Project Rover was an American project to develop a nuclear thermal rocket. The program ran at the Los Alamos Scientific Laboratory from 1955 through 1972 and involved the Atomic Energy Commission, and NASA. The project was managed by the Space Nuclear Propulsion Office.
Nuclear reactors for the Rover program were built at the Lab's Technical Area 18 (TA-18), also known as Pajarito Site. The reactors were tested at very low power and subsequently shipped to Jackass Flats at the Nevada Test Site. Testing of fuel elements and other materials science was done by N-Division in Los Alamos at TA-46 using various ovens and later the Nuclear Furnace. Parallel fuel rod development took place off-site at Rocky Flats.
Project Rover could be divided into three phases: Kiwi, between 1955 and 1964, Phoebus, taking place between 1964 and 1969, and Pewee, taking place between 1969 and the project's cancellation along with the cancellation of the NERVA rocket at the end of 1972. Kiwi and Phoebus were large reactors; Pewee 1 and Pewee 2 were much smaller and they conformed to the smaller budget available after 1968. Both Kiwi and Phoebus became part of the NERVA program.
As early as 1942, Enrico Fermi and his colleagues in the Manhattan Project discussed the use of nuclear energy to propel aircraft. In 1945, at the suggestion of Manhattan Project participants, the Air Force Scientific Advisory Board (SAB) studied the potential use of nuclear power for rocket propulsion. SAB recommended no action from this study.
In 1944, in the later days of Project Manhattan District, Stanislaw Ulam and Frederic de Hoffman published speculative ideas regarding alternate applications of nuclear energy. These ideas included the possible use of bombs to push missiles. At about the same time, T.F. Dixon and H.P. Yockey at North American Aviation published a paper discussing the use of a nuclear-powered heat exchanger to heat hydrogen or methane, concluding that nuclear power was sufficiently promising to deserve some investigation.
Two years later, in July 1946, a short paper was published by R. Serber of Project RAND surveying possible methods for obtaining thrust for a nuclear-powered rocket, including emission of fission fragments, beta and alpha particle momentum and mechanical heating. Serber concluded that using a reactor to heat particles of low mass was probably the most practical approach, although the problems of heat transfer and high temperatures would have to be solved.
The following year, in January 1947, a group of researchers at Johns Hopkins University published a much more complete survey of methods for the development of nuclear aircraft and rockets. They concluded that graphite and carbide would be good materials for this purpose because of their high melting points and compatibility with nuclear reactors.
Also in 1947, North American Aviation's Aerophysics Laboratory published a large paper surveying many of the problems involved in using nuclear reactors to power airplanes and rockets. The study was specifically aimed at a vehicle with a range of 10,000 miles and a payload of 8,000 pounds, and covered turbopumps, structure, tankage, aerodynamics and reactor structural design for that specific mission. They concluded that hydrogen was best as a propellant, and graphite would be the best reactor material, but they assumed an operating temperature of 5700 degrees F, at that time a temperature somewhat beyond the capabilities of available materials. North American's researchers had no knowledge of the Manhattan Project or its data and were not a part of the Nuclear Energy for Propulsion of Aircraft (NEPA) program being funded by the Air Force at Oak Ridge. Their work used very conservative numbers and emerged with very unpromising results for the idea of nuclear-powered rockets.
NEPA had been formed in 1946 and continued through the spring of 1951 under Fairchild's guidance. It studied nuclear rockets for about three years, from 1946 to 1949 and did the same for nuclear aircraft until the program ended.
An important series of articles in the Journal of the British Interplanetary Society entitled "The Atomic Rocket" was published in 1948 and 1949 by L.R. Shepherd and A.V. Cleaver. Beyond being a fairly complete survey of issues, methods and materials, this series was unclassified, finally making the topic available to the general public. The conclusion of the series was that nuclear power would be coming to the field of rocketry.
In 1952, Robert Bussard joined the Oak Ridge National Laboratory Aircraft Nuclear Propulsion program. Bussard commented that it was the first time he had ever witnessed a program that was three years behind the press clippings. General morale was low; the missile and rocket people understood and preferred chemicals, and the reactor people had no regard for the idea of flight. Bussard decided to write another survey, one with rigor as a major goal. He used data and analyses from existing chemical rockets, along with specifications for existing components. All calculations were based on what was known concerning nuclear reactors at that time. C.B. Mills, a well-known reactor physicist, lent credibility to the paper, as did A.B. Longyear of Aerojet General Corporation. Most importantly, Bussard's paper did not limit itself to a specific payload or range, but rather surveyed several ranges and payload sizes. In his paper, "Nuclear Energy for Rocket Propulsion", Bussard stated that the use of nuclear propulsion in rockets “is not limited by considerations of combustion energy” and thus “low molecular weight propellants such as pure hydrogen may be used.” He found that, while a combustion propulsion engine would produce “an exhaust velocity of 8300 ft/sec,” a hydrogen-fueled nuclear engine would “attain an exhaust velocity of 22,700 ft/sec at the same conditions.” Bussard’s proposal called for “a compact reactor built of graphite, which withstands high temperatures and actually gains strength when heated.” His study concluded that the “use of hydrogenous propellants necessitated protective coating materials,” which meant that if they were to use hydrogen as rocket fuel, then they would need to coat the reactor with certain materials. The study was published in the classified Journal of Reactor Science and Technology in December 1953.
Eugene Wigner and Jon von Neumann at Princeton University read the paper and expressed interest to the U.S. Air Force and the Atomic Energy Commission Reactors Branch. The Air Force asked the Los Alamos Scientific Laboratory (LASL), the Oak Ridge National Laboratory and the Lawrence Livermore Laboratory to review the field and report their conclusions to the Nuclear Missiles Subcommittee of the U.S. Air Force Scientific Advisory Board at its first meeting in Washington, D.C. in October 1954. The Condor Committee was formed at Los Alamos to consider possibilities for nuclear rocket propulsion. The group included Tom Gittings, Don McMillan, Phil Hammond, Phil Bendt, Lee Aamodt, George Bell, Jim Tuck and Conrad Longmire under the direction of Darol Froman, the director of LASL's K-Division (power reactors). At the October meeting in Washington, a decision was made to study the problem for another six months.
In February 1955, Tom Gittings proposed to Bussard that they investigate the possibility of boosting the nuclear ICBM to high altitude using atmospheric air. The idea was modified later to use a first stage booster such as the Navajo missile. It reduced the rocket mass by a factor of five.
The results were sufficiently promising that Lab Director Norris Bradbury formed a new Nuclear Propulsion Division to carry out research and development on materials and new reactor design work, with Raemer Schreiber at its head. Herbert York established a similar division at Livermore. In June 1955, Bussard moved to Los Alamos and joined the Nuclear Propulsion Division. Project Rover had begun.
The first phase of Project Rover, Kiwi, was named after the small flightless bird. It consisted of a series of non-flyable test nuclear engines, with primary focus on improving the technology of hydrogen-cooled reactors. Between 1959 and 1964, a total of eight reactors were built and tested. After conclusion of these experiments in 1964, further efforts were concentrated towards larger and more powerful Phoebus reactors. Kiwi was considered successful proof that nuclear rockets could be considered not only feasible but highly reliable and advantageous for space travel.
Phoebus was Phase Two of Project Rover. The focus was placed on achieving more power than was possible with Kiwi units and maintaining the maximum power for ever longer duration. The work on Phoebus was started in 1963, with a total of 3 engines being built and tested between 1965 and 1968.
Phoebus A-1 was tested on July 25, 1965, at Jackass Flats. A second test occurred three years later. Both tests were considered highly successful.
Pewee became Phase Three of Project Rover. It was small, easy to test, and well-sized for unmanned scientific interplanetary missions or small nuclear "tugs".