There are generally two ways to establish a truly enabling technology that goes well beyond current capabilities: 1) a nationally mandated program that utilizes a significant fraction of resources over an extended time period or 2) an evolution of the technology via smaller, shorter, more affordable steps. Nearly every technology used today evolved via path #2: automobiles, airplanes, computers, etc. The same is true of all technologies used in space exploration today: solar panels, lightweight structures, power conversion technologies, control systems, propulsion systems, etc. Unfortunately, fission technology has not progressed in a similar matter. In the 1960s, space fission technology was being successfully developed with frequent design, built, and test iterations, which is arguably the best way to develop any technology. With the SNAP and ROVER/NERVA programs, significant progress was being made in all regimes of space nuclear power and propulsion. In the 1970s, an irrational fear of nuclear radiation began to develop that led the creation of cumbersome regulations and bureaucracies; these in turn made nuclear operations increasingly difficult and expensive. In the 1980s, a major space reactor development program (SP-100) was attempted, but the cost and risk of ground testing a prototype became so high that the sponsoring agencies could not maintain support of the project. Not only was the ground test prohibitively expensive, the burdensome nuclear regulations had forced so many design changes in the test article that the “prototype” would have been far from prototypical.
Unfortunately, the environment for nuclear development and testing has gotten continually worse since the 1980’s. Not only has new development been hindered, but the majority of testing facilities and infrastructure has been overtly phased out within the U.S. Currently, there is no chance to sustain a nuclear program that consists of design, build, and test iterations (except for the aforementioned nationally mandated program). The irrational fear of nuclear power is now so extreme that following the devastating Japanese earthquake of 2011, the media coverage of the reactor accident for which radiation caused no measurable harm (present or future) was far greater than the coverage of the thousands of lives lost and the crippling economic loss. These unjustified prejudices are what continually makes doing anything nuclear more and more difficult (and if not for the climate change agenda, nuclear energy might be pushed out altogether – despite being technologically one of the most economical energy sources). In general, politicians and bureaucrats in Washington D.C. recognize the benefits that fission power could have on Earth and in space, but the fear of negative publicity, especially if anything might go wrong, makes them unwilling to champion or fund development of nuclear power systems.
In spite of these headwinds, and an increasingly constrained national budget, a path does exist in which space fission systems could be developed affordably today. The window of opportunity is still open to develop an entry-level fission system that can evolve to the technologies needed to significantly expand into the solar system. The crux of the matter is finding a entry-level system simple enough to be developed affordably, while at the same time providing a capability that is attractive to a near-term mission (unless for some reason the U.S. realizes that developing an entry-level system makes sense purely for the purpose of evolving to future systems, but this kind of foresight is not likely). The key features of an affordable entry-level system are 1) the use of existing nuclear technologies (e.g. fuels and materials) and 2) the development of simple systems that can be qualified without expensive nuclear-powered system tests. Unfortunately, these two features eliminate the vast majority of space fission systems that could be useful, including systems that have been previously attempted in the past. In order for a fission power system to be developed today, the reactor module of this system will need to be so “low-tech” from a nuclear perspective that most nuclear engineers will feel it’s a waste of perfectly good uranium. The good news is that while some nuclear technology has been stuck in the 60s, the rest of the technological world has advanced considerably. Advances in modeling capabilities, power conversion, heat rejection, instrumentation and control, and even resistance heaters will allow us to build an attractive space fission system that utilizes a simple, low-tech reactor.
The second key to an affordable small step is the ability to qualify the system without an expensive nuclear-powered system test or demonstration. Of course the gut reaction of any good engineer is that the best way to prove a nuclear reactor system is to run that nuclear reactor system. True, but as mentioned above, a conventional nuclear-powered test can be prohibitively expensive (and risky). Even then, the system you will test is still not going to be fully prototypic of your flight system, and ground safety concerns will prevent the full exercising of the system. The question then becomes whether you design a system that can be qualified without a ground nuclear-powered test (GNT). A blanket answer cannot be given to this question, but the answer is more likely to be yes for a reactor with low thermal power, simple reactor physics, and simple, loose coupling to the power conversion system; this will be the case for first-step or entry-level space fission system. System dynamics, testing, and how a system could be qualified without a GNT is discussed in the Qualification_Without_GNT reference.
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