One Researcher's Personal Account (11/26/88)
by Freeman Dyson
(From Adventures in Experimental Physics, Beta (1972), pp. 323-6)
In an article called "Death of a Project" [Science, 9 July 1965, Vol. 149, No. 3680, pp. 141-144], I describe the public and political history of Project Orion. I do not mention there the fact that we made bomb-propelled models that actually flew. Here I describe how the project looked from a personal point of view.
Ted Taylor began the project in 1958, inspired by the belief that a small group of people with imagination and daring could build nuclear space-vehicles much cheaper and enormously more capable than conventional multistage chemical rocket vehicles. He was enthusiastically supported by Fred de Hoffmann who was director of the General Atomic laboratory in La Jolla, California. I found Ted's technical concept convincing and joined the project in La Jolla when the total number of employees was three. I worked on it for fifteen months -- the most exciting and in many ways the happiest of my scientific life.
When I left the project in September 1959, the number of employees had risen to fifty; we had together solved to our satisfaction most of the basic problems of vehicle design, the technical feasibility of our concept had been clearly established, and the government had decided not to take us seriously. Wernher von Braun and his chemical rockets had won the battle for government support, and the pattern of the space program was set in a way that left no place for us.
In the early days of the project we were all amateurs. Everybody did a little of everything. There was no division of the staff into physicists and engineers. I particularly enjoyed being immersed in the ethos of engineering, which is very different from that of physics. A good physicist is a man with original ideas. A good engineer is a man who makes a design that works with as few original ideas as possible. There are no prima donnas in engineering. And for a physicist accustomed to the pressure of personal competition, it was refreshing to work in a genuinely collective endeavor. To prove our claims, there were four main jobs to be done.
First there were theoretical calculations of the interaction between a high-velocity stream of gas from a nuclear bomb and the massive pusher-plate which covered the bottom of the ship. These calculations involved many areas of physics: hydrodynamics, radiation transport, elasticity and chemistry. The crucial quantity to be calculated was the mass of material boiled off from the pusher-plate by each explosion. If this mass was less than a few milligrams per square centimeter, the ship could survive; otherwise not.
The second job was to observe experimentally the boiling off of material from small areas of plate exposed to gas jets driven by high explosives. The explosive jets were able to cover only part of the range of temperatures, pressures and durations that were of interest for the full-scale ship. But the experiments provided a detailed check of the theoretical calculations within the overlapping part of the range and gave us confidence that the theory had not overlooked anything essential.
The third job was to draw complete engineering designs of full-scale ships. Here the major problems were the shock-absorber system, coupling the pusher-plate to the rest of the structure, and the ejector system which had to throw out ton-sized bombs at a speed of a few hundred feet per second with a delivery rate of one or two per second. Contrary to our original expectations, the ejector system stretched the state of the engineer's art more severely than did the shock absorbers. But we arrived at several workable solutions to both problems.
Flying of Bomb-Propelled Ship Models
~ The fourth job was to build and fly model ships propelled by two-pound charges of chemical high explosive. The models were not true scale models, since no chemical explosive can approach the ratio of power to mass in a nuclear explosive. The purpose of the flying models was to demonstrate that a vehicle possessing in rudimentary form the same engineering components as a full-scale ship, including pusher-plate and shock absorbers and ejector system, could be made to function correctly. [The test system ejected two-pound charges of chemical explosives at a rate of five-per-second.]
The model flights were the most beautiful part of the whole project. We had a launch site on a hillside covered with flowering shrubs and cactus, overlooking the Pacific Ocean. We usually went out early on Saturday mornings to set up the model and were ready for the countdown about lunch time. I often wondered what the Saturday afternoon sailors on the ocean thought of us, when some weird-looking object rose briefly from the test stand and blew itself into a thousand pieces. I still keep in my desk drawer a bag of aluminum splinters which I collected after one of our test flights, to prove to myself that all these happy memories are not just dreams.
The last of our flights took place on November 12, 1959, a few weeks after I had left the project and returned to my more respectable scientific work at Princeton. Brian Dunne reported the event to me by letter:
"Wish you could have been with us to enjoy the Point Loma festivities last Saturday. The Hot Rod flew and flew and flew! We don't know how high yet. Six charges went off with unprecedented roar and precision. We think we have it all recorded with five movie cameras. The chute popped exactly on the summit and it floated down unscathed right in front of the blockhouse. We are planning a champagne party for Wednesday."
So ended the romantic days of Orion. When the government decided not to use nuclear propulsion for the main civilian space program, our project was turned over to the Air Force. The Air Force kept it alive for six more years, during which a great deal of excellent work was done, but there was no more brave talk of manned expeditions to Mars by 1965, and of sampling the rings of Saturn by 1970. What would have happened to us if the government had given full support to us in 1959, as it did to a similar bunch of amateurs in Los Alamos in 1943? Would we have achieved by now a cheap and rapid transportation system extending all over the Solar System? Or are we lucky to have our dreams intact?
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