do a tough job, then you use more anti-matter to heat the fuel even hotter to get more thrust out of it. At the time of the 1976 paper, people were just beginning to be aware that you don't want to use half and half of anti-matter and matter.
The last concept, Laser Beam propulsion, I invented. The only thing that has happened since my first paper in 1961 is that, although I originally didn't think of a way to stop, a gentleman named Noram realized that once I had gotten that interstellar probe up to speed, and visited briefly the target star, I could stretch out long wires and charge them up, and then use the magnetic field out in space to turn the interstellar probe around and send it back to Earth. It was a great idea, and I had published it myself, however I had never connected it to possible use with the probe. So that was the state of the field in 1976.
In 1981, I finally invented an improvement to my one-way beamed power sail - a way to stop at the target star. I was starting work on my novel, Rocheworld. The basic theme of the book was to teach the reader that the world is not always round - and what it would be like to live on that world. I didn't care what propulsion system I would use to get to this strange new world. Fusion would have been OK. I would have liked to use my new laser-pushed lightsail concept, but I didn't have a way to stop. Then suddenly I thought of a way it could be done.
The idea was to divide the sail into two pieces. As the crew approached Rocheworld, a large ring-shaped portion of the sail would be cut loose, leaving the central portion carrying all the mass of the cargo and crew. The much larger ring sail would be designed to curve a little bit so that the laser light from Earth would bounce off the retro-ring and onto the backside of the crew sail. The strong laser beam from the large retrosail would counter the weak laser beam from Earth, and after a year or so, bring the crew sail to a stop at Rocheworld. That idea was published in the "Journal" of the British Interplanetary Society in 1984, as "Round Trip Interstellar Travel using Laser Pushed Light Sails", where you will find credit given to my novel for its technical contribution to the retrosail method of stopping.
It was a year later that I developed a microwave version of the beamed power sail.
That idea was based on a visit with Freeman Dyson. We were discussing the pros and cons of poking very small holes into lightsails, to lower their mass. If the holes were smaller than a wavelength of light, the reflectivity of the sail should not be drastically affected. He said he had a sail design that was really perforated. He went to his file cabinet, and brought out three sheets describing the idea for a microwave sail that had very large holes. His analysis had found that the larger the holes, the faster the mesh sail traveled. But he didn't know what to do with this idea. He could send a large sheet of chicken wire to the stars, but what could he do with it when it got there?
Fortunately, I was trained in microwave transmitters and receivers, retrodirective arrays, neural nets, image processing, etc., and was able to combine all of those ideas to give the microwave sail an intelligent capability to collect microwave power from Earth, then to process television images during the fly-through and send them back to the Earth. That was the start of the Ultra-light Interstellar Probe. I published that idea in 1985 as "Starwisp".
It is difficult in this field to come up with new ideas, so I made it my job to collect all the new ideas and once every 5 or 10 years to present a review of the status of interstellar travel. I did this in 1986, 1991, and again in 1996.
In the years since 1976, the Atomic Bomb-propelled rocket had developed no changes. The Fusion rocket had no changes. The Ram-Jet idea, remarkably, did have a change. Jackson suggested that instead of the ram-jet scooping up its fuel, which we were having difficulty doing, we drop the fusion system from the entire ram-jet concept, and just use the ram-jet collector. We could then beam power to the collector to heat up the scooped-up hydrogen, and that power could be lasers, anti-matter, or any technique for supplying power at a distance. The problem was, we still didn't know how to build the scoop. Maybe that idea will inspire someone else.
In the Anti-Matter division, increased knowledge and technical work revealed that the idea looked better and better. First of all, we had learned we should concentrate on the anti-protons, because once they annihilate, they produce particles that last a short time but travel a long distance. Most of the particles generated will travel 21 meters, or 60 feet. And if you wind up that distance, using a moderate magnetic field, you can build a big tank which will control and contain most of the particles. If you add hydrogen or water particles, they will interact with the fuel particles and heat up, converting something like 30% of the annihilation energy into workable thrust. Two other advances had been made in the last 10 years: both the USA and the USSR had spent a lot of time and money developing proton-beam factories, which produced anti-protons to be used in scientific experiments; at the same time, many atomic-physicists were working on dozens of ways to catch, contain, and trap hydrogen and other particles, which meant that they could do the same with anti-particles. Thus it was possible to show that making anti-protons is feasible; collecting them is difficult, but once collected and slowed down, they can be contained and used.
In the area of beamed power, a new concept came up called Pellet-pushed Propulsion. Instead of using atoms, it used physical pellets, sometimes even little tiny directed devices. That idea has had a lot of thought and calculation, but no one has taken it much farther.
In my 1996 review, I found that other people had also come up with new ideas for stopping a beamed-laser lightsail. One of them involved a magnetic sail.. After using the laser to get the sail up to speed, you dropped the sail and spread out a big loop of current-carrying super-conducting wire. The magnetic field from the current will push against the atmosphere of the star, and bring the probe to a halt. There is yet another way to do this, using a plasma wave.
Now that other people were solving the problem of stopping, more people were working on finding alternate ways to get to the stars. The Jet Propulsion Lab facility can now push a small interstellar probe partway to the stars, using a solar sail.
I finally realized I wouldn't see any progress on a true interstellar vehicle before my career was over, so I decided to switch to work on space tethers. So at age 70, I have turned over the field of interstellar travel to Geoffrey A. Landis.
I still maintain contact with everybody in the field; from 1961 to 1991, I was one of the pioneers and inventors in interstellar flight, and I am proud of the contributions I was able to make.
I was active in the aerospace field of smart structures from 1979 to 1985.
A "smart structure" is defined as an engineered mechanical structure built of integrated materials which can sense thermal, mechanical, elastic, and inertial loads; and which can apply forces and moments, when powered by control electronics, in such a manner as to adapt the geometric shape and dynamic response of the structure, based on a set of rules.
These complex mechanical structures usually start with composite-material -laminated bases, like carbon-carbon fiber. By inserting between the laminates things such as piezoelectric ceramic transducers, shape memory alloy wire actuators, passive viscoelastic dampers, temperature sensors, power control electronics, etc., the structure can be converted from merely a "stiff stick" into a flexible, adaptable, component part of a complex structure, such as a very lightweight telescope that is many times lighter than a standard space telescope, but with much better performance.
By proper design and operation you can obtain different elctromechanical properties out of the same "smart structure". The new piezoelectric ceramics along with new high-strength materials became a very powerful means for controlling the properties of a very large and massive structure.
The big change about during the Cold War. It started with the navy. They had a desire to make sonar more and more efficient, in terms of the coupling of electrical power in the piezoelectric ceramic transducer with the sound put into the water.
Tests on these transducers revealed that you could put a great deal of energy into the structure through them, and get a lot of the energy back out again, with almost no loss.
The Navy was able to get a high coupling of electrical power into sonar power. Now I had found that if a structure had any vibrations in it, small transducers could not only sense the vibrations, but "suck" the energy out of them. I became aware of this capability during my work on gravitational radiation detectors.
My Thesis/Dissertation Abstract in 1986 was: Vibration control of flexible structures using piezoelectric devices as sensors and actuators was analytically predicted and experimentally demonstrated.
For my thesis, I had used piezoelectric transducers to extract vibrational energy from a one-ton bar of aluminum. I should be able to apply the same techniques to the kilogram-sized mechanical struts in typical aerospace structures. I realized it was important for the war effort and for the control of aerospace designs that we start looking at the ultimate capabilities of these transducers. I had had a great deal of experience with them as stress elements, so my major contribution in this field was to write papers showing how powerful they could be in terms of putting energy into a structure and getting it out again.
I concentrated primarily on structures which had unwanted vibrations in them. If you are trying to build a lightweight aerospace structure which will be out in space and subjected to noise, you want to arrange it so that you can get that energy out and stop the structure from vibrating. I immediately began demonstrating to people at the Hughes Labs that it was possible to stop very heavy objects from vibrating, with a little slab of piezoelectric material.
Further, as I was extracting energy from a structure with these transducers, I learned that not only could they damp vibrations, they could cool it electronically. Essentially redoing my thesis, I demonstrated to the engineers that not only can you detect vibrations smaller than an atom, you can extract energy from them, and furthermore, you can measure them exactly. It was as I worked with the equipment for my thesis that I really got to know the potential of working with the single modes in the bar.
To show the seriousness of the work of these piezoelectric transducers, I spent some months on an effort which resulted in two papers, one on theory, the other on experiment. I had a theorist work with me, and he did such a beautiful job of analyzing what was going on that we decided he should be the primary author of the theory paper, and I was the primary author of the one on experimental results. The titles were "Electronic Damping of Orthogonal Bending Modes in a Cylindrical Mass", and C. J. Swigert was my associate. Both were published in 1981, in the "Journal of Spacecraft and Rockets". In this pair of papers, especially the experimental one, we show that we can take an antenna mast, designed to be used on the Pioneer Venus spacecraft, which had vibration problems, and stop it from vibrating.