« PreviousContinue »
Mr. FULTON of Pennsylvania. Thank you.
You are not recommending that, for the purpose of the gaseous-core study, any one of these other programs of NASA, such as solid-core development, Orion, or high-energy chemicals, be deprived of needed funds and transferred over into this program, are you?
Mr. McLAFFERTY. Our responsibility, we feel, is primarily to push for this program. But there is excellent work going on in many other fields, and the results of this work will be of great help to us in future
Mr. FULTON of Pennsylvania. So that if you get heat transfer work, nuclear calculations, high density hydrogen properties, as well as supporting research on metals, valves, nozzles, as we come up to this high level of thrust impulse, that the gaseous core will give us, that all goes really to help you on your program; doesn't it?
Mr. McLAFFERTY. What we have tried to do is to separate the problems which are now facing solid-core rockets from the unique problems which face gaseous nuclear rockets. All of the information we would generate in an expanded program would be related to gaseous nuclear rockets, and we would assume that the other work would still be carried on.
Mr. FULTON of Pennsylvania. What you are doing is simply stepping up the pressure and temperature in the area of reference? Mr. McLAFFERTY. The hydrogen densities we would consider are higher than the hydrogen densities that are being considered in the other programs. This gets a little bit into the area of classified information, but we are talking of higher pressures and higher densities than are now being considered in the solid-core program.
Mr. FULTON of Pennsylvania. I agree on that; it is a difference in the order of magnitude. My point is should we not be doing the research as we go up to this magnitude all along? We shouldn't skip any one of these other programs.
Mr. McLAFFERTY. Correct.
Mr. FULTON of Pennsylvania. Nor should we starve them, we should balance them out and, of course, that is an administrative function that is under Mr. Finger; is that not right?
Mr. McLAFFERTY. Correct.
Mr. FULTON of Pennsylvania. Thank you.
Mr. DADDARIO. Mr. Chairman.
Mr. TEAGUE. Mr. Daddario.
Mr. DADDARIO. I think Mr. McLafferty has made an excellent statement which is really what we expect from United Aircraft Corp., which by chance happens to be
Mr. TEAGUE. Mr. Daddario comes from Hartford, Conn.
Mr. DADDARIO. You said you think this program should be accelerated, and you have given some reasons as to why. I wonder as you look to the future and you fit into it the idea that you will havewe can develop through this process or another a single stage spaceship, what level of financing do you contemplate? What does the future look like in this particular area, what do we have to do, what should we prepare ourselves for from the standpoint of the financial stimulus needed to sustain the overall effort?
Mr. McLAFFERTY. This is a very difficult question to answer. The research program funding which we recommend is very modest compared to the funding required for a development program, but represents a vigorous effort compared to that of most research programs. When we get beyond the research stage, the rate of expenditure would go up in the same order of magnitude as that for solid-core nuclear rockets. It might be somewhat greater than that for solid-core nuclear rockets because many of the problems are more complicated. But, on the other hand, because we have so much inherent performance, we may be able to build structures, cases, and so on, without worrying about weight as much as is normally done in solid-core nuclear rockets and may be able to build things cheaper per pound.
Therefore, whether the costs are much greater, or somewhat less than for a solid-core nuclear rocket program, is almost impossible to answer right now. However, I think if you take the order of magnitude cost numbers that Mr. Harold Finger has talked about, you would come to about the right figure.
Mr. DADDARIO. Thank you, Mr. Chairman.
Mr. FULTON of Pennsylvania. One more question.
Mr. TEAGUE. Mr. Fulton.
Mr. FULTON of Pennsylvania. What period of time are you talking on successful development? How far in the future will this be, the gaseous-core rocket and the engine vehicle?
Mr. McLAFFERTY. The most intelligent thing I could say is that we don't really know.
Mr. FULTON of Pennsylvania. About 1990? I have heard that mentioned: is that correct?
Mr. McLAFFERTY. I would hope that it would be substantially before that. It is difficult to envision a gaseous nuclear rocket in flight within 10 years since it would take an awful lot of good fortune and an awful lot of funding to get it going in that time. But some time after 10 years the possibility of an operational gaseous nuclear rocket begins to rise, and if it is going to work at all, it should certainly work by 1990.
(The complete prepared statement of Mr. George H. McLafferty is as follows:)
[Report, UAR-C41, Mar. 17, 1964]
REVIEW OF THE Gaseous-CORE NUCLEAR ROCKET PROGRAM AT UNITED AIRCRAFT CORP. RESEARCH LABORATORIES, EAST HARTFORD, CONN.
Mr. Chairman and gentlemen, my name is George H. McLafferty. I am program manager for the gaseous-core nuclear rocket program which has been in progress at the Research Laboratories of United Aircraft Corp., during the past 5 years. I am pleased to have the opportunity to appear before this committee today, since it is our belief that the gaseous-core nuclear rocket offers a most unusual potential for economic space transportation in the future. It is particularly encouraging to us that this subcommittee has the foresight to review such advanced concepts as gaseous nuclear rockets at a time when so much emphasis is being placed on the more conservative and immediate objectives in space propulsion. It is our firm conviction that a balanced program directed toward the development of existing propulsion technologies for the fulfillment of immediate objectives, together with a program covering research in advanced technologies, is essential to the orderly growth of economic space transportation.
By way of introduction, the Research Laboratories of United Aircraft Corp., which I represent, are an autonomous unit of United Aircraft Corp., which operates as a central research organization in support of the technical activities of the six divisions of the corporation. Research in advanced propulsion, which is conducted to supplement the activities of the Pratt & Whitney Aircraft Division and the United Technology Center of United Aircraft Corp., is characterized by the investigation of systems and components having potential performance which represents a highly advanced state of the art. In the area of advanced rocket technology our primary efforts over the past 5 years have been concentrated on research directed toward the determination of the feasibility of the gaseous-core nuclear rocket.
Today I will discuss the motivations for the investigation of gaseous-core nuclear rockets, the principal problem areas associated with the development of this concept, and the need for expediting our national program in gaseous-core nuclear rocket technology. Because of security restrictions, only limited information regarding the progress which has been made to date under the United Aircraft Corp. program can be presented in this statement. To provide a realistic assessment of the state of the art relative to the feasibility of this concept, it is srongly recommended that such information be presented in executive session.
MOTIVATION FOR GASEOUS-CORE NUCLEAR ROCKETS
Our ultimate goal for manned space flight in the solar system is the singlestage spaceship which would have the capability of traveling from the earth to points in space and back to earth. Since such a vehicle could be used and reused, the economic advantage over current-generation multistage nonreuseable vehicles is readily apparent. As stated by Maxwell W. Hunter, Jr., in the February 1963 issue of Nucleonics magazine, "Only with the development of a spaceship of this simplicity, economy and versatility of operation can we foresee the economic feasibility of really large-scale manned space operations with whatever permanent manned bases on the moon or planets are necessary."
The attainment of single-stage space vehicles is critically dependent on the development of high-thrust propulsion systems having high values of specific impulse that is, pounds of thrust for each pound of propellant which is utilized every second. The most advanced chemical rockets have values of specific impulse approaching 500 seconds and solid-core nuclear rockets of the type currently being investigated under Project Rover have projected values of specific impulse approaching 1,000 seconds. The successful development of such solidcore nuclear rockets will have a profound influence on our future capabilities for economic space travel. However, the fulfillment of our ultimate goal for singlestage spacecraft will require the development of propulsion systems having values of the ratio of thrust to weight greater than unity and specific impulses considerably greater than those afforded by the solid-core nuclear rocket. By way of example, the Saturn V vehicle which will be used to place our astronauts on the moon will require a takeoff gross weight of approximately 6 million pounds to perform the mission and return the 8,000-pound command capsule to the earth's surface. The use of solid-core nuclear rockets for this mission would allow a return capsule weight of approximately 25,000 pounds for early engines and up to 70,000 pounds for more advanced engines. On the other hand, an advanced nuclear propulsion system with a thrust-to-weight ratio of 20 and a specific impulse of 2,500 seconds would permit the delivery of a 1-million-pound capsule back to earth for the same vehicle initial gross weight as for the chemical system. In the case of the nuclear rockets, it has been assumed that chemical rockets would be utilized to boost the vehicles outside the earth's atmosphere and thereby minimize nuclear radiation hazards. Although this complication reduces the payload relative to that which could be obtained using a true single-stage configuration, the resulting economic disadvantage is relatively slight.
DESCRIPTION OF GASEOUS-CORE NUCLEAR ROCKET CONCEPT
The attainment of values of specific impulse greater than that afforded by the solid-core nuclear rocket with hydrogen propellants is dependent on the degree to which the velocity of the expelled gas can be increased. Although it is possible to attain extremely high values of exhaust velocity by the electrostatic acceleration of charged particles, which is the principle of plasma and
ion electric rockets, the resulting ratio of thrust to the sum of engine and power supply weight is extremely low. The only means for increasing specific impulse while still retaining high values of the ratio of thrust to weight is to increase the exhaust velocity by increasing the gas temperature. Since the gas temperature in a solid-core nuclear rocket is necessarily limited by the structural characteristics of the fuel elements at elevated temperatures, it is apparent that further increases in temperature will require the containment of nuclear fuel in gaseous form.
In the concept of the gaseous-core nuclear rocket being investigated at United Aircraft Corp. Research Laboratories, energy from gaseous nuclear fuel located within a cavity is used to heat the propellant gas to very high temperatures. As shown in figure 1 these high-temperature gases are then expanded through
a nozzle to attain extremely high exit velocities and corresponding high values of specific impulse. For values of specific impulse between 1,500 and 3,000 seconds the corresponding average temperatures immediately upstream of the nozzle throat would be between 10,000° and 30,000° F. Since gas temperatures of this order of magnitude adjacent to the walls would cause rapid melting and boiling of the structural material, a relatively cool film of gas must be located between the hot gases and the wall.
An equally imposing problem which must be overcome to permit development of gaseous nuclear rockets is that of minimizing the loss of nuclear fuel from the cavity. Studies of nuclear criticality indicates that the amount of fuel which must be stored in the cavity varies from approximately 5 kilograms (11 pounds) to 20 kilograms (44 pounds) for engines having diameters between 8 and 25 feet. If this gaseous fuel is permitted to mix with the propellant, fuel loss rates approximately equal to the propellant flow rates would result. Because of the high cost of nuclear fuel (approximately $7,000 per pound) such a fuel loss rate would be intolerable.
The Research Laboratories of United Aircraft Corp. have been conducting theoretical and experimental investigations to develop flow configurations which will minimize the loss rate of nuclear fuel in full-scale engines. These investigations have concentrated on a particular flow configuration which counteracts many of the mechanisms which cause loss of fuel from gaseous nuclear rockets. The principle of operation of this flow configuration and the details of the flow patterns within the engine are classified.
Although the estimates of specific impulse and thrust-to-weight ratio for the specific engine configuration under investigation are also classified, generalized analyses to determine the performance potential of gaseous nuclear rockets have been available in the open literature for many years. These analyses indicate the possibility of values of specific impulse between 1,500 and 3,000 seconds and values of thrust-to-weight ratio considerably greater than unity. In addition, if secondary coolant loops can be used to transfer heat to space by means of a space radiator, values of specific impulse approaching 10,000 seconds may be possible. While hydrogen has been considered the natural propellant because of its low molecular weight, it is interesting that water, ammonia, and methane offer certain attractive advantages where overall vehicle system characteristics are considered.
CURRENT STATUS OF UNITED AIRCRAFT PROGRAM
Research in gaseous nuclear rockets was initiated in the research laboratories in 1959 under a corporate-sponsored program in advanced propulsion technologies. From 1961 to 1963 work was continued under two Air Force contracts totaling $1,150,000. Two contracts, totaling approximately $600,000 and scheduled for completion in September 1964, are now being carried out under sponsorship of the joint NASA/AEC Space Nuclear Propulsion Office. The first of these contracts was initiated in June 1963. The second was initiated in September 1963 following termination of the Air Force program as a consequence of a redirection of Air Force activities in nuclear propulsion technologies. United Aircraft Corp. has continued to supplement this effort with a total expenditure to date of approximately $800,000.
The technical effort under this program has been concentrated primarily on the imposing problems of fuel containment, wall cooling, and heat transfer from the fuel to the propellant. Under the fluid mechanics program, analytical and experimental investigations have been in progress to study the behavior of mixtures such as iodine and air, smoke and air, and dye in water to gain an insight into the mechanisms involved in the flow of gases into the reactor. Encouraging progress has been made in the containment of a simulated gaseous nuclear fuel under cold-flow conditions. An investigation of another approach to separate the fuel and propellant in the core has also been in progress under one of the two NASA contracts. These studies have been directed toward the determination of the spectral transmission properties of various transparent materials which might provide the needed separation of fuel and propellant without melting the transparent wall. In particular, attempts are being made to determine if the radiation damage to the transparent walls can be annealed out at an adequate rate by finding an operating temperature hot enough to remove the damage but not hot enough to sap the strength of the material.
Encouraging progress has also been made in the determination of heat transfer rates to the propellant and to the rocket structure. Unique concepts also have been evolved for cooling the nozzle component of the rocket with a minimum penalty in overall rocket performance. Although security restrictions prevent a detailed discussion of the progress which has been made to date in determining the feasibility of this gaseous-core nuclear rocket concept, it can be stated that no serious obstacles have been encountered which would discourage continued enthusiastic pursuit of this program.
On the basis of the encouraging progress which has been made to date and in consideration of the extreme performance potential of the gaseous-core nuclear rocket, it is strongly recommended that the current program be accelerated and amplified. In particular, additional efforts should be directed toward extending the present successes in experimental work to areas which more closely represent the conditions which are expected to exist in an actual rocket system. Following a 2- to 5-year period of such additional experiments, it is anticipated that sufficient technology will have been developed to permit consideration of tests of an actual rocket engine with gaseous nuclear fuel. A sketch of a facility which might be used in such tests is given in Fig. 2. In this test arrangement, water