James Dewar set out to the write the story of the nuclear rocket, and that’s exactly what he succeeded in doing. To the End of the Solar System is a nearly complete history of nuclear-thermal propulsion research from the discovery of radioactivity in the 1890s through the cancellation of the American research & development program in 1973. He discusses the work done in subsequent years, though through the book’s publication in 2004 that research was largely theoretical.1 Dewar consequently directs his attention to the period when nuclear propulsion was a near-term possibility.
It is not, primarily, a technical tale. The majority of the book focuses on the political, managerial, and bureaucratic aspects of the program. There is a good deal of technical detail, but ultimately the engineering challenges are not the biggest hurdle for those supporting nuclear propulsion. Securing long-term support and funding from industry and Congress will be much more difficult.
The book also necessarily focused on the American nuclear program, though addresses briefly Soviet work. Unfortunately, our knowledge of their program comes from only a handful of sources, sometimes contradicting one another. How much useful information we can glean from them is uncertain.
The Cold War played a major role in the development of the nuclear rocket, but the story begins well before the Russian Revolution. A number of early rocketry theorists, including Robert Goddard, Konstantin Tsiolkovsky, and Hermann Oberth speculated on using the energy released from radioactive decay to propel spacecraft, but both the quantity available and isotopic energy output was minute. Discussion remained entirely abstract and largely an aside in the development of rocket propulsion until after the Second World War.
The ultimate motivation was military. As atomic bombs grew larger and larger, existing aircraft and missile designs struggled to keep up. A handful of scientists floated nuclear options to deliver these weapons, either in aircraft, missile, or pulse-propulsion form. The Pentagon developed a nuclear airplane program as a joint venture between the Air Force and Atomic Energy Commission with the express goal of developing an aircraft capable of delivering a hydrogen bomb inside the Iron Curtain.
Oak Ridge National Laboratory hired a young physicist named Robert Bussard2 to work on the nuclear airplane project. Brussard did excellent work but insisted on studying nuclear rockets alongside his official duties. Through months of feverish lucubration, he developed some of the first viable nuclear rocket concepts. His classified publications attracted the interest of several prominent physicists. Teams formed at Los Alamos and Livermore National Laboratories to develop Bussard’s concepts. Los Alamos eventually came to favor nuclear turbojets, while Livermore concluded that nuclear rockets were more viable.
When Congress got involved a few years later, the need for nuclear aircraft or missiles was waning as bomb mass fell and chemical launcher capability grew. However, Washington was beginning to think about spaceflight, and decided to continue funding both programs. Ironically, the AEC assigned Los Alamos to study rockets and Livermore to study nuclear jet engines. These became Projects Rover and Pluto, respectively.
Los Alamos began constructing facilities at the Nevada Test Site to put their series of reactor designs through the paces. Each reactor was a hard-won concession from Congress, which was worried about just how many tests and iterations would be necessary to develop a viable system. Throughout the program, many in Washington opposed Project Rover or believed that it should be transferred to the civilian space program. NASA was very skeptical of the program, however, and so a small clique of Senators fought to keep it under AEC aegis. Ultimately NASA and the AEC found a reasonable compromise, forming a joint Space Nuclear Propulsion Office.
The early Space Race initially helped Rover’s prospects, as the Soviet Union sped ahead in missions and technological firsts. Nuclear propulsion would enable much more impressive projects, such as manned planetary landings, massive probes to the outer Solar System, space stations, and Lunar bases.
In Nevada, reactors were steadily improving. Their thrust and successful burn-time grew, though several failures occurred, including one which required an expensive clean-up effort. Through a series of redesigns, however, the test articles began to closely match the existing aerothermodynamic models. Better designs were coming, but a large question mark hovered over the program: when would Rover get a reactor in-flight test?
RIFT was well-named, as it became a political hot-button issue. Early concepts involved dumping the used reactor into the ocean or using it to perform orbital insertion as a Saturn upper stage. Both of these concepts were eventually abandoned on safety grounds, but did nothing to advance the issue in Congress.
Ultimately, nuclear rockets became a chicken-and-egg problem. Congress and NASA leadership did not want to approve a program that required nuclear propulsion until the technology was ready, but also hesitated to develop nuclear technology until a mission required it.
Much of the opposition stemmed from budgetary concerns. NASA was a rapidly-growing slice of the federal budget, competing with the Vietnam War and Great Society for a shrinking set of tax dollars. Recall that fiscal conservatism was once common in both political parties, rather than a fringe movement within one of them. Few wanted to commit to the large, expensive missions which nuclear propulsion would enable (such missions being prohibitively expensive—in the extreme—with chemical propulsion).
The concept of preeminence rapidly fell out of favor. Washington decided that Apollo would be the extent of trying to upshow the Soviet with big flashy projects. After Skylab, the Space Race would be abandoned in favor of developing the “economical” space transportation system. Los Alamos was still developing reactors, including the most powerful reactor ever run, but the tide was shifting towards smaller reactors to complete technology validation. Stacking small reactors, it was thought, would provide adequate thrust and cut down burn durations.
Even the space transportation system came under attack as tax revenue continued to shrink in the Nixon years. The original plan included nuclear orbital tugs, the chemical shuttle, and a space station. Ultimately, only the shuttle was funded, with the design of its cargo bay becoming a proxy battle over the future of nuclear propulsion. Small nuclear engines could be carried to orbit in the shuttle cargo bay, after which they would be attached to larger spacecraft and activated once astronauts had left the vicinity.
The Space Transportation System concept in 1970.
Source: Marshall Space Flight Center
Quite suddenly, though, all funding was terminated in 1973. Congressional funding was falling but still there, and researchers thought they were approaching flight test readiness. The change was ultimately a decision made by bureaucrats in the executive branch, which reprogrammed the funds without the consent of Congress or the President.
Believe it or not, this was technically a legal move. Several Senators were enraged by it, including Barry Goldwater—not exactly a friend of large, expensive federal programs. Within a few years, laws were introduced which required the Executive Branch to spend funds on the programs which Congress had allocated them for.
The defunding took the Soviets by surprise, to the point that they suspected it was a false-flag move to classify the work. Unfortunately, this does not appear to be the case. In fact, some of the officials involved in cancelling Rover were involved in the later Air Force Project Timberwind, which again attempted to develop nuclear propulsion. This too was cancelled after the end of the Cold War, without producing any real results.
All of this was really fascinating history, which I think should be discussed more widely in the spaceflight community. Nuclear propulsion, despite some extreme challenges, came very close to practicality. In the end, it was cancelled by politicians who failed to see the opportunities it provided rather than for the technological difficulties it faced.
It is quite arguable that Project Rover was well-worth the cost, and could have been justified on technology-development grounds alone. The program created entirely new industries, such as commercially-affordable cryogenics, and demonstrated all kinds of new material sciences. One would expect spaceflight advocates to mention this more often.
To the End of the Solar System does discuss the technical details, but is ultimately a political history. The style is somewhat confusing in this regard, routinely switching between Washington and Nevada—and not necessarily in chronological order. I would like to reread it to see if contextualization improves the narrative, but sadly it goes back to the school library tomorrow. Maybe one day I’ll buy a personal copy.
However, the appendices are worth reading. They provide a decent introduction to the major aspects of nuclear propulsion, without drowning the reader in technical minutiae. The discussion of radiation safety, for instance, was extremely informative and should allay many fears about the dangers of nuclear rocket testing. Dewar also dedicates a section to the Russian nuclear propulsion program. These are a good introduction to the subject, though hardly an expert make. I’ll be diving into dedicated nucleonics and advanced propulsion resources Soon™.
On the whole, To the End of the Solar System: The Story of the Nuclear Rocket is a rich resource for those studying the history of nuclear propulsion, whether for technical or non-technical reasons. Understanding the story of advanced propulsion is essential for those of us who wish to see humanity spread out into the Solar System, and James Dewar has written an excellent introduction. The book does not appear to be particularly common in print3, but if you get the chance to read it, you definitely should.
1Dewar mentions Project Prometheus to explain that it was too early in the program life-cycle to discuss. As it turns out, Project Prometheus went nowhere. In 2017, NASA issued new hardware contracts for exploring the manufacturing and testing requirements for making nuclear propulsion viable, but it is too early to say whether these will yield results, either.
2Bussard is better known for his later work on advanced propulsion, proposing a fusion ramjet fueled by the interstellar medium.
3I believe that it has had only two printings: initially from the University of Kentucky Press in 2004, and a second run from Apogee Books later in the decade. New hardbacks are hundreds of dollars on Amazon. There might be a PDF version floating around, but if there is, I haven’t come across it. Libraries are probably the best bet.