Rover—the Nuclear Way to Space

June 1, 1961

In one respect the nuclear rocket is unique among technical projects—in its essentials it is unanimously supported by both the scientific and engineering communities.

Most experts not only refrain from criticizing the Rover-type nuclear rocket (Rover itself is now a NASA-AEC project), but the vast majority consider it to be the cornerstone of a successful space program. There are virtually no dissenters. Liquid-propellant rocket enthusiasts, solid-rocket proponents, airframe manufacturers, space-medicine specialists, and civil and military space planners have all pressed for the earliest possible construction of a flyable nuclear rocket. Nowhere else in the myriad of space vehicle and pro­pulsion schemes can there be found such unanimity of approval.

There is a compelling technical reason for this sup­port. It is simply impossible to argue that nuclear rockets are not the best and cheapest means of per­forming any space mission involving large payloads. By contrast, opponents could argue with at least some effect against other nuclear-propulsion programs—in­cluding the nuclear plane. Many space missions, such as manned voyages to the planets, cannot be rationally considered without planning on the use of nuclear rockets.

The most elementary nuclear systems will carry two to four times the payload of the best chemical-fueled machines, given the same launch weight for both. If a fixed-weight payload is considered, the use of nu­clear rockets will materially reduce the size and the number of stages required for a space vehicle.

For example, it would require a six-stage vehicle with 10.5 million pounds of thrust in the booster to put a 15,000-pound payload on the moon and return it to the earth. If one nuclear stage were used in the vehicle, its booster would only have to produce 4.5 million pounds of thrust, and only five stages would be needed. If two nuclear stages could be used, the booster thrust could be reduced to three million pounds, and the vehicle would need only four stages.

No one contends, it must be noted, that developing an operational nuclear rocket will be easy or that it can be ready to go in much less than seven years after an all-out development program is initiated. However, some of the most distinguished scientists in the Atomic Energy Commission regard the development of the Rover-type nuclear rocket as an “enormously” easier task than the construction of either the atomic or the hydrogen bomb. This opinion was expressed over three years ago by Dr. Stanislaus Ulam, who with Dr. Edward Teller is regarded as a prime figure in the development of the hydrogen bomb, and by Dr. Norris Bradbury, Director of the Los Alamos Scientific Lab­oratory, in testimony before the Congress.

In January of 1958, Dr. Bradbury told the joint Committee on Atomic Energy that “the obstacles to be overcome in the first atomic and the hydrogen bomb seem now to be very large compared to the obstacles one has to overcome in going about nuclear propulsion [the nuclear rocket] and ramjet.” Dr. Ulam concurred at the same hearing.

The top-priority Manhattan Project to produce the A-bomb began shortly after Pearl Harbor. It was pur­sued with the greatest urgency because a handful of nuclear physicists believed that its early success was vital to the safety of the United States. They were able to convince the Administration that they were correct.

The first bomb was exploded in July 1945 after about three and a half years of all-out effort costing about $2 billion. Hundreds of millions of dollars were spent to provide the necessary experimental and pro­duction facilities for a minimum-length program. Over­all, some five and a half or six years had actually been required to build the bomb. A considerable amount of basic work on the bomb principles was done from 1939 through 1941 after Nils Bohr came to the United States with news of the first fission of uranium in Germany in 1939.

In contrast, the nuclear-rocket program was set up six years ago and has been operating on an extremely limited budget. Less than $150 million has been spent during the entire period. Many more than a handful of nuclear physicists and other scientists and engineers believe that the nuclear rocket could be as decisive in the exploration of space as the atom bomb was in World War II. Yet no one has been able to convince any Administration or its scientific advisers that it should have a high priority.

It is pretty well agreed that it would take $2 or $3 billion spent in a period of about five years to develop and flight-test the nuclear rocket. This price tag ap­parently has kept the brakes on the program even though in 1958 the Eisenhower Administration pub­licly began acknowledging a serious lag in US rocket booster power relative to the Soviets. Eisenhower offi­cials counted on the Saturn booster to put us ahead of the Russians.

President Kennedy has other ideas on Saturn. In a press conference, he said that it is “several years be­hind the Soviet Union,” and that, “regardless of how much we spend on the Saturn, we are still going to be behind.” He added that the rocket “does not offer any hope of being first to the moon.”

The Kennedy Administration, accordingly, is seeking a new engine system to surpass the Soviets. But, per­haps surprisingly, no concrete move has been made to accelerate the nuclear rocket. The Eisenhower appro­priations requests for the next fiscal year have been raised some, but the minimum requests of the project managers still have not been met. The sums of money in contention are very small. For instance, $15 million requested for the construction of another engine test stand and remote disassembly building was ruled against by the Kennedy Budget Bureau. It has been esti­mated that the loss of these facilities will delay the first flight of a nuclear rocket one year beyond the currently planned date of 1966 or 1967.

At this writing the Administration is still reviewing Project Rover amid growing criticism from the Demo­cratic Congress. Rep. Melvin Price of Illinois, Chair­man of the Joint Congressional Atomic Energy Sub­committee on Research, has said, “The lip service we are providing for the nuclear-rocket program, the target dates and long-range program statements being established regularly, are in reality steps to provide a decent burial for the nuclear-rocket program.”

Mr. Price has also described what he regards as close parallels between the stretchouts endured by the nu­clear-airplane program and the recent history of Proj­ect Rover. The Kennedy Administration canceled the nuclear-airplane program shortly after taking office.

Other congressional leaders are withholding com­ment until they see what national goals are established after completion of a long-range study of the space problem being conducted by President Kennedy’s advisers.

Regardless of the future actions of any branch of the government, it seems possible to sum up the current nuclear-rocket situation with two comments. First: No informed individual in the United States would want to be second in developing a reliable nuclear rocket. Second: It seems highly unlikely that the Soviets have spent less than the ruble equivalent of $150 million on nuclear-rocket development in the last six years.

The first nuclear-rocket proposals were made to the government in the middle 1940s. By 1955 the AEC-funded scientific laboratories at Los Alamos and Liver­more had small groups of scientists studying nuclear rockets and ramjets on a regular basis. This work depended to a great extent on the high-temperature material, heat-exchanger, and reactor physics research being accomplished under the aircraft nuclear propul­sion program.

About September of 1955 the AEC asked the De­partment of Defense about their interest in forming a specific nuclear-rocket research program. DoD showed intense interest in such a project—as long as it did not interfere with weapon programs going on at Los Alamos and Livermore.

The Air Force was made the cognizant service. It immediately joined with the AEC to form Project Rover with the object of proving the feasibility of nuclear-rocket engines through ground operation of such a device by 1959. Flight tests were envisioned by 1965. Development of the reactor for this engine was the responsibility of the AEC under the existing laws. Other portions of the rocket, such as the nozzle and turbopump, were managed by the Air Force.

First delay in the program came about a year later when Charles E. Wilson, then Secretary of Defense, overruled some of his own advisers and asked Louis Strauss, then AEC Chairman, to slow Project Rover down. Wilson’s letter to Strauss contained the follow­ing statements: “Careful study of . . . [the nuclear-rocket program] leads me to the conclusion that the dates suggested for the demonstration of reactor feasi­bility and flight tests are not realistic. . . . At my spe­cific request, can the AEC continue on a moderate scale to develop a reactor suitable for nuclear propul­sion of missiles, satellites, and the like?”

The technical people working on the program agreed that their original predictions had been optimistic, but only by about one year. They still believed in 1956 that feasibility could be proved by early 1960. To com­ply with the spirit of Wilson’s request, however, the level of effort was reduced at the AEC. Feasibility date was put forward to 1962. No further plans were made for flight testing.

Enough work had been done by the beginning of 1958 to convince Dr. Ulam, Dr. Bradbury, and many others familiar with the program that the nuclear rocket was feasible. At that time, however, there was reason for these opinions to be questioned. The first Rover experimental reactor, the Kiwi-A, had never been tested, and its operating temperatures were much higher than any ever attained. Then, a year later, in 1959, came the first tests. Any doubts about their suc­cess were dispelled in March 1960 when Dr. R. E. Schreiber, technical head of the AEC’s portion of Proj­ect Rover, told Congress that the “. . . use of heat-exchanger nuclear engines [Rover rockets] to propel space vehicles seems to be a matter of detailed engi­neering, money, and a determination to carry through such a project.” Since that time two more Rover reactors—Kiwi-A prime and Kiwi-A3—have been tested successfully to further strengthen Dr. Schrieber’s opinion.

The Rover management setup was altered in the summer of 1958 when the Air Force responsibility in the project was transferred to the National Aero­nautics and Space Administration. Dr. Hugh Dryden, Deputy Administrator of NASA, has stated that the nuclear rocket is his agency’s most important advanced propulsion program. This has not done much good as far as speeding the program is concerned. Congres­sional testimony has revealed every year that requests for Rover funds have been cut both in the AEC and the Budget Bureau.

This same pattern has been repeated by the Kennedy Administration. Total Rover appropriations requests for the AEC and NASA during the next fiscal year were $45.5 million by the Eisenhower government. The new Kennedy Administration added $14 million to this sum, but it was still $30.5 million short of the amount estimated by the project managers to be necessary if the first flight-test engine is to be ready by 1966-67.

It will, in fact, be impossible to sustain the Rover program at this funding level any longer. The funda­mental research portion of Rover is just about over. Engine development, which means bigger money, must commence if the program is to be kept on the rails.

The NASA-AEC Space Nuclear Propulsion Office, which manages Project Rover, is now reviewing pro­posals by seven groups of companies to select a con­tractor team for the first flyable nuclear rocket. This will be the Nerva engine. The name derives from the words “Nuclear Engine for Rocket Vehicle Applica­tion.” Announcement of the Nerva contractor is due about the first of July.

Large sums of money will be necessary to sustain this development program. It undoubtedly will be more costly than a chemical-engine development. Many ground firings of nuclear rockets will have to take place before the first one is flown. Heavy expenditures will have to begin in fiscal 1963, the first budgetary year completely within the province of the Kennedy Administration. Most of the criticism from Congress, such as that from Representative Price, stems from a seeming reluctance to begin these large expenditures.

Project Rover planners envision a sizable series of nuclear-rocket engines growing out of their present work. Fundamentally all of the engines in the series would operate in the same manner. They would em­ploy a solid-fuel reactor about the size of a large gar­bage can with parallel holes running through it length­wise. Hydrogen gas would be pumped through these holes to carry away the heat generated by the nuclear fuel. The hot hydrogen would then be exhausted out of a nozzle to provide thrust.

This basically simple scheme is complicated by the fact that the nuclear-fuel elements must be as hot as the hydrogen gas which produces the thrust. Appar­ently a temperature of about 3,500 to 4,000 degrees Fahrenheit will be possible using materials developed in the Rover program. Exhaust gases from the best chemical rockets are in this temperature range, but the chemical engine has a tremendous advantage. Its walls can be cooled to relatively low temperatures with films of propellant and by various other means. The nuclear-fuel elements must be as hot as the gas they heat.

The fine performance of the nuclear rocket compared to the chemical rocket is therefore not a result of higher gas temperature. It is gained by using hydrogen propellant. Hydrogen’s molecular weight is only about one-third the molecular weight of the exhaust gases generated by the combustion of the best combination of chemical propellants. Theoretically this means that at a given exhaust temperature one pound of hydrogen can produce three times as much thrust as one pound of the best chemical propellants. This thrust advantage can be translated into a greater payload-lifting capa­bility. Or, if the payload is held constant, the nuclear rocket can propel it to much greater distances from the earth than the chemical rocket.

Proof that this type of nuclear rocket is feasible was gathered during the three Kiwi tests. Graphite-loaded uranium was found to be a satisfactory fuel element material. Adequate means were found to support these brittle plates against the high-pressure loads created by the flow of hydrogen through the reactor. The fundamental concepts were established for a flight-type control system for the nuclear rocket.

A series of Kiwi-B tests will be made later this year to evaluate engines which come closer to the designs needed for flight. The main objectives of these tests are to use a flight-type propellant feed system and a flight-test type of nozzle cooled by hydrogen.

A series of Rover engines will be required for three reasons. First, a restart capability will be needed for certain space missions. This probably can’t be achieved with the first nuclear rocket. Second, it is anticipated that engine design can be improved significantly through flight experience. Third, engines of different thrust levels will be required.

Current plans call for the first nuclear rockets to produce several thousand megawatts of power. This translates into thrust at the rate of about fifty pounds per megawatt. Large reactors producing tens of thou­sands of megawatts, which could be used in single-stage rockets to boost very large payloads off the earth, undoubtedly will not be developed until small reactors have been flown successfully.

NASA is studying a method to get around the power Imitation of the early nuclear rockets and to provide a means of varying the thrust produced by any reactor. Basically this method is to increase thrust by adding chemical power to the nuclear rocket system rather than by increasing reactor power.

The most efficient and practical way of doing this is to burn a mixture of liquid hydrogen and liquid oxygen in the hot steam of hydrogen leaving the reactor.

This is analogous to providing the nuclear rocket with an afterburner. It appears possible to increase thrust fifteen times or more by this method.

Two penalties must be paid for the thrust increase. One is a loss in specific impulse. However, since aug­mentation would be needed only over a relatively small portion of any trajectory, this loss probably would not lead to a major reduction in over-all mission performance. The other penalty is that either added nozzle area or a large increase in operating pressure is needed during augmentation. Reactor strength limi­tations probably would rule out raising the operating pressure. Two possible schemes for varying nozzle area are shown on pages 38 and 39.

The afterburner idea makes it possible to consider using nuclear rockets as boosters during the 1960s and firing them from launch pads on the ground. A great deal of study has gone into determining the relative safety of this type of launch vs. starting nuclear rockets in space after they have been put into safe orbit by chemical engines. Most Project Rover people appar­ently feel that ground launches would not create an uncontrollable hazard although there has been much comment outside of the project favoring orbital start.

Most important point in support of the ground launch is that the reactor is clean when it starts and has no radioactive fission products. In case it crashes to the ground before it reaches orbit, its total power production has been low, and its accumulation of fis­sion products is much lower than that from the small­est weapons ever tested.

Heavy neutron and gamma-ray production as the rocket lifted off probably would make the launch stand and surrounding area within the radius of a mile “hot” for a few weeks. To overcome this problem and still have the use of vital and expensive range instrumenta­tion, Texas tower launch stands probably will be built at sea down the Atlantic Missile Range beginning a few miles offshore from Cape Canaveral. During in-flight aborts, reactors probably will be destroyed by flushing out with flourine or other strong oxidizers and/or blown apart by explosives. All reactors, whether they had been started or not, would receive this treat­ment.—End