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Development and Testing Fission Power Systems Forgotten Reactors Nuclear Electric Propulsion Test Stands

Topaz International part II: The Transition to Collaboration


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Today, we continue our look at the collaboration between the US and the USSR/Russia involving the Enisy reactor: Topaz International. Today, we’ll focus on the transfer from the USSR (which became Russia during this process) to the US, which was far more drama-ridden than I ever realized, as well as the management and bureaucratic challenges and amusements that occurred during the testing. Our next post will look at the testing program that occurred in the US, and the changes to the design once the US got involved. The final post will overview the plans for missions involving the reactors, and the aftermath of the Topaz International Program, as well as the recent history of the Enisy reactor.

For clarification: In this blog post (and the next one), the reactor will mostly be referred to as Topaz-II, however it’s the same as the Enisy (Yenisey is another common spelling) reactor discussed in the last post. Some modifications were made by the Americans over the course of the program, which will be covered in the next post, but the basic reactor architecture is the same.

When we left off, we had looked at the testing history within the USSR. The entry of the US into the list of customers for the Enisy reactor has some conflicting information: according to one document (Topaz-II Design History, Voss, linked in the references), the USSR approached a private (unnamed) US company in 1980, but the company did not purchase the reactor, instead forwarding the offer up the chain in the US, but this account has very few details other than that; according to another paper (US-Russian Cooperation… TIP, Dabrowski 2013, also linked), the exchange built out of frustration within the Department of Defense over the development of the SP-100 reactor for the Strategic Defense Initiative. We’ll look at the second, more fleshed out narrative of the start of the Topaz International Program, as the beginning of the official exchange of technology between the USSR (and soon after, Russia) and the US.

The Topaz International Program (TIP) was the final name for a number of programs that ended up coming under the same umbrella: the Thermionic System Evaluation Test (TSET) program, the Nuclear Electric Propulsion Space Test Program (NEPSTP), and some additional materials testing as part of the Thermionic Fuel Element Verification Program (TFEVP). We’ll look at the beginnings of the overall collaboration in this post, with the details of TSET, NEPSTP, TFEVP, the potential lunar base applications, and the aftermath of the Topaz International Program, in the next post.

Let’s start, though, with the official beginnings of the TIP, and the challenges involved in bringing the test articles, reactors, and test stands to the US in one of the most politically complex times in modern history. One thing to note here: this was most decidedly not the US just buying a set of test beds, reactor prototypes, and flight units (all unfueled), this was a true international technical exchange. Both the American and Soviet (later Russian) organizations involved on all levels were true collaborators in this program, with the Russian head of the program, Academician Nikolay Nikolayvich Ponomarev-Stepnoy, still being highly appreciative of the effort put into the program by his American counterparts as late as this decade, when he was still working to launch the reactor that resulted from the TIP – because it’s still not only an engineering masterpiece, but could perform a very useful role in space exploration even today.

The Beginnings of the Topaz International Program

While the US had invested in the development of thermionic power conversion systems in the 1960s, the funding cuts in the 1970s that affected so many astronuclear programs also bit into the thermionic power conversion programs, leading to their cancellation or diminution to the point of being insignificant. There were several programs run investigating this technology, but we won’t address them in this post, which is already going to run longer than typical even for this blog! An excellent resource for these programs, though, is Thermionics Quo Vadis by the Defense Threat Reduction Agency, available in PDF here: https://www.nap.edu/catalog/10254/thermionics-quo-vadis-an-assessment-of-the-dtras-advanced-thermionics (paywall warning).

Our story begins in detail in 1988. The US was at the time heavily invested in the Strategic Defense Initiative (SDI), which as its main in-space nuclear power supply was focused on the SP-100 reactor system (another reactor that we’ll be covering in a Forgotten Reactors post or two). However, certain key players in the decision making process, including Richard Verga of the Strategic Defense Initiative Organization (SDIO), the organizational lynchpin on the SDI. The SP-100 was growing in both cost and time to develop, leading him to decide to look elsewhere to either meet the specific power needs of SDI, or to find a fission power source that was able to operate as a test-bed for the SDI’s technologies.

Investigations into the technological development of all other nations’ astronuclear capabilities led Dr. Verga to realize that the most advanced designs were those of the USSR, who had just launched the two TOPOL-powered Plasma-A satellites. This led him to invite a team of Soviet space nuclear power program personnel to the Eighth Albuquerque Space Nuclear Power Symposium (the predecessor to today’s Nuclear and Emerging Technologies for Space, or NETS, conference, which just wrapped up recently at the time of this writing) in January of 1991. The invitation was accepted, and they brought a mockup of the TOPAZ. The night after their presentation, Academician Nikolay Nicolayvich Ponomarev-Stepnoy, the Russian head of the Topol program, along with his team of visiting academicians, met with Joe Wetch, the head of Space Power Incorporated (SPI, a company made up mostly of SNAP veterans working to make space fission power plants a reality), and they came to a general understanding: the US should buy this reactor from the USSR – assuming they could get both governments to agree to the sale. The terms of this “sale” would take significant political and bureaucratic wrangling, as we’ll see, and sadly the problems started less than a week later, thanks to their generosity in bringing a mockup of the Topaz reactor with them. While the researchers were warmly welcomed, and they themselves seemed to enjoy their time at the conference, when it came time to leave a significant bureaucratic hurdle was placed in their path.

Soviet researchers at Space Nuclear Power Symposium, 1991, image Dabrowski

This mockup, and the headaches surrounding being able to take it back with the researchers, were a harbinger of things to come. While this mockup was non-functional, but the Nuclear Regulatory Commission claimed that, since it could theoretically be modified to be functional (a claim which I haven’t found any evidence for, but is theoretically possible), and as such was considered a “nuclear utilization facility” which could not be shipped outside the US. Five months later, and with the direct intervention of numerous elected officials, including US Senator Pete Domenici, the mockup was finally returned to Russia. This decision by the NRC led to a different approach to importing further reactors from the USSR and Russia, when the time came to do this. The mockup was returned, however, and whatever damage the incident caused to the newly-minted (hopeful) partnership was largely weathered thanks to the interpersonal relationships that were developed in Albuquerque.

Teams of US researchers (including Susan Voss, who was the major source for the last post) traveled to the USSR, to inspect the facilities used to build the Enisy (Yenisey is another common spelling, the reactor was named after the river in Siberia). These visits started in Moscow, with Drs Wetch and Britt of SPI, when a revelation came to the American astronuclear establishment: there wasn’t one thermionic reactor in the USSR, but two, and the most promising one was available for potential export and sale!

These visits continued, and personal relationships between the team members from both sides of the Iron Curtain grew. Due to headaches and bureaucratic difficulties in getting technical documentation translated effectively in the timeframe that the program required, often it was these interpersonal relationships that allowed the US team to understand the necessary technical details of the reactor and its components. The US team also visited many of the testing and manufacturing locations used in the production and development of the Enisy reactor (if you haven’t read it yet, check out the first blog post on the Enisy for an overview of how closely these were linked), as well as observing testing in Russia of these systems. This is also the time when the term “Topaz-II” was coined by one of the American team members, to differentiate the reactor from the original Topol (known in the west as Topaz, and covered in our first blog post on Soviet astronuclear history) in the minds of the largely uninformed Western academic circles.

The seeds of the first cross-Iron Curtain technical collaboration on astronuclear systems development, planted in Albuquerque, were germinating in Russian soil.

The Business of Intergovernmental Astronuclear Development

During this time, due to the headaches involved in both the US and the USSR from a bureaucratic point of view (I’ve never found any information that showed that the two teams ever felt that there were problems in the technological exchange, rather they all seem to be political and bureaucratic in nature, and exclusively from outside the framework of what would become known as the Topaz International Program), two companies were founded to provide an administrative touchstone for various points in the technological transfer program.

The first was International Scientific Products, which from the beginning (in 1989) was made specifically to facilitate the purchase of the reactors for the US, and worked closely with the SDIO Dr. Verga was still intimately involved, and briefed after every visit to Russia on progress in the technical exchange and eventual purchase of the reactors. This company was the private lubricant for the US government to be able to purchase these reactor systems (for reasons too complex to get into in this blog post). The two main players in ISP were Drs Wetch and Britt, who also appear to be the main administrative driving force in the visits. The company gave a legal means to transmit non-classified data from the USSR to the US, and vice versa. After each visit, these three would meet, and Dr. Verga kept his management at SDIO consistently briefed on the progress of the program.

The second was the International Nuclear Energy Research and Technology corporation, known as INERTEK. This was a joint US-USSR company, involving the staff of ISP, as well as individuals from all of the Soviet team of design bureaus, manufacturing centers (except possibly in Talinn, but I haven’t been able to confirm this, it’s mainly due to the extreme loss of documentation from that facility following the collapse of the USSR), and research institutions that we saw in the last post. These included the Kurchatov Institute of Atomic Energy (headed by Academician and Director Ponomarev-Stepnoy, the head of the Russian portion of the Topaz International Program), the Scientific Industrial Association “LUCH” (represented by Deputy Director Yuri Nikolayev), the Central Design Bureau for Machine Building (represented by Director Vladmir Nikitin), and the Keldysh Institute of Rocket Research (represented by Director Academician Anatoli Koreteev). INERTEK was the vehicle by which the technology, and more importantly to the bureaucrats the hardware, would be exported from the USSR to the US. Academician Ponomarev-Stepnoy was the director of the company, and Dr Wetch was his deputy. Due to the sensitive nature of the company’s focus, the company required approval from the Ministry of Atomic Energy (Minatom) in Moscow, which was finally achieved in December 1990.

In order to gain this approval, the US had to agree to a number of demands from Minatom. This included: the Topaz-II reactors had to be returned to Russia after the testing and that the reactors could not be used for military purposes. Dr. Verga insisted on additional international cooperation, including staff from the UK and France. This not only was a cost-saving measure, but reinforced the international and transparent nature of the program, and made military use more challenging.

While this was occurring, the Americans were insistent that the non-nuclear testing of the reactors had to be duplicated in the US, to ensure they met American safety and design criteria. This was a major sticking point for Minatom, and delayed the approval of the export for months, but the Americans did not slow in their preparations for building a test facility. Due to the concentration of space nuclear power research resources in New Mexico (with Los Alamos and Sandia National Laboratories, the US Air Force Philips Laboratory, and the University of New Mexico’s New Mexico Engineering Research Institute (NMERI), as well as the presence of the powerful Republican senator Pete Domenici to smooth political feathers in Washington, DC (all of the labs were within his Senatorial district in the north of the state), it was decided to test the reactors in Albuquerque, NM. The USAF purchased an empty building from the NMERI, and hired personnel from UNM to handle the human resources side of things. The selection of UNM emphasized the transparent, exploratory nature of the program, an absolute requirement for Minatom, and the university had considerable organizational flexibility when compared to either the USAF or the DOE. According to the contract manager, Tim Stepetic:

The University was very cooperative and accommodating… UNM allowed me to open checking accounts to provide responsive payments for the support requirements of the INTERTEK and LUCH contracts – I don’t think they’ve ever permitted such checkbook arrangements either before or since…”

These freedoms were necessary to work with the Russian team members, who were in culture shock and dealing with very different organizational restrictions than their American counterparts. As has been observed both before and since, the Russian scientists and technicians preferred to save as much of their (generous in their terms) per diem for after the project and the money would go further. They also covered local travel expenses as well. One of the technicians had to leave the US for Russia for his son’s brain tumor operation, and was asked by the surgeon to bring back some Tylenol, a request that was rapidly acquiesced to with bemusement from his American colleagues. In addition, personal calls (of a limited nature due to international calling rates at the time) were allowed for the scientists and technicians to keep in touch with their families and reduce their homesickness.

As should be surprising to no-one, the highly unusual nature of this financial arrangement, as well as the large amount of money involved (which ended up coming out to about $400,000 in 1990s money), a routine audit led to the Government Accounting Office being called in to investigate the arrangement later. Fortunately, no significant irregularities in the financial dealings of the NMERI were found, and the program continued. Additionally, the reuse of over $500,000 in equipment scrounged from SNL and LANL’s junk yards allowed for incredible cost savings in the program.

With the business side of the testing underway, it was time to begin preparations for the testing of the reactors in the US, beginning with the conversion of an empty building into a non-nuclear test facility. The building’s conversion, under the head of Frank Thome on the facilities modification side, and Scott Wold as the TSET training manager, began in April of 1991, only four months after Minatom’s approval of INTERTEK. Over the course of the next year, the facility would be prepared for testing, and would be completed just before the delivery of the first shipment of reactors and equipment from Russia.

By this point, the test program had grown to include two programs. The first was the Thermionic Systems Evaluation Test (TSET), which would study mechanical, thermophysical, and chemical properties of the reactors to verify the data collected in Russia. This was to flight-qualify the reactors for American space mission use, and establish the collaboration of the various international participants in the Topaz International Program.

The second program was the Nuclear Electric Propulsion Space Test Program (NEPSTP); run by the Johns Hopkins Applied Physics Laboratory, and funded by the SDIP Ballistic Missile Defense Organization, it proposed an experimental spacecraft that would use a set of six different electric thrusters, as well as equipment to monitor the environmental effects of both the thrusters and the reactor during operation. Design work for the spacecraft began almost immediately after the TSET program began, and the program was of interest to both the American and Russian parts of the team.

Later, one final program would be added: the Thermionic Fuel Element Verification Program (TFEVP). This program, which had predated TIP, is where many of the UK and French researchers were involved, and focused of increasing the lifetime of the thermionic fuel elements from one year (the best US estimate before the TSET) to at least three, and preferably seven, years. This would be achieved through better knowledge of materials properties, as well as improved manufacturing methods.

Finally, there were smaller programs that were attached to the big three, looking at materials effets in intense radiation and plasma environments, as well as long-term contact with cesium vapor, chemcal reactions within the hardware itself, and the surface electrical properties of various ceramics. These tests, while not the primary focus of the program, WOULD contribute to the understanding of the environment an astronuclear spacecraft would experience, and would significantly affect future spacecraft designs. These tests would occur in the same building as the TSET testing, and the teams involved would frequently collaborate on all projects, leading to a very well-integrated and collegial atmosphere.

Reactor Shipment: A Funny Little Thing Occurred in Russia

While all of this was going on in the Topaz International Program, major changes were happening thoughout the USSR: it was falling apart. From the uprisings in Latvia and Lithuania (violently put down by the Soviet military), to the fall of the Berlin Wall, to the ultimate lowering of the hammer and sickle from the Kremlin in December 1991 and its replacement with the tricolor of the Russian Federation, the fall of the Iron Curtain was accelerating. The TIP teams were continuing to work at their program, knowing that it offered hope for the Topaz-II project as well as a vehicle to form closer technological collaborations with their former adversaries, but the complications would rear their heads in this small group as well.

The American purchase of the Topaz reactors was approved by President George H.W. Bush on 27 March, 1992 during a meeting with his Secretary of State, James Barker, and Secretary of Defense Richard Cheney. This freed the American side of the collaboration to do what needed to be done to make the program happen, as well as begin bringing in Russian specialists to begin test facility preparations.

Trinity site obelisk

The first group of 14 Russian scientists and technicians to arrive in the US for the TSET program arrived on April 3, 1992, but only got to sleep for a few hours before being woken up by their guests (who also brought their families) for a long van journey. This was something that the Russians greatly appreciated, because April 4 is a special day in one small part of the world: it’s one of only two days of the year that the Trinity Site, the location of the first nuclear explosion in history, is open to the public. According to one of them, Georgiy Kompaniets:

It was like for a picnic! And at the entrance to the site there were souvenir vendors selling t-shirts with bombs and rocks supposedly at the epicenter of the blast…” (note: no trinitite is allowed to be collected at the Trinity site anymore, and according to some interpretations of federal law is considered low-level radioactive waste from weapons production)

The Russians were a hit at the Trinity site, being the center of attention from those there, and were interviewed for television. They even got to tour the McDonald ranch house, where the Gadget was assembled and the blast was initiated. This made a huge impression on the visiting Russians, and did wonders in cementing the team’s culture.

Hot air balloon in New Mexico, open source

Another cultural exchange that occurred later (exactly when I’m not sure) was the chance to ride in a hot air balloon. Albuquerque’s International Balloon Fiesta is the largest hot air ballooning event in the world, and whenever atmospheric conditions are right a half dozen or more balloons can be seen floating over the city. A local ballooning club, having heard about the Russian scientists and technicians (they had become minor local celebrities at this point) offered them a free hot air balloon ride. This is something that the Russians universally accepted, since none of them had ever experienced this.

According to Boris Steppenov:

The greatest difficulty, it seemed, was landing. And it was absolutely forbidden to touch down on the reservations belonging to the Native Americans, as this would be seen as an attack on their land and an affront to their ancestors…

[after the flight] there were speeches, there were oaths, there was baptism with champagne, and many other rituals. A memory for an entire life!”

The balloon that Steppenov flew in did indeed land on the Sandia Pueblo Reservation, but before touchdown the tribal police were notified, and they showed up to the landing site, issued a ticket to the ballooning company, and allowed them to pack up and leave.

These events, as well as other uniquely New Mexican experiences, cemented the TIP team into a group of lifelong friends, and would reinforce the willingness of everyone to work together as much as possible to make TIP as much of a success as it could be.

C-141 taking off, image DOD

In late April, 1992, a team of US military personnel (led by Army Major Fred Tarantino of SDIO, with AF Major Dan Mulder in charge of logistics), including a USAF Airlift Control Element Team, landed in St. Petersburg on a C-141 and C-130, carrying the equipment needed to properly secure the test equipment and reactors that would be flown to the US. Overflight permissions were secured, and special packing cases, especially for the very delicate tungsten TISA heaters, were prepared. These preparations were complicated by the lack of effective packing materials for these heaters, until Dr. Britt of both ISP and INTERTEK had the idea of using foam bedding pads from a furniture store. Due to the large size and weight of the equipment, though, the C-141 and C-130 aircraft were not sufficient for airlifting the equipment, so the teams had to wait on the larger C-5 Galaxy transports intended for this task, which were en route from the US at the time.

Sadly, when the time came for the export licenses to be given to the customs officer, he refused to honor them – because they were Soviet documents, and the Soviet Union no longer existed. This led Academician Ponomarev-Stepnoy and INTERTEK’s director, Benjamin Usov, to travel to Moscow on April 27 to meet with the Chairman of the Government, Alexander Shokhin, to get new export licenses. After consulting with the Minister of Foreign Economic Relations, Sergei Glazev, a one-time, urgent export license was issued for the shipment to the US. This was then sent via fast courier to St. Petersburg on May 1.

C-5 Galaxy, image USAF

The C-5s, though, weren’t in Russia yet. Once they did land, though, a complex paperwork ballet needed to be carried out to get the reactors and test equipment to America. First, the reactors were purchased by INTERTEK from the Russian bureaus responsible for the various components. Then, INTERTEK would sell the reactors and equipment to Dr. Britt of ISP once the equipment was loaded onto the C-5. Dr. Britt then immediately resold the equipment to the US government. This then avoided the import issues that would have occurred on the US side if the equipment had been imported by ISP, a private company, or INTERTEK, a Russian-led international consortium.

One of them landed in St. Petersburg on May 6, was loaded with the two Topaz-II reactors (V-71 and Ya-21U) and as much equipment as could be fit in the aircraft, and left the same day. It would arrive in Albuquerque on May 7. The other developed maintenance problems, and was forced to wait in England for five days, finally arriving on May 8. The rest of the equipment was loaded up (including the Baikal vacuum chamber), and the plane left later that day. Sadly, it ran into difficulties again upon reaching England, as was forced to wait two more days for it to be repaired, arriving in Albuquerque on May 12.

Preparations for Testing: Two Worlds Coming Together

Unpacking and beryllium checks at TSET Facility in Albuquerque, Image DOE/NASA

Once the equipment was in the US, detailed examination of the payload was required due to the beryllium used in the reflectors and control drums of the reactor. Berylliosis, or the breathing in of beryllium dust, is a serious health issue, and one that the DOE takes incredibly seriously (they’ll evacuate an entire building at the slightest possibility that beryllium dust could be present, at the cost of millions of dollars on occasion). Detailed checks, both before the equipment was removed from the aircraft and during the unpackaging of the reactors. However, no detectable levels of beryllium dust were detected, and the program continued with minimal disruption.

Then it came time to unbox the equipment, but another problem arose: this required the approval of the director of the Central Design Bureau of Heavy Machine Building, Vladmir Nikitin, who was in Moscow. Rather than just call him for approval, Dr Britt called and got approval for Valery Sinkevych, the Albuquerque representative for INTERTEK, to have discretional control over these sorts of decisions. The approval was given, greatly smoothing the process of both setup and testing during TIP.

Sinkevych, Scott Wold and Glen Schmidt worked closely together in the management of the project. Both were on hand to answer questions, smooth out difficulties, and other challenges in the testing process, to the point that the Russians began calling Schmidt “The Walking Stick.” His response was classic: that’s my style, “Management by Walking Around.”

Soviet technicians at TSET Test Facility, image Dabrowski

Every day, Schmidt would hold a lab-wide meeting, ensuring everyone was present, before walking everyone through the procedures that needed to be completed for the day, as well as ensuring that everyone had the resources that they needed to complete their tasks. He also made sure that he was aware of any upcoming issues, and worked to resolve them (mostly through Wetch and Britt) before they became an issue for the facility preparations. This was a revelation to the Russian team, who despite working on the program (in Russia) for years, often didn’t know anything other than the component that they worked on. This synthesis of knowledge would continue throughout the program, leading to a far

Initial estimates for the time that it would take to prepare the facility and equipment for testing of the reactors were supposed to be 9 months. Due to both the well-integrated team, as well as the more relaxed management structure of the American effort, this was completed in only 6 ½ months. According to Sinkevych:

The trust that was formed between the Russian and American side allowed us in an unusually short time to complete the assembly of the complex and demonstrate its capabilities.”

This was so incredible to Schmidt that he went to Wetch and Britt, asking for a bonus for the Russians due to their exceptional work. This was approved, and paid proportional to technical assignment, duration, and quality of workmanship. This was yet another culture shock for the Russian team, who had never received a bonus before. The response was twofold: greatly appreciative, and also “if we continue to save time, do we get another bonus?” The answer to this was a qualified “perhaps,” and indeed one more, smaller bonus was paid due to later time savings.

Installation of Topaz-II reactor at TSET Facility, image DOE/NASA

Mid-Testing Drama, and the Second Shipment

Both in the US and Russia, there were many questions about whether this program was even possible. The reason for its success, though, is unequivocally that it was a true partnership between the American and Russian parts of TIP. This was the first Russian-US government-to-government cooperative program after the fall of the USSR. Unlike the Nunn-Lugar agreement afterward, TIP was always intended to be a true technological exchange, not an assistance program, which is one of the main reasons why the participants of TIP still look fondly and respectfully at the project, while most Russian (and other former Soviet states) participants in N-L consider it to be demeaning, condescending, and not something to ever be repeated again. More than this, though, the Russian design philosophy that allowed full-system, non-nuclear testing of the Topaz-II permanently changed American astronuclear design philosophy, and left its mark on every subsequent astronuclear design.

However, not all organizations in the US saw it this way. Drs. Thorne and Mulder provided excellent bureaucratic cover for the testing program, preventing the majority of the politics of government work from trickling down to the management of the test itself. However, as Scott Wold, the TSET training manager pointed out, they would still get letters from outside organizations stating:

[after careful consideration] they had concluded that an experiment we proposed to do wouldn’t be possible and that we should just stop all work on the project as it was obviously a waste of time. Our typical response was to provide them with the results of the experiment we had just wrapped up.”

As mentioned, this was not uncommon, but was also a minor annoyance. In fact, if anything it cemented the practicality of collaborations of this nature, and over time reduced the friction the program faced through proof of capabilities. Other headaches would arise, but overall they were relatively minor.

Sadly, one of the programs, NEPSTP, was canceled out from under the team near the completion of the spacecraft. The new Clinton administration was not nearly as open to the use of nuclear power as the Bush administration had been (to put it mildly), and as such the program ended in 1993.

One type of drama that was avoided was the second shipment of four more Topaz-II reactors from Russia to the US. These were the Eh-40, Eh-41, Eh-43, and Eh-44 reactors. The use of these terms directly contradicts the earlier-specified prefixes for Soviet determinations of capabilities (the systems were built, then assessed for suitability for mechanical, thermal, and nuclear capabilities after construction, for more on this see our first Enisy post here). These units were for: Eh-40 thermal-hydraulic mockup, with a functioning NaK heat rejection system, for “cold-test” testing of thermal covers during integration, launch, and orbital injection; Eh-41 structural mockup for mechanical testing, and demonstration of the mechanical integrity of the anticriticality device (more on that in the next post), modified thermal cover, and American launch vehicle integration; Eh-43 and -44 were potential flight systems, which would undergo modal testing, charging of the NaK coolant system, fuel loading and criticality testing, mechanical vibration, shock, and acoustic tests, 1000 hour thermal vacuum steady-state stability and NaK system integrity tests, and others before launch.

An-124, image Wikimedia

How was drama avoided in this case? The previous shipment was done by the US Air Force, which has many regulations involved in the transport of any cargo, much less flight-capable nuclear reactors containing several toxic substances. This led to delays in approval the first time this shipment method was used. The second time, in 1994, INTERTEK and ISP contracted a private cargo company, Russian Volga Dnepr Airlines, to transport these four reactors. In order to do this, Volga Dnepr Airlines used their An-124 to fly these reactors from St. Petersburg to Albuquerque.

For me personally, this was a very special event, because I was there. My dad got me out of school (I wasn’t even a teenager yet), drove me out to the landing strip fence at Kirtland AFB, and we watched with about 40 other people as this incredible aircraft landed. He told me about the shipment, and why they were bringing it in, and the seed of my astronuclear obsession was planted.

No beryllium dust was found in this shipment, and the reactors were prepared for testing. Additional thermophysical testing, as well as design work for modifications needed to get the reactors flight-qualified and able to be integrated with the American launchers, were conducted on these reactors. These tests and changes will be the subject of the next blog post, as well as the missions that were proposed for the reactors.

These tests would continue until 1995, and the end of testing in Albuquerque. All reactors were packed up, and returned to Russia per the agreement between INTERTEK and Minatom. The Enisy would continue to be developed in Russia until at least 2007.

More Coming Soon!

The story of the Topaz International Program is far from over. The testing in the US, as well as the programs that the US/Russian team had planned have not even been touched on yet besides very cursory mentions. These programs, as well as the end of the Topaz International Program and the possible future of the Enisy reactor, are the focus of our next blog post, the final one in this series.

This program provided a foundation, as well as a harbinger of challenges to come, in international astronuclear collaboration. As such, I feel that it is a very valuable subject to spend a significant amount of time on.

I hope to have the next post out in about a week and a half to two weeks, but the amount of research necessary for this series has definitely surprised me. The few documents available that fill in the gaps are, sadly, behind paywalls that I can’t afford to breach at my current funding availability.

As such, I ask, once again, that you support me on Patreon. You can find my page at https://www.patreon.com/beyondnerva every dollar counts.

References:

US-Russian Cooperation in Science and Technology: A Case Study of the TOPAZ Space-Based Nuclear Reactor International Program, Dabrowski 2013 https://www.researchgate.net/profile/Richard_Dabrowski/publication/266516447_US-Russian_Cooperation_in_Science_and_Technology_A_Case_Study_of_the_TOPAZ_Space-Based_Nuclear_Reactor_International_Program/links/5433d1e80cf2bf1f1f2634b8/US-Russian-Cooperation-in-Science-and-Technology-A-Case-Study-of-the-TOPAZ-Space-Based-Nuclear-Reactor-International-Program.pdf

Topaz-II Design Evolution, Voss 1994 http://gnnallc.com/pdfs/NPP%2014%20Voss%20Topaz%20II%20Design%20Evolution%201994.pdf

Categories
Development and Testing Fission Power Systems Forgotten Reactors History Test Stands

Topaz International part 1: ENISY, the Soviet Years

Hello, and welcome back to Beyond NERVA! Today, we’re going to return to our discussion of fission power plants, and look at a program that was unique in the history of astronuclear engineering: a Soviet-designed and -built reactor design that was purchased and mostly flight-qualified by the US for an American lunar base. This was the Enisy, known in the West as Topaz-II, and the Topaz International program.

This will be a series of three posts on the system: this post focuses on the history of the reactor in the Soviet Union, including the testing history – which as we’ll see, heavily influenced the final design of the reactor. The next will look at the Topaz International program, which began as early as 1980, while the Soviet Union still appeared strong. Finally, we’ll look at two American uses for the reactor: as a test-bed reactor system for a nuclear electric test satellite, and as a power supply for a crewed lunar base. This fascinating system, and the programs associated with it, definitely deserve a deep dive – so let’s jump right in!

We’ve looked at the history of Soviet astronuclear engineering, and their extensive mission history. The last two of these reactors were the Topaz (Topol) reactors, on the Plasma-A satellites. These reactors used a very interesting type of power conversion system: an in-core thermionic system. Thermionic power conversion takes advantage of the fact that certain materials, when heated, eject electrons, gaining a positive static charge as whatever the electrons impact gain a negative charge. Because the materials required for a thermionic system can be made incredibly neutronically robust, they can be placed inside the core of the reactor itself! This is a concept that I’ve loved since I first heard of it, and remains as cool today as it did back then.

Diagram of multi-cell thermionic fuel element concept, Bennett 1989

The original Topaz reactor used a multi-cell thermionic element concept, where fuel elements were stacked in individual thermionic conversion elements, and several of these were placed end-to-end to form the length of the core. While this is a perfectly acceptable way to set up one of these systems, there are also inefficiencies and complexities associated with so many individual fuel elements. An alternative would be to make a single, full-length thermionic cell, and use either one or several fuel rods inside the thermionic element. This is the – wait for it – single cell thermionic element design, and is the one that was chosen for the Enisy/Topaz-II reactor (which we’ll call Enisy in this post, since it’s focusing on the Soviet history of the reactor). While started in 1967, and tested thoroughly in the 70s, it wasn’t flight-qualified until the 80s… and then the Soviet Union collapsed, and the program died.

After the fall of the USSR, there was a concerted effort by the US to keep the specialist engineers and scientists of the former Soviet republics employed (to ensure they didn’t find work for international bad actors such as North Korea), and to see what technology had been developed behind the Iron Curtain that could be purchased for use by the US. This is where the RD-180 rocket engine, still in use by the United Launch Alliance Atlas rockets, came from. Another part of this program, though, focused on the extensive experience that the Soviets had in astronuclear missions, and in paricular the most advanced – but as yet unflown – design of the renowned NPO Luch design bureau, attached to the Ministry of Medium Industry: the Enisy reactor (which had the US designation of Topaz-II due to early confusion about the design by American observers).

Enisy power supply, image Department of Defense

The Enisy, in its final iteration, was designed to have a thermal output of 115 kWt (at the beginning of life), with a mission requirement of at least 6 kWe at the electrical outlet terminals for at least three years. Additional requirements included a ten year shelf life after construction (without fissile fuel, coolant, or other volatiles loaded), a maximum mass of 1061 kg, and prevention of criticality before achieving orbit (which was complicated from an American point of view, more on that below). The coolant for the reactor remained NaK-78, a common coolant in most reactors we’ve looked at so far. Cesium was stored in a reservoir at the “bottom” (away from the spacecraft) end of the reactor vessel, to ensure the proper partial pressure between the cathode and anode of the fuel elements, which would leak out over time (about 0.5 g/day during operation). This was meant to be the next upgrade in the Soviet astronuclear fleet, and as such was definitely a step above the Topaz-I reactor.

Perhaps the most interesting part of the design is that it was designed to be able to be tested as a complete system without the use of fissile fuels in the reactor. Instead, electrical resistance heaters could be inserted in the thermionic fuel elements to simulate the fission process, allowing for far more complete testing of the system in flight configuration before launch. This design decision heavily influenced US nuclear power plant design and testing procedures, and continues to influence designs today (the induction heating testing of the KRUSTY thermal simulator is a good recent example of this concept, even if it’s been heavily modified for the different reactor geometry), however, the fact that the reactor used cylindrical fuel elements made this process much easier.

So what did the Enisy look like? This changed over time, but we will look at the basics of the power plant’s design in its final Soviet iteration in this post, and the examine the changes that the Americans made during the collaboration in the next post. We’ll also look at why the design changed as it did.

First, though, we need to look at how the system worked, since compared to every system that we’ve looked at in depth, the physics behind the power conversion system are quite novel.

Thermionics: How to Keep Your Power Conversion System in the Core

We haven’t looked at power conversion systems much in this blog yet, but this is a good place to discuss the first kind as it’s so integral to this reactor. If the details of how the power conversion system actually worked don’t interest you, feel free to skip to the next section, but for many people interested in astronuclear design this power conversion system offers the promise to potentially be the most efficient and reliable option available for in-space nuclear reactors geared towards electricity production.

In short, thermionic reactions are those that occur when a material is heated and gives off charged particles. This is something that has been known since ancient times, even though the physical mechanism was completely unknown until after the discovery of the electron. The name comes from the term “thermions,” or “thermal ions.” One of the first to describe this effect used a hot anode in a vacuum: the modern incandescent lightbulb: Thomas Edison, who observed a static charge building up on the glass of his bulbs while they were turned on. However, today this has expanded to include the use of anodes, as well as solid-state systems and systems that don’t have a vacuum.

The efficiency of these systems depends on the temperature difference between the anode and cathode, the work function (or minimum thermodynamic work needed to remove an electron from a solid to a vacuum immediately outside the solid surface) of the emitter used, and the Boltzmann Constant (which relates to the average kinetic energy of particles in a gas), as well as a number of other factors. In modern systems, however, the structure of a thermionic convertor which isn’t completely solid state is fairly standard: a hot cathode is separated from a cold anode, with cesium vapor in between. For nuclear systems, the anode is often tungsten, the cathode seems to vary depending on the system, and the gap between – called the inter-electrode gap – is system specific.

The cesium exists in an interesting state of matter. Solid, liquid, gas, and plasma are familiar to pretty much everyone at this point, but other states exist under unusual circumstances; perhaps the best known is a supercritical fluid, which exhibits the properties of both a liquid and a gas (although this is a range of possibilities, with some having more liquid properties and some more gaseous). The one that concerns us today is something called Rydberg matter, one of the more exotic forms of matter – although it has been observed in many places across the universe. In its simplest form, Rydberg matter can be seen as small clusters of interconnected molecules within a gas (the largest number of atoms observed in a laboratory is 91, according to Wikipedia, although there’s evidence for far larger numbers in interstellar gas clouds). These clumps end up affecting the electron clouds of those atoms in the clusters, causing them to orbit across the nuclei of those atoms, causing a new lowest-energy state for the entire cluster to occur. These structures don’t degrade any faster under radioactive bombardment due to a number of quantum mechanical properties, which brought them to the attention of the Los Alamos Scientific Laboratory staff in the 1950s, and a short time later Soviet nuclear physicists as well.

This sounds complex, and it is, but the key point is this: because the clumps act as a unit within Rydberg matter, their ability to transmit electricity is enhanced compared to other gasses. In particular, cesium seems to be a very good vehicle for creating Rydberg matter, and cesium vapor seems to be the best available for the gap between the cathode and anode of a thermionic convertor. The density of the cesium vapor is variable and dependent on many factors, including the materials properties of the cathode and anode, the temperature of the cathode, the inter-electrode gap distance, and a number of other factors. Tuning the amount of cesium in the inter-electrode gap is something that must occur in any thermionic power conversion system; in fact the original version of the Enisy had the ability to vary the inter-electrode gap pressure (this was later dropped when it was discovered to be superfluous to the efficient function of the reactor).

This type of system comes in two varieties: in-core and out-of-core. The out-of-core variant is very similar to the power conversion systems we saw (briefly) on the SNAP systems: the coolant from the reactor passes around or through the radiation shield of the system, heats the anode, which then emits electrons into the gap, collected by the cathode, and then the electricity goes through the power conditioning unit and into the electrical system of the spacecraft. Because thermionic conversion is theoretically more efficient, and in practice is more flexible in temperature range, than thermoelectric conversion, even keeping the configuration of the power conversion system’s relationship to the rest of the power plant offers some advantages.

The in-core variant, on the other hand, wraps the power conversion system directly around the fissile fuel in the core, with electrical power being conducted out of the core itself and through the shield. The coolant runs across the outside of the thermionic unit, providing the thermal gradient for the system to work, and then exits the reactor. While this increases the volume of the core (admittedly, not by much), it also eliminates the need for more complex plumbing for the primary coolant loop. Additionally, it allows for less heat loss from the coolant having to travel a farther difference. Finally, there’s far less chance of a stray meteor hitting your power conversion system and causing problems – if a thermionic fuel element is damaged by a foreign object, you’re going to have far bigger problems with the system as a whole, since it means that it damaged your control systems and pressure vessel on the way to damaging your power conversion unit!

The in-core thermionic power conversion system, while originally proposed by the US, was seen as a curiosity on their side of the Iron Curtain. Some designs were proposed, but none were significantly researched to the level of being able to be serious contenders in the struggle to gain the significant funding needed to develop as complex a system as an astronuclear fission power plant, and the low conversion efficiency available in practice prevents its application in terrestrial power plants, which to this day continue to use steam turbine generators.

On the other side of the Iron Curtain, however, this was seen as the ideal solution for a power conversion system: the only systems needed for the system to work could be solid-state, with no moving parts: heaters to vaporize the cesium, and electromagnetic pumps to move it through the reactor. Greater radiation resistance and more flexible operating temperatures, as well as greater conversion efficiency, all offered more promise to Soviet astronuclear systems designers than the thermoelectric path that the US ended up following. The first Soviet reactor designed for in-space use, the Romashka, used a thermionic power conversion system, but the challenges involved in the system itself led the Krasnya Zvezda design bureau (who were responsible for the Romasha, Bouk, and Topol reactors) to initially choose to use thermoelectric convertors in their first flight system: the BES-5 Bouk, which we’ve seen before.

Now that we’ve looked at the physics behind how you can place your power conversion system within the reactor vessel of your power plant (and as far as I’ve been able to determine, if you’re looking to generate electricity beyond what a simple sensor needs, this is the only option without going to something very exotic), let’s look at the reactor itself.

Enisy: The Design of the TOPAZ-II Reactor

The Enisy was a uranium oxide fueled, zirconium hydride moderated, sodium-potassium eutectic cooled reactor, which used a single-element thermionic fuel element design for in-core power conversion. The multi-cell version was used in the Topol reactor, where each fuel pellet was wrapped in its own thermionic convertor. This is sometimes called a “flashlight” configuration, since it looks a bit like the batteries in a large flashlight, but this comes at the cost of complexity, mass, and increased inefficiencies. To offset this, many issues are easier to deal with in this configuration, especially as your fuel reaches higher burnup percentages and your fuel swells. The ultimate goal was single-unit thermionic fuel elements, which were realized in the Enisy reactor. While more challenging in terms of materials requirements, the greater simplicity, lower mass, and greater efficiency of the system offered more promise.

The power plant was required to provide 6 kWe of electrical power at the reactor terminals (before the power conditioning unit) at 27 volts. It had to have an operational life of three years, and a storage life if not immediately used in a mission of at least ten years. It also had to have an operational reliability of >95%, and could not under any circumstances achieve criticality before reaching orbit, nor could the coolant freeze at any time during operation. Finally, it had to do all of this in less than 1061 kg (excluding the automatic control system).

TFE Full Length, image DOD

Thirty-seven fuel elements were used in the core, which was contained in a stainless steel reactor vessel. These contained uranium oxide fuel pellets, with a central fission gas void about 22% of the diameter of the fuel pellets to prevent swelling as fission products built up. The emitters were made out of molybdenum, a fairly common choice for in-core applications. Al2O3 (sapphire) insulators were used to electrically isolate the fuel elements from the rest of the core. Three of these would be used to power the cesium heater and pump directly, while another (unknown) number powered the NaK coolant pump (my suspicion is that it’s about the same number). The rest would output power directly from the element into the power conditioning unit on the far side of the power plant.

Enisy Core Cross-section, image DOD

Nine control drums, made mostly out of beryllium but with a neutron poison along one portion of the outer surface (Boron carbide/silicon carbide) surrounded the core. Three of these drums were safety drums, with two positions: in, with the neutron poison facing the center of the core, and out, where the beryllium acted as a neutron reflector. The rest of the drums could be rotated in or out as needed to maintain reactivity at the appropriate level in the core. These had actuators mounted outside the pressure vessel to control the rotation of the drums, and were connected to an automatic control system to ensure autonomous stable function of the reactor within the mission profile that the reactor would be required to support.

Image DOD

The NaK coolant would flow around the fuel elements, driven by an electromagnetic pump, and then pass through a radiator, in an annular flow path immediately surrounding the TFEs. Two inlet and two outlet pipes were used to connect the core to the radiator. In between the radiator and the core was a radiation shield, made up of stainless steel and lithium hydride (more on this seemingly odd choice when we look at the testing history).

The coolant tubes were embedded in a zirconium hydride moderator, which was contained in stainless steel casings.

Finally, a reservoir of cesium was at the opposite end of the reactor from the radiator. This was necessary for the proper functioning of the thermionic fuel elements, and underwent many changes throughout the design history of the reactor, including a significant expansion as the design life requirements increased.

Once the Topaz International program began, additional – and quite significant – changes were made to the reactor’s design, including a new automated control system and an anti-criticality system that actually removed some of the fuel from the core until the start-up commands were sent, but that’s a discussion for the next post.

TISA Heater Installation During Topaz International, image NASA

I saved the coolest part of this system for last: the TISA, or “Thermal Simulators of Apparatus Cores” (the acronym was from the original Russian), heaters. These units were placed in the active section of the thermionic fuel elements to simulate the heat of fission occurring in the thermionic fuel elements, with the rest of the systems and subsystems being in flight configuration. This led to unprecedented levels of testing capability, but at the same time would lead to a couple of problems later in testing – which would be addressed as needed.

How did this design end up this way? In order to understand that, the development and testing process of the Soviet design team must be looked at.

The History of Enisy’s Design

The Enisy reactor started with the development of the thermionic fuel element by the Sukhumi Institute in the early 1960s, which had two options: the single cell and multiple cell variants. In 1967, these two options were split into two different programs: the Topol (Topaz), which we looked at in the Soviet Astronuclear History post, led by the Krasnaya Zvezda design bureau in Moscow, and Enisy, which was headed by the Central Design Bureau of Machine Building in Leningrad (now St. Petersburg). Aside from the lead bureau, in charge of the overall program and system management, a number of other organizations were involved with the fabrication and testing of the reactor system: the design and modeling team consisted of: the Kurchatov Institute of Atomic Energy was responsible for nuclear design and analytics, the Scientific Industrial Association Lutch was responsible for the thermionic fuel elements, the Sukhumi Institute remained involved in the reactor’s automatic control systems design; fabrication and testing was the responsibility of: the Research Institute of Chemical Machine Building for thermal vacuum testing, the Scientific Institute for Instrument Building’s Turaevo nuclear test facility, Kraznoyarsk Spacecraft Designer for mechanical testing and spacecraft integration, Prometheus Laboratory for materials development (including liquid metal eutectic development for the cooling system and materials testing) and welding, and the Enisy manufacturing facility was located in Talinn, Estonia (a decision that would cause later headaches during the collaboration).

The Enisy originally had three customers (the identities of which I am not aware of, simply that at least one was military), and each had different requirements for the reactor. Originally designed to operate at 6 kWe for one year with a >95% success rate, but customer requirements changed both of these characteristics significantly. As an example, one customer needed a one year system life, with a 6 kWe power output, while another only needed 5 kWe – but needed a three year mission lifetime. This longer lifetime ended up becoming the baseline requirement of the system, although the 6 kWe requirement and >95% mission success rate remained unchanged. This led to numerous changes, especially to the cesium reservoir needed for the thermionic convertors, as well as insulators, sensors, and other key components in the reactor itself. As the cherry on top, the manufacture of the system was moved from Moscow to Talinn, Estonia, resulting in a new set of technicians needing to be trained to the specific requirements of the system, changes in documentation, and at the fall of the Soviet Union loss of significant program documentation which could have assisted the Russia/US collaboration on the system.

The nuclear design side of things changed throughout the design life as well. An increase in the number of thermionic fuel elements (TFEs) occurred in 1974, from 31 to 37 in the reactor core, an increase in the height of the “active” section of the TFE, although whether the overall TFE length (and therefore the core length) changed is information I have not been able to find. Additional space in the TFEs was added to account for greater fuel swelling as fission products built up in the fuel pellets, and the bellows used to ensure proper fitting of the TFEs with reactor components were modified as well. The moderator blocks in the core, made out of zirconium hydride, were modified at least twice, including changing the material that the moderator was kept in. Manufacturing changes in the stainless steel reactor vessel were also required, as were changes to the gamma shielding design for the shadow shield. All in all, the reactor went through significant changes from the first model tested to theend of its design life.

Another area with significantly changing requirements was the systems integration side of things. The reactor was initially meant to be launched in a reactor-up position, but this was changed in 1979 to a reactor-down launch configuration, necessitating changes to several systems in what ended up being a significant effort. Another change in the launch integration requirements was an increase in the acceleration levels required during dynamic testing by a factor of almost two, resulting in failures in testing – and resultant redesigns of many of the structures used in the system. Another thing that changed was the boom that mounted the power plant to the spacecraft – three different designs were used through the lifetime of the system on the Russian side of things, and doubtless another two (at least) were needed for the American spacecraft integration.

Perhaps the most changed design was the coolant loop, due to significant problems during testing and manufacturing of the system.

Design Driven by (Expected) Failure: The USSR Testing Program

Flight qualification for nuclear reactors in the USSR at the time was very different from the way that the US did flight qualification, something that we’ll look at a bit more later in this post. The Soviet method of flight qualification was to heavily test a number of test-beds, using both nuclear and non-nuclear techniques, to validate the design parameters. However, the actual flight articles themselves weren’t subjected to nearly the same level of testing that the American systems would be, instead going through a relatively “basic” (according to US sources) workmanship examination before any theoretical launch.

In the US, extensive systems modeling is a routine part of nuclear design of any sort, as well as astronautical design. Failures are not unexpected, but at the same time the ideal is that the system has been studied and modeled mathematically thoroughly enough that it’s not unreasonable to predict that the system will function correctly the first time… and the second… and so on. This takes not only a large amount of skilled intellectual and manual labor to achieve, but also significant computational capabilities.

In the Soviet Union, however, the preferred method of astronautical – and astronuclear – development was to build what seemed to be a well-designed system and then test it, expecting failure. Once this happened, the causes of the failure were analyzed, the problem corrected, and then the newly upgraded design would be tested again… and again, for as many times as were needed to develop a robust system. Failure was literally built into the development process, and while it could be frustrating to correct the problems that occurred, the design team knew that the way their system could fail had been thoroughly examined, leading to a more reliable end result.

This design philosophy leads to a large number of each system needing to be built. Each reactor that was built underwent a post-manufacturing examination to determine the quality of the fabrication in the system, and from this the appropriate use of the reactor. These systems had four prefixes: SM, V, Ya, and Eh. Each system in this order was able to do everything that the previous reactor would be able to do, in addition to having superior capabilities to the previous type. The SM, or static mockup, articles were never built for anything but mechanical testing, and as such were stripped down, “boilerplate” versions of the system. The V reactors were the next step up, which were used for thermophysical (heat transfer, vibration testing, etc) or mechanical testing, but were not of sufficient quality to undergo nuclear testing. The Ya reactors were suitable for use in nuclear testing as well, and in a pinch would be able to be used in flight. The Eh reactors were the highest quality, and were designated potential flight systems.

In addition to this designation, there were four distinct generations of reactor: the first generation was from V-11 to Ya-22. This core used 31 thermionic fuel elements, with a one year design life. They were intended to be launched upright, and had a lightweight radiation shield. The next generation, V-15 to Ya-26, the operational lifetime was increased to a year and a half.

The third generation, V-71 to Eh-42 had a number of changes. The number of TFEs was increased from 31 to 37, in large part to accommodate another increase in design life, to above 3 years. The emitters on the TFEs were changed to the monocrystaline Mo emitters, and the later ones had Nb added to the Mo (more on this below). The ground testing thermal power level was reduced, to address thermal damage from the heating units in earlier non-nuclear tests. This is also when the launch configuration was changed from upright to inverted, necessitating changes in the freeze-prevention thermal shield, integration boom, and radiator mounting brackets. The last two of this generation, Eh -41 and Eh-42, had the heavier radiation shield installed, while the rest used the earlier, lighter gamma shield.

The final generation, Ya-21u to Eh-44, had the longest core lifetime requirement of three years at 5.5 kWe power output. These included all of the other changes above, as well as many smaller changes to the reactor vessel, mounting brackets, and other mechanical components. Most of these systems ended up becoming either Ya or Eh units due to lessons learned in the previous three generations, and all of the units which would later be purchased by the US as flight units came from this final generation.

A total of 29 articles were built by 1992, when the US became involved in the program. As of 1992, two of the units were not completed, and one was never assembled into its completed configuration.

Sixteen of the 21 units were tested between 1970 and 1989, providing an extensive experimental record of the reactor type. Of these tests, thirteen underwent thermal, mechanical, and integration non-nuclear testing. Nuclear testing occurred six times at the Baikal nuclear facility. As of 1992, there were two built, but untested, flight units available: the E-43 and E-44, with the E-45 still under construction.

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Unit Name

Generation

Series #

Core Life

# of TFEs

TFE Generation

ACS Unit

Launch configuration

Manufacturing location

Test type

Test stand

Testing begin

Testing end

Testing duration

System notes

SM-0

0

Static Model 1

n/a

n/a

n/a

Upright

CDBMB

Static

01/01/76

01/01/76

Original mockup, with three main load bearing systems.

SM-1

0

Static Model 2

n/a

n/a

n/a

Inverted

CDBMB

Static

Krasnoyarsk

01/01/83

01/01/84

Inverted launch configuration static test model.

SM-2

0

Static Model 3

n/a

n/a

n/a

Inverted

CDBMB

Static

Krasnoyarsk

01/01/83

01/01/84

Inverted launch configuration static test model.

V-11

1

Prototype 1

1

1

Upright

CDBMB

Electric heat

Baikal

07/23/71

02/03/72

3200

Development of system test methods and operations. Incomplete set of TFEs

V-12

1

Prototype 2

1

31

1

Upright

CDBMB

Electrical

Baikal

06/21/72

04/18/73

850

Development of technology for prelaunch operations and system testing

V-13

1

Prototype 3

1

31

1

Upright

Talinn

Mechanical

Baikal, Mechanical

08/01/72

05/01/73

?

Transportation, dynamic, shock, cold temperature testing. Reliability at freezing and heating.

Ya(?)-20

1

Specimen 1

1

31

1

Upright

Talinn

Nuclear

Romashka

10/01/72

03/01/74

2500

Zero power testing. Neutron physical characteristics, radiation field characterization. Development of nuclear tests methods.

Ya-21

1

Specimen 2

1

31

1

Upright

Talinn

Nuclear

Baikal, Romashka

?

?

?

Nuclear test methods and test stand trials. Prelaunch operations. Neutron plysical characteristics

Ya-22

1

Specimen 3

1

31

1

Upright

Talinn

n/a

n/a

n/a

n/a

n/a

Unfabricated, was intended to use Ya-21 design documents

Unit Name

Generation

Series #

Core Life

# of TFEs

TFE Generation

ACS Unit

Launch configuration

Manufacturing location

Test type

Test stand

Testing begin

Testing end

Testing duration

System notes

V-15

2

Serial 1

1-1.5

31

2

Upright

Talinn

Cold temp

Baikal, Cold Temp Testing

02/12/80

?

Operation and functioning tests at freezing and heating.

V-16

2

Serial 2

1-1.5

31

2

Upright

Talinn

Mechanical, Electrical

Mechanical

08/01/79

12/01/79

2300

Transportation, vibration, shock. Post-mechanical electirc serviceability testing.

Ya-23

2

Serial 3

1-1.5

31

2

SAU-35

Upright

Talinn

Nuclear

Romashka

03/10/75

06/30/76

5000

Nuclear testing revision and development, including fuel loading, radiation and nuclear safety. Studied unstable nuclear conditions and stainless steel material properties, disassembly and inspection. LiH moderator hydrogen loss in test.

Eh-31

2

Serial 4

1-1.5

31

2

SAU-105

Upright

Talinn

Nuclear

Romashka

02/01/76

09/01/78

4600

Nuclear ground test. ACS startup, steady-state functioning, post-operation disassembly and inspection. TFE lifetime limited to ~2 months due to fuel swelling

Ya-24

2

Serial 5

1-1.5

31

2

SAU-105

Upright

Talinn

Nuclear

Tureavo

12/01/78

04/01/81

14000

Steady state nuclear testing. Significant TFE shortening post-irradiation.

(??)-33

2

Serial 6

1-1.5

31

2

Upright

Talinn

Spacecraft integration

Tureavo

n/a

n/a

n/a

TFE needed redesign, no systems testing. Installed at Turaevo as mockup. Used to establish transport and handling procedures

V(?)-25

2

Serial 7

1-1.5

31

2

Upright

Talinn

Spacecraft integration

Krasnoyarsk

n/a

n/a

?

System incomplete. Used as spacecraft mockup, did not undergo physical testing.

(??)-35

2

Serial 8

1-1.5

31

2

Upright

Talinn

Test stand preparation

Baikal

?

?

?

Second fabrication stage not completed. Used for some experiments with Baikal test stand. Disassembled in Sosnovivord.

V(?)-26

2

Serial 9

1-1.5

31

2

Upright

Talinn, CDBMB

n/a

n/a

n/a

n/a

n/a

Refabricated at CDBMB. TFE burnt and damaged during second fadrication. Notch between TISA and emitter

Unit Name

Generation

Series #

Core Life

# of TFEs

TFE Generation

ACS Unit

Launch configuration

Manufacturing location

Test type

Test stand

Testing begin

Testing end

Testing duration

System notes

V-71

3

Serial 10

1.5

37

3

Upright, Inverted

Talinn

Mechanical, Electrical, Spacecraft integration

Baikal, Krasnoyarsk, Cold Temp Testing

01/01/81

01/01/87

1300

Converted from upright to inverted launch configuration, spacecraft integration heavily modified. First to use 37 TFE core configuration. Transport testing (railroad vibration and shock), cold temperature testing. Electrical testing post-mechanical. Zero power testing at Krasnoyarsk.

Ya-81

3

Serial 11

1.5

37

3

Ground control (no ACS)

Inverted

Talinn

Nuclear

Romashka

09/01/80

01/01/83

12500

Nuclear ground test, steady state operation. Leaks observed in two cooling pipes 120 hrs into test; leaks plugged and test continued. Disassembly and inspection.

Ya-82

3

Serial 12

1.5

37

3

Prototype Sukhumi ACS

Inverted

Talinn

Nuclear

Tureavo

09/01/83

11/01/84

8300

Nuclear ground test, startup using ACS, steady state. Initial leak in EM pump led to large leak later in test. Test ended in loss of coolant accident. Reactor disassembled and inspected post-test to determine leak cause.

Eh(?)-37

3

Serial 13

1.5

37

3

Inverted

Talinn

Static

?

?

?

?

Quality not sufficient for flight (despite Eh “flight” designation). Static and torsion tests conducted.

Eh-38

3

Serial 14

1.5

37

3

Factory #1

Inverted

Talinn

Nuclear

Romashka

02/01/86

05/01/86

4700

Nuclear ground test, pre-launch simulation. ACS startup and operation. Steady state test. Post-operation disassembly and examination.

(??)-39

3

Serial 15

1.5

37

3

Inverted

Talinn

special

special

special

special

special

Fabrication begin in Estonia, with some changed components. After changes, system name changed to Eh-41, and serial number changed to 17. Significant reactor changes.

Eh-40

3

Serial 16

1.5

37

3

Inverted

Talinn

Cold temp, coolant flow

?

01/03/88

12/31/88

?

Cold temperature testing. No electrical testing. Filled with NaK during second stage of fabrication.

Eh-41

3

Serial 17

1.5

37

3

Inverted

Talinn

Mechanical, Leak

Baikal, Mechanical

01/01/88

?

?

Began life as Eh(?)-39, post-retrofit designation. Transportation (railroad) dynamic, and impact testing. Leak testing done post-mechanical testing. First use of increased shield mass.

Eh-42

3

Serial 18

1.5

37

3

Inverted

Talinn

n/a

n/a

Critical component welding failure during fabrication. Unit never used.

Unit Name

Generation

Series #

Core Life

# of TFEs

TFE Generation

ACS Unit

Launch configuration

Manufacturing location

Test type

Test stand

Testing begin

Testing end

Testing duration

System notes

Ya-21u

4

Serial 19

3

37

4

Inverted

Talinn

Electrical

Baikal

12/01/87

12/01/89

?

First Gen 4 reactor using modified TFEs. Electrical testing on TFEs conducted. New end-cap insulation on TFEs tested.

Eh-43

4

Serial 20

3

37

4

Inverted

Talinn

n/a

6/30/88 (? Unclear what testing is indicated)

n/a

n/a

n/a

Flight unit. First fabrication phase in Talinn completed, second incomplete as of 1994

Eh-44

4

Serial 21

3

37

4

Inverted

Talinn

n/a

n/a

n/a

n/a

n/a

Flight unit. First fabrication phase in Talinn completed, second incomplete as of 1994

Eh(?)-45

4

Serial 22

3

37

4

Inverted

Talinn

n/a

n/a

n/a

n/a

n/a

Partially fabricated unit with missing components.

Not many fine details are known about the testing of these systems, but we do have some information about the tests that led to significant design changes. These changes are best broken down by power plant subsystem, because while there’s significant interplay between these various subsystems their functionality can change in minor ways quite easily without affecting the plant as a whole. Those systems are: the thermionic fuel elements, the moderator, the pressure vessel, the shield, the coolant loop (which includes the radiator piping), the radiator coatings, the launch configuration, the cesium unit, and the automatic control system (including the sensors for the system and the drum drive units). While this seems like a lot of systems to cover, many of them have very little information about their design history to pass on, so it’s less daunting than it initially appears.

Thermionic Fuel Elements

It should come as no surprise that the thermionic fuel elements (TFEs) were extensively modified throughout the testing program. One of the big problems was short circuiting across the inter-electrode gap due to fuel swelling, although other problems occurred to cause short circuits as well.

Perhaps the biggest change was the change from 31 to 37 TFEs in the core, one of the major changes to minimize fuel swelling. The active core length (where the pellets were) was increased by up to 40 mm (from 335 mm to 375 mm), the inter-electrode gap was widened by 0.05 mm (from 0.45 to 0.5 mm). In addition, the hole through the center of the fuel element was increased in diameter to allow for greater internal swelling, reducing the mechanical stress on the emitter.

The method of attaching the bellows for thermal expansion were modified (the temperature was dropped 10 K) to prevent crystalization of the palladium braze and increase bellows thermal cycling capability after failures on the Ya-24 system (1977-1981).

Perhaps the biggest change was to the materials used in the TFE. The emitter started off as a polycrystaline molybdenum in the first two generations of reactors, but the grain boundaries between the Mo crystals caused brittleness over time. Because of this, they developed the capability to use monocrystalline Mo, which improved performance in the early third generation of reactors – just not enough. In the final version seen in later 3rd generation and fourth generation systems, the Mo was doped with 3% niobium, which created the best available material for the emitter.

There were many other changes during the development of the thermionic fuel elements, including the addition of coatings on some materials for corrosion resistance, changes in electrical insulation type, and others, but these were the most significant in terms of functionality of the TFEs, and their impact on the overall systems design.

ZrH Moderator

The zirconium hydride neutron moderator was placed around the outside of the core. Failures were observed several times in testing, including the Ya-23 test, which resulted in loss of hydrogen in the core and the permanent shutdown of that reactor. Overpower issues, combined with a loss of coolant, led to moderator failure in Ya-82 as well, but in this case the improved H barriers used in the stainless steel “cans” holding the ZrH prevented a loss of hydrogen accident despite the ZrH breaking up (the failure was due to the ZrH being spread more thinly across the reactor, not the loss of H due to ZrH damage).

This development process was one of the least well documented areas of the Soviet program.

Reactor Vessel

Again, this subsystem’s development seems poorly documented. The biggest change, though, seems to be changing the way the triple coating (of chrome, then nickel, then enamel) was applied to the stainless steel of the reactor vessel. This was due to the failure of the Ya-23 unit, which failed at the join between the tube and the end of the tube on one of the TFEs. The crack self-sealed, but for future units the coatings didn’t go all the way to the weld, and the hot CO2 used as a cover gas was allowed to carbonize the steel to prevent fatigue cracking.

Radiation Shield

The LiH component of the radiation shield (for neutron shielding) seems to not have changed much throughout the development of the reactor. The LiH was contained in a 1.5 mm thick stainless steel casing, polished on the ends for reflectivity and coated black on the outside face.

However, the design of the stainless steel casing was changed in the early 1980s to meet more stringent payload gamma radiation doses. Rather than add a new material such as tungsten or depleted uranium as is typical, the designers decided to just thicken the reactor and spacecraft sides of the LiH can to 65 mm and 60 mm respectively. While this was definitely less mass-efficient than using W or U, the manufacturing change was fairly trivial to do with stainless steel, and this was considered the most effective way to ensure the required flux rates with the minimum of engineering challenges.

The first unit to use this was the E-41, fabricated in 1985, which was also the first unit to be tested in the inverted flight configuration. The heavier shield, combined with the new position, led to the failure of one of the shield-to-reactor brackets, as well as the attachment clips for the radiator piping. These components were changed, and no further challenges occurred with the shield in the rest of the test program.

Coolant Loop

The NaK coolant loop was the biggest source of headaches dueing the development of the Enisy. A brief list of failures, and actions taken to correct them, is here:

V-11 (July 1971-February 1972): A weld failed at the join between the radiator tubing and collector during thermophysical testing. The double weld was changed to a triple weld to correct the failure mode.

Ya-21 (1971): This reactor seemed to have everything go wrong with it. Another leak at the same tube-to-collector interface led to the welding on of a small sleeve to repair the crack. This fix seemed to solve the problem of failures in that location.

Ya-23 (March 1975-June 1976): Coolant leak between coolant tube and moderator cavity. Both coating changes and power ramp-up limits eliminated issues.

V-71 (January 1981-1994?): NaK leak in radiator tube after 290 hours of testing. Plugged, testing continued. New leak occurred 210 test hours later, radiator examined under x-ray. Two additional poorly-manufactured tubes replaced with structural supports. One of test reactors sent to US under Topaz International.

Ya-81 (September 1980-January 1983): Two radiator pipe leaks 180 hours into nuclear testing (no pre-nuclear thermophysical testing of unit). Piping determined to be of lower quality after switching manufacturers. Post-repair, the unit ran for 12,500 hours in nuclear power operation.

Ya-82 (September 1983 to November 1984): Slow leak led to coolant pump voiding and oscillations, then one of six pump inlet lines being split. There were two additional contributions to this failure: the square surfaces were pressed into shape from square pipes, which can cause stress microfractures at the corners, and second the inlet pump was forced into place, causing stress fracturing at the joint. This failure led to reactor overheating due to a loss-of-coolant condition, and led to the failure of the ZrH moderator blocks. This led to increased manufacturing controls on the pump assembly, and no further major pump failures were noted in the remainder of the testing.

Eh-38 (February 1986-August 1986): This failure is a source of some debate among the Russian specialists. Some believe it was a slow leak that began shortly after startup, while others believe that it was a larger leak that started at some point toward the end of the 4700 hour nuclear test. The exact location of the leak was never located, however it’s known that it was in the upper collector of the radiator assembly.

Ya-21u (December 1987-December 1989): Caustic stress-corrosion cracking occurred about a month and a half into thermophysical testing in the lower collector assembly, likely caused by a coating flaw growing during thermal cycling. This means that subsurface residual stresses existed within the collector itself. Due to the higher-than-typical (by U.S. standards) carbon content in the stainless steel (the specification allowed for 0.08%-0.12% carbon, rather than the less than 0.8% carbon content in the U.S. SS-321), the steel was less ductile than was ideal, which could have been a source of the flaw growing as it did. Additionally, increased oxygen levels in the NaK coolant could have exacerbated the problem more as well. A combination of ensuring that heat treatments had occurred post-forming, as well as ensuring a more oxygen-poor environment, were essential to reducing the chances of this failure happening again.

Radiator

Pen and ink diagram of radiator, image DOD

The only known data poing on the radiator development was during the Ya-23 test, where the radiator coating changed the nuclear properties of the system at elevated temperature (how is unknown). This was changed to something that would be less affected by the radiation environment. The final radiator configuration was a chrome and polymer substrate with an emissivity of 0.85 at beginning of life.

Launch configuration

As we saw, the orientation that the reactor was to be launched in was changed from upright to inverted, with the boom to connect the reactor to the spacecraft being side by side inside the payload fairing. This required the thermal cover used to prevent the NaK from freezing to be redesigned, and modified after the V-13 test, when it was discovered to not be able to prevent freezing of the coolant. The new cover was verified on the V-15 tests, and remained largely unchanged after this.

Some of the load-bearing brackets needed to be changed or reinforced as well, and the clips used to secure the radiator pipes to the structural components of the radiator.

Cesium Supply Unit

For the TFEs to work properly, it was critical that the Cs vapor pressure was within the right pressure range relative tot he temperature of the reactor core. This system was designed from first physical principles, leading to a novel structure that used temperature and pressure gradients to operate. While initially throttleable, but there were issues with this functionality during the Ya-24 nuclear test. This changed when it was discovered that there was an ideal pressure setting for all power levels, so the feed pressure was fixed. Sadly, on the Ya-81 test the throttle was set too high, leading to the need to cool the Cs as it returned to the reservoir.

Additional issues were found in the startup subsystem (a single-use puncture valve) used to vent the inert He gas from the interelectrode gap (this was used during launch and before startup to prevent Cs from liquefying or freezing in the system), as well as to balance the Cs pressure by venting it into space at a rate of about 0.4 g/day. The Ya-23 test saw a sensor not register the release of the He, leading to an upgraded spring for the valve.

Finally, the mission lifetime extension during the 1985/86 timeframe tripled the required lifetime of the system, necessitating a much larger Cs reservoir to account for Cs venting. This went from having 0.455 g to 1 kg. These were tested on Ya-21u and Eh-44, despite one (military) customer objecting due to insufficient testing of the upgraded system. This system would later be tested and found to be acceptable as part of the Topaz International program.

Automatic Control System

The automatic control system, or ACS, was used for automatic startup and autonomous reactor power management, and went through more significant changes than any other system, save perhaps the thermionic fuel elements. The first ACS, called the SAU-35, was used for the Ya-23 ground test, followed by the SAU-105 for the Eh-31 and Ya-24 tests. Problems arose, however, because these systems were manufactured by the Institute for Instrument Building of the Ministry of Aviation Construction, while the Enisy program was under the purview of the Ministry of Atomic Energy, and bureaucratic problems reared their heads.

This led the Enisy program to look to the Sukhumi Institute (who, if you remember, were the institute that started both the Topol and Enisy programs in the 1960s before control was transferred elsewhere) for the next generation of ACS. During this transition, the Ya-81 ground nuclear test occurred, but due to the bureaucratic wrangling, manufacturer change, and ACS certification tests there was no unit available for the test. This led the Ya-81 reactor to be controlled from the ground station. The Ya-82 test was the first to use a prototype Sukhumi-built ACS, with nine startups being successfully performed by this unit.

The loss-of-cooling accident potentially led to the final major change to the ACS for the Eh-38 test: the establishment of an upper temperature limit. After this, the dead-band was increased to allow greater power drift in the reactor (reducing the necessary control drum movement), as well as some minor modifications rerouting the wires to ensure proper thermocouple sensor readings, were the final significant modifications before Topaz International started.

Sensors

The sensors on the Enisy seem to have been regularly problematic, but rather than replace them, they were either removed or left as instrumentation sensors rather than control sensors. These included the volume accumulator sensors on the stainless steel bellows for the thermionic fuel elements (which were removed), and the set of sensors used to monitor the He gas in the TFE gas gap (for fission product buildup), the volume accumulator (which also contained Ar), and the radiation shield. This second set of sensors was kept in place, but was only able to measure absolute changes, not precise measurements, so was not useful for the ACS.

Control Drive Unit

The control drive unit was responsible for the positioning of the control drums, both on startup as well as throughout the life of the reactor to maintain appropriate reactivity and power levels. Like in the SNAP program, these drive systems were a source of engineering headaches.

Perhaps the most recurring problem during the mid-1970s was the failure of the position sensor for the drive system, which was used to monitor the rotational position of the drum relative to the core. This failed in the Ya-20, Ya-21, and Ya-23, after which it was replaced with a sensor of a new design and the problem isn’t reported again. The Ya-81 test saw the loss of the Ar gas used as the initial lubricant in the drive system, and later seizing of the bearing the drive system connected to, leading to its replacement with a graphite-based lubricant.

The news wasn’t all bad, however. The Eh-40 test demonstrated greater control of drum position by reducing the backlash in the kinematic circuit, for instance, and improvements to the materials and coatings used eliminated problems of coating delamination, improving the system’s resistance to thermal cycling and vibrational stresses, and radiator coating issues.

The Eh-44 drive unit was replaced against the advice of one of the Russian customers due to a lack of mandatory testing on the advanced drive system. This system remained installed at the time of Topaz International, and is something that we’ll look at in the next blog post.

A New Customer Enters the Fold

During this testing, an American company (which is not named) was approached about possibly purchasing nearly complete Enisy reactors: the only thing that the Soviets wouldn’t sell was the fissile fuel itself, and that they would help with the manufacturing on. This was in addition to the three Russian customers (at least one of which was military, but again all remain unnamed). This company did not purchase any units, but did go to the US government with this offer.

This led to the Topaz International program, funded by the US Department of Defense’s Ballistic Missile Defense Organization. The majority of the personnel involved were employees of Los Alamos and Sandia National Laboratories, and the testing occurred at Kirtland Air Force Base in Albuquerque, NM.

As a personal note, I was just outside the perimeter fence when the aircraft carrying the test stand and reactors landed, and it remains one of the formational events in my childhood, even though I had only the vaguest understanding of what was actually happening, or that some day, more than 20 years, later, I would be writing about this very program, which I saw reach a major inflection point.

The Topaz International program will be the subject of our next blog post. It’s likely to be a longer one (as this was), so it may take me a little longer than a week to get out, but the ability to compare and contrast Soviet and American testing standards on the same system is too golden an opportunity to pass up.

Stay tuned! More is coming soon!

References:

Topaz II Design Evolution, Voss 1994 https://www.researchgate.net/publication/234517721_TOPAZ_II_Design_Evolution

Russian Topaz II Test Program, Voss 1993 http://gnnallc.com/pdfs_r/SD%2006%20LA-UR-93-3398.pdf

Overview of the Nuclear Electric Propulsion Space Test Program, Voss 1994 https://www.osti.gov/servlets/purl/10157573

Thermionic System Evaluation Test: Ya-21U System, Topaz International Program, Schmidt et al 1996 http://www.dtic.mil/dtic/tr/fulltext/u2/b222940.pdf

Categories
Electric propulsion Fission Power Systems History Nuclear Electric Propulsion

Nuclear Electric Propulsion History Part 1: The Soviet Astronuclear Program

Hello, and welcome back to Beyond NERVA, where we’re getting back into issues directly related to nuclear power in space, rather than how that power is used (as we’ve examined in our last three blog posts on electric propulsion)! However, the new Electric Propulsion page is up on the website, including a summary of all the information that we’ve covered in the last three blog posts, which you can find here [Insert Link]! Also, each type of thruster has its own page as well for easier reference, which are all linked on that summary page! Make sure to check it out!

In this blog series, we’re going to look at nuclear electric power system reactor cores themselves. While we’ve looked at a number of designs for nuclear thermal reactor cores (insert link for NTR-S page), there are a number of differences in those reactor cores compared to ones that are designed purely for electricity production. Perhaps the biggest one is operating temperature, and therefor core lifetime, but because the coolant doesn’t have to be hydrogen, and because the amount of heat produced doesn’t have to be increased as much as possible (there will be a LOT more discussion on this concept in the next series on power conversion systems), the reactor can be run at cooler temperatures, preventing a large amount of thermally related headaches, which makes far more more materials available for the reactor core, and generally simplifying matters.

Nuclear electric power systems are also unique in that they’re the only type of fission powered electrical supply system that’s ever flown. We’ve mentioned those systems briefly before, but we’ll look at some of them more in depth today, and in the next post as well. While there have been many reactor designs proposed over the years, we’re going to focus on the programs developed by the USSR during the Cold War, since they have the longest operational history of any sort of fission-powered heat source in space.

The United States were the first to fly a nuclear reactor in space, the SNAPSHOT mission in 1963; but, sadly, another American reactor was never placed on a spacecraft. The Soviet program was far longer running, flying reactors almost continuously from 1970-1988, often two spacecraft at once. With the fall of the Berlin Wall, and the end of the Cold War, the Soviet astronuclear program ended, and Russia hasn’t flown another nuclear reactor since then. There was a time, though, in the 1990s, that a mission was on the books (but never funded to a sufficient level to have ever flown) to use US-purchased, Russian-built nuclear reactors for an American crewed moon base!

 

History of Soviet In-Space Fission Power Systems

From the beginning, the Soviet in-space nuclear power designers focused on two different design concepts for their power systems: single-cell thermal fuel elements and multi-cell thermal fuel elements. The biggest difference between the two is how many fuel elements are in each thermal fuel element system: the single cell design uses a single fuel element, while the multi-cell option uses multiple fuel elements, separated by passive spacers, moderation blocks, or thermionic power conversion systems. Both designs were extensively researched, and eventually flown, but the initial research focused on the multi-cell approach with the Romashka, (sometimes translated as “Chamomile,” other times as “Daisy”) reactor. This design type led to the BES-5 (Bouk, or “Beech,” flight reactor), whereas the single cell variation led to the TEU-5 TOPOL (TOPAZ-1), which flew twice, and ENISY (TOPAZ-2) reactor, and was later purchased by the US. We won’t be looking in-depth at the ENISY reactor in this post, despite its close relation to the TOPOL, because later in the blog series we’ll be focusing on it far more, the time the Americans bought two of them (and took out an option on another four) and how it could have powered an American lunar base in the 1990s, had the funding been available.

As is our wont here, let’s begin at the beginning, with one of Korolev’s pet projects and the first in-space reactor design of the USSR: Romashka.

 

Romashka: The Reactor that Started it All

 

Romashka 2
Romashka mockup

The Romashka (daisy or chamomile in English) was a Soviet adaptation of an American idea first developed in the US at Los Alamos Labs in the mid 1950s: in-core thermionic energy conversion. We’ll be looking at thermionics much more in-depth in the next post on power conversion systems, but the short version is that it combines a heat pipe (which we looked at in the Kilopower posts) with the tendency for an incandescent light to develop a static charge on its’ bulb. More on the conversion system itself in the next post; but, for now, it’s worth noting that this is a way to actually stick your power conversion system in the core of your reactor; and, as far as I’ve seen, it’s the only one.

Design on this reactor started in 1957, following a trip by Soviet scientists to Los Alamos (where thermionic energy conversion had been proposed, but not yet tested). The design offered the potential to have no moving parts, no pumps, and only needed conductive cooling from the reactor body for thermal management; all very attractive properties for a reactor that would not be able to be maintained for its lifetime. Work was begun at the Institute of Atomic Energy, I.V. Kurchatov in Moscow, but by the end of the program there were many design bureaus involved in the conceptual design, manufacturing, and testing of this reactor.

A series of disc-shaped uranium carbide (UC2) fuel elements were used in this reactor (90% 235U), with holes drilled through the center, and roughly halfway from the central hole of the disc to the edge of the fuel element. Both of these holes were used to thread the thermionic power conversion system through the core of the reactor. Spacing of the fuel elements was provided by a mixture of beryllium oxide and graphite, which was also used to slightly moderate the neutron spectrum – but the neutron spectrum in the reactor remained in the fast spectrum. Surrounding the reactor core itself, both radially and at the ends of the core, were beryllium reflectors. Boron and boron nitride control rods placed in the radial reflector and base axial reflector were used to maintain reactor control through the use of a hydraulic system, however a large negative thermal reactivity coefficient in the reactor core was also meant to largely control the reactor in the case of normal operations. Finally, the reactor was surrounded by a finned steel casing that provided all heat rejection through passive radiation – no pumps required! The nominal operating temperature of the reactor was meant to be between 1200 C and 1800 C at the center of the core, and about 800 C at the edges of the core at the ends of the cylinder.

Romashka 3
Core undergoing assembly, 1966

Construction and warm-critical tests were completed by April, 1966, and testing began in Moscow. There are some indications that materials incompatibilities in the first Romashka built led to the need to rebuild it with different materials, but it’s unclear what would have been changed (the only other reference, besides on a CIA document, to this is that the thermionic fuel element materials were changed in the reactor, so that may be what occurred – more on that in the direct power conversion post). This reactor underwent about 15,000 hours of testing, and in that time period it produced about 6,100 kWh of electricity at a relatively constant rate of 40 kW of thermal and 500-800 W of electrical power (1.5%-2% energy conversion efficiency). Initial testing (about 1200 hours) only rejected heat into a vacuum chamber using the fins’ radiative cooling capability; and testing of other reactor behavior particulars was carried out, including core self-regulation capability. Later tests (about 14,000 hours) were done using natural convection in a helium environment. During these tests, thermal deformation of the core and the reflector led to a reduction in reactivity, which was compensated for with the control system. By the end of the test cycle, electrical power production had dropped by 25%, and overall reactivity had dropped by 30%. Maximum sustained power production was about 450 W, and 88 amps, if all thermionic converters were activated, and pulsed power of up to 800 W was observed at the beginning of the actively controlled tests.

ustanovka-romashka_1
Reactor being installed in test containment vessel, 1966

Korolev planned to pair this reactor with a plasma pulsed power thruster (based on the time period, possibly a pulsed inductive thruster, or PIT, which we looked at briefly in the second blog post on electric propulsion systems). However, two things conspired to end the Romashka system: Korolev’s death in 1966 meant the loss of its’ most powerful proponent; and the development of the more powerful, more efficient Bouk reactor became advanced enough to make that design available for space travel in the same time frame.

While there were plans to adapt Romashka into a small power plant for remote outposts (the core was known as “Gamma”), the testing program ended in 1966, to be supplanted by the BES-5 “Beech”. The legacy of the Romashka reactor lives on, however, as the first successful design of a thermionic energy conversion system for in-core use, a test-bed for the development and testing of thermionic energy conversion materials (more on that in the first power conversion system post); and it remains the father and grandfather of all Russian in-space reactors to ever fly.

 

Bouk: The Most Flown Nuclear Reactor in History

Buk Cutaway
BES-5 Bouk cutaway diagram, image Rosatom

The Bouk (“Beech”) reactor, also known as the “Buk,” or BES-5 reactor, is arguably the most successful astronuclear design in history. Begun in 1960 by the Krasnya Zvesda Scientific and Propulsion Association, this reactor promised greater power output than the Romashka, at the cost of additional complexity, and requiring coolant to operate. From 1963 to 1969, testing of the fuel elements and reactor core was carried out without using the thermoelectric fuel elements (TFE), which were still under development. From 1968 to 1970, three reactor cores with full TFEs were tested at Baikal; and, with successful testing completed, the reactor design was prepared for launch, integrated into the Upravlenniye Sputnik Aktivny (US-A; in the West, RORSAT, for Radar Ocean Reconnaisance SATellite) spacecraft, designed to use radar for naval surveillance.

DOE Sketch based on KOSMOS 954
LLNL sketch of BES-5 based on KOSMOS-954 wreckage, DOE image via Sven Grahn

Rather than having stacked discs of UC2, the BES-5 used 79 fuel rods made out of uranium (90% enriched, total U mass 30 kg) molybdenum alloy metal, encased in high-temperature steel. NaK was used as a coolant for the reactor, pumped using the energy from 19 of the fuel assemblies to run an electromagnetic fuel pump. Producing over 100 kW of thermal energy, after electric conversion using in-core germanium-silicon thermoelectric power conversion elements (which use the difference in charge potential between two different metals along a boundary to create an electrical charge when a temperature gradient is applied across the join; again, more in a later post), a maximum of 5 kW of electrical energy was available for the spacecraft’s instrumentation. The fact that this core used thermoelectric conversion rather than thermionic is a good indicator that the common use of the term, TOPAZ, for this reactor is incorrect. Reactor control was provided by six beryllium reflector drums that would be slowly lowered through holes in the radial reflector over the reactor’s life to increase the local neutron flux to account for the buildup of neutron poisons.

BES-5 Ascent Stage
BES-5 ascent stage cutaway, with core on left and chemical propulsion system on right, Rosatom

One unique aspect to the BES-5 is that the reactor was able to decommission itself at end of life (although this wasn’t always successful) by moving the reactor to a higher orbit and then ejecting the end reflector and fuel assemblies (which were subcritical at time of assembly, and required the Be control rods to be inserted to reach delayed criticality), as well as dumping the NaK coolant overboard. This ensured that the reactor core would not re-enter the atmosphere (although there were two notable exceptions to this, and one late unexpected success). As an additional safety measure following the failure of KOSMOS-954 (more on that below), the reactor was redesigned so that the fuel elements would burn up upon re-entry, diluting the radioactive material to the point that no significant increase in radiation would occur. Over the reactor’s long operational history (31 BES-5 reactors were launched), the lifetime of the reactors was constantly extended, beginning with a lifetime of just 110 minutes (used for radar broadcast testing) to up to 135 days of operational life.

RORSAT_by_Ronald_C._Wittmann,_1982
US-A satellite (with the radiator and ascent stage, but oddly no core), painting by Ronald Wittman 1982

The first BES-5 to be launched was serial number 37 on the KOSMOS-367 satellite on October 3, 1970 (there’s some confusion on this score, with another source claiming it was KOSMOS-469, launched on 25 December 1971). After a very short (110 minute) operational life, the spacecraft was moved into a graveyard orbit and the reactor ejected due to overheating in the reactor core. Three more spacecraft (KOSMOS-402, -469, and 516) were launched over the next two years, with the -469 spacecraft possibly being the first to have the 8.2 GHz side looking radar system that the power plant was selected for. Over time, the US-A spacecraft were launched in parallel, co-planar orbits, usually deployed in pairs with closely attending Russian US-P electronics intelligence satellites (for more on the operational use of the US-A, check out Sven Grahn’s excellent blog on the operational history of the US-A).

Morning Light logo
CNSC/DOE Operation Morning Light logo

The US-A program wasn’t without its failures, sadly, and one led to one of the biggest radiological cleanup missions in the history of nuclear power. On September 18, 1977, a Tsyklon-2 rocket launched from Baikonur Cosmodrome in Khazakhstan carrying the KOSMOS-954 US-A spacecraft on an orbital inclination of 65 degrees. By December, the spacecraft’s orbital maneuvering had become erratic, and Soviet officials contacted US officials that they had lost control of the satellite before they were able to move the reactor core into its’ designated graveyard orbit. On January 24, 1968, the satellite re-entered over Canada, spreading debris over a 600 km long section of the country. Operation Morning Light, the resulting CNES and US DOE program, was able to clear all the debris over several months, in a program that involved hundreds of people from the CNES, DOE, the NEST teams that were then available, and US Military Airlift Command. No fatalities or radiation poisoning cases were reported as a result of KOSMOS-954’s unplanned re-entry, although the remote nature of the re-entry was probably as much of a help as a challenge in this regard. A second KOSMOS spacecraft, KOSMOS-1402, also had its fuel elements re-enter the atmosphere following a failure of the spacecraft to ascend into its graveyard orbit, this time over the North Atlantic. The core re-entered the atmosphere on 23 January 1983, breaking up over the North Atlantic, north of England. No fragments of this reactor were ever recovered, and no significant increase in radioactivity as a result of this unplanned re-entry were detected.

These two incidents caused significant delays in the US-A program, and subsequent redesigns in the reactor as well. However, launches of this system continued until March 14, 1988, with the KOSMOS-1932 mission, which was moved into a graveyard orbit on 20 May, 1988, after a mission time of 66 days. The fate of its’ immediate predecessor, KOSMOS-1900, showed that the additional safety mechanisms for the US-A spacecraft’s reactor were successful: despite an apparent loss of control of the spacecraft, an increasingly eccentric orbit, and the buildup of aerodynamic forces, the reactor core was able to be boosted to a stable graveyard orbit, with the maneuver being completed on 17 October 1988. The main body of the spacecraft re-entered over the Indian Ocean 16 days earlier.

One interesting note on the controversy surrounding these reactor cores’ re-entry into Earth’s atmosphere is that the US planned on doing the exact same thing with the SNAP-10A reactors. The design was supposed to orbit for long enough (on the order of hundreds of year) for the short-lived fission products to decay away, and then the entire reactor would self-disassemble through a combination of mechanical, explosive, and aerodynamic systems; and, as a result, burn up in the upper atmosphere. While the amount of radioactivity that would be added to the atmosphere would be negligible, these accidents showed that this disposal method would not be acceptable; further complicating the American astronuclear program, as well as the one in the USSR. The SNAPSHOT reactor is still in orbit, and is expected to remain there for 2800 years, but considering the fallout of these accidents, retrieval or boosting to a graveyard orbit may be a future mission necessity for this reactor.

The US-A spacecraft demonstrated in-space nuclear fission power, and serial fission power plant production, for over two decades. Despite two major failures resulting in re-entry of the reactor core, the US-A program managed successful operation of the BES-5 reactor for 29 missions, and minimal impact from the two failures. The rest of the BES-5 cores remain parked in graveyard orbits, where they will remain for many hundreds of years until the radioactivity has dropped to natural background radiation.

There is one long-lasting legacy of the BES-5 program on in-orbit space travel, however: the ejected NaK coolant. The coolant remains a cratering hazard for spacecraft in certain orbits, but is not thought to be an object multiplication hazard. It is doubtful that the same core ejection system would be used in a newly designed astronuclear reactor, but this legacy lives on as another example of humanity’s ignorance at the time of a Kessler Syndrome situation.

While this program was not 100% successful, whether from a mission success point of view or from the point of view of it having no ongoing impact from the operations that were carried out, over 25 years of operation of a series of BES-5 reactors remains to this day the most extensive and successful of any astronuclear fission powered design, and it meets or exceeds even the service histories of any RTG design that has been deployed by any country.

 

TOPOL: The Most Powerful Reactor Ever Flown

TOPOL Cutaway
TEU-5 cutaway diagram

The TEU-5 TOPOL (TOPAZ-1) program is the second type of Soviet reactor to fly; and, although it only flew twice, it can be argued to have been even more successful than the BES-5 reactor design. The TEU-5 was the return of the in-core thermionic power conversion system that was first utilized in Romashka; and, just as the Bouk was a step above the Romashka, the Topol was a step beyond that. Thermionic conversion remained more attractive than thermoelectric in terms of wider range of operating capabilities, increased temperature potential, and more forgiving materials requirements, but thermoelectric conversion was able to be readied for flight first. Because of this, and because of the inertia that any flight-tested and more-refined (from a programmatic and serial production sense) program has over one that has yet to fly, the BES-5 flew for over a decade before the TEU-5 would take to orbit.

Despite the different structure, and much higher power, of the TEU-5, the design was able to fulfill the same role of ocean radar reconnaissance; but, initially, it was meant to be a powerful on-orbit TV transmission station. The major advantage of the TEU-5 over the BES-5 is that, due to its higher power level, it wasn’t forced to be in a very low orbit, which increased atmospheric drag, caused the dry mass of the craft to be severely reduced in order to allow for more propellant to be on board, and created a lot of complexity in terms of reactor decommissioning and disposal. Following the KOSMOS-954 and -1402 accidents, the low-flying profile of the US-A satellite was no longer available for astronuclear reactors, and so the orbital altitude increased. TEU-5 offered the capability to get useful image resolution at this higher altitude due to its higher power, and improvements to the (never flown, but ground tested) radar systems.

TOPAZ Core configuration, Bennett
Disgram of multi-cell TFE concept, Bennett 1989

The TOPOL program was begun in the 1960s, under the Russian acronym for Thermionic Experimental Converter in the Active Zone, which translates directly into Topaz in English, but ground testing didn’t begin until 1970. This was a multi-cell thermionic fuel element design similar in basic concept to Romashka, however it was a far more complex design. Instead of a single stack of disc-shaped fuel elements, a “garland” of fuel elements were formed into a thermionic fuel element. The fissile fuel element was surrounded by a thimble of tungsten or molybdenum, which formed the cathode of the thermionic converter, while the anode of the converter was a thin niobium tube; as with most thermionic converters the gap between cathode and anode was filled with cesium vapor. The anode was cooled with pumped NaK, although some sources indicate that lithium was also considered as a coolant for higher-powered versions of the reactor.

BES-5 core cross section
TEU-5 core cross-section, DOE

The differences between the BES-5 and TEU-5 were far more than the power conversion system. Instead of being a fast reactor, the Topaz was designed for the thermal neutron spectrum, and as such used zirconium hydride for in-core moderation (also creating a thermal limitation for the materials in the core; however, hydrogen loss mitigation measures were taken throughout the development process). Rather than using the metal fuels that its predecessor had, or the carbides of the Romashka, the Topol used a far more familiar material to nuclear power plant operators: uranium oxide (UO2), enriched to 90% 235U. This, along with reactor core geometry changes, allowed the amount of uranium needed for the core to drop from 30 kg in the BES-5 to 11.5 kg. NaK remained the coolant, due to its low melting temperature, good thermal conductivity, and neutronic transparency. The cathode temperature in the TEU-5 was in the range of 1500-1800C, which resulted in an electrical power output of up to 10 kW.

Cesium reservoir and regulator
ENISY cesium reservoir, which is very similar to the TEU-5 system, image courtesy DOE

One of the most technically challenging parts of this reactor’s design was in the cesium management system. The metal would only be a gas inside the core, and electromagnetic pumps were used to move the liquid through a series of filters, heaters, and pipes. The purity of the cesium had a large impact on the efficiency of the thermionic elements, so a number of filters were installed, including for gaseous fission waste products, to be evacuated into space.

The first flight of the TEU-5 was on the KOSMOS-1818 satellite, launched on February 1st, 1987, onto a significantly different orbital trajectory than the rest of the US-A series of spacecraft, despite the fact that superficially it appeared to be quite similar. This was because it was the test-bed of a new type of US-A spacecraft, the US-AM, taking advantage of not only the more powerful nuclear reactor but also employing numerous other technologies. The USSR eventually announced that the spacecraft’s name was the Plasma-A, and was a technology demonstrator for a number of new systems. These included six SPT-70 Hall thrusters for maneuvering and reaction control, and a suite of electromagnetic and sun-finding sensors. Some sources indicate that part of the mission for the spacecraft was the development of a magnetospherically-based navigation system for the USSR. An additional advantage to the higher orbit of this spacecraft was that it eliminated the need for the ascent stage for the reactor core and fuel elements, saving spacecraft mass to complete its’ mission. It had an operational life of 187 days, before the reactor was placed in its graveyard orbit, and the remainder of the spacecraft was allowed to re-enter the atmosphere as its orbit decayed.

The second Plasma-A (KOSMOS-1867) launch was on July 10th, 1987. While the initial flight profile was remarkably similar to the original Plasma-A satellite, the later portions of the mission showed a much larger variation in orbital period, possibly indicating more extensive testing of the thrusters. It was operational for just over a year before it, too, was decommissioned.

Neither of the TEU-5 launches carried radar equipment aboard; but, considering the cancellation of the program also coincided with the fall of the Soviet Union, it’s possible that the increased power output of the TEU-5 would have allowed acceptable radar resolution from this higher orbit (the US-A spacecraft’s orbit was determined by the distance and power requirements of its radar system, and due to the higher aerodynamic drag also significantly limited the lifetime of each spacecraft).

After decommissioning, similar problems with NaK coolant from the reactor core were experienced with the TEU-5 reactors. There is one additional complication from the decommissioning of these larger reactor cores, however, which led to some confusion during the Solar Maximum Mission (SMM) to study solar behavior. Due to the higher operational altitude during the time that the reactor was being operated at full power, and the behavior of the materials that the reactor was made out of, what is often a minor curiosity in reactor physics caused some confusion among some astrophysical and heliophysical researchers: when some materials are bombarded by sufficiently high gamma flux, they will eject electron-positron pairs, which were then trapped in the magnetosphere of the Earth. While these radiation fluxes are minuscule, and unable to adversely affect living tissue, for scientists carefully studying solar behavior during the solar maximum the difference in the number of positrons was not only noticeable, but statistically significant. Both the SMM satellite and one other (Ginga, a Japanese X-ray telescope launched in 1987, which reentered in 1991) have been confirmed to have some instrument interference due to either the gamma wave flux or the resulting positron emissions from the two flown TEU-5 reactors. While this is a problem that only affected a very small number of missions, should astronuclear reactors become more commonly used in orbit, these types of emissions will need to be taken into account for future astrophysical missions.

The Topol program as a whole would survive the collapse of the Soviet Union, but just as with the BES-5, the TEU-5 never flew again after the Berlin Wall came down. KOSMOS-1867 was the last TEU-5 reactor, and the last US-AM satellite, to fly.

 

ENISY, The Final Soviet Reactor

The single-element thermionic reactor concept never went away. In fact, it remained in side-by-side development with the TOPOL reactor, and shared many of the basic characteristics, but was not ready in as timely a fashion as TOPOL was. The program was begun in 1967, with a total of 26 units built.

ENISY was seen to Soviet planners to be the logical extension of the TEU-5 program, and in many ways the reactor designs are linked. While the TEU-5 was designed for high-powered radar reconnaissance, the ENISY reactor was designed to be a communications and TV broadcast satellite. The amount of data that’s able to be transmitted is directly proportional to the amount of power available, and remains one of the most attractive advantages that astronuclear power plants offer to deep space probes (along with propulsion).

We’ll look at this design more in a later post, but it’s important to mention here since it is, in many ways, a direct evolution of the TEU-5. One nice thing about this reactor is that, due to the geometry of the reactor, its non-nuclear components were able to be tested as a unit without fissile fuel. Instead, induction heating units of the same size as the fuel elements could be slid into the location that the fuel rods would be for preflight testing without issues of neutron activation and material degradation due to the radiation flux.

ENISY for NEPSTP
ENISY reactor installation for NEP Space Test Program, DOE

This capability was demonstrated at the 8th US Symposium on Nuclear Energy in Albuquerque, NM, and led to the US purchasing two already-tested units from Russia (numbers V-71 and I-21U), with a buy option taken out on an additional four units, if needed. This purchase included technical information in the fuel elements, and offers of assistance from Russia to help in the fabrication of the fuel elements, but no actual fuel was sold. This reactor design would form the core of the American crewed lunar base concept in the 1990s as part of the Constellation program, as well as the core of a proposed technology demonstration mission deep space probe, but those programs never reached fruition.

We’ll look at this design in our usual depth in a couple blog posts. For now, it’s worth noting that this design reached flight-ready status; but, due to the financial situation of Russia after the collapse of the USSR, the increased availability of high-powered photovoltaic communications satellites, and the lack of funding for an American astronuclear flight test program, this reactor never achieved orbit as its predecessors did.

 

The Legacy of the USSR Astronuclear Program

 

The USSR flew more nuclear power plants than the rest of the world combined, 33 times more to be precise. Their program focused on an area of power generation that continues to hold great promise in the future, and in many ways helped define the problem for the rest of the world: in-core direct power conversion (something we’ll talk more about in the power conversion series). Even the failures of the program have taught the world much about the challenges of astronuclear design, and changed the face of what is and isn’t acceptable when it comes to flying a nuclear reactor in Earth orbit. The ENISY reactor went on to be the preferred power plant for American lunar bases for over a decade, and remains the only astronuclear design that’s been flight-certified by multiple countries.

Russia continues to build on the experience and expertise gained during the Romashka, BES-5, TEU-5, and ENISY programs. A recent test of a heat rejection system that offers far higher heat rejection capacity for its mass than any that has flown to date (a liquid droplet radiator, a concept we’ll cover in the thermal management post that will be coming up in a few months), their focus on high-power Hall thrusters, and their design for an on-orbit nuclear electric tug with a far more powerful reactor than any that we looked at today (1 MWe, depending on the power conversion system, likely between 2-5 MWt) shows that this experience has not been shoved into a closet and left to gather dust, but continues to be developed to advance the future of spaceflight.

 

More Coming Soon!

This post focused on the USSR and Russia’s astronuclear power plant expertise and operational history, a subject that very little has been written about in English (outside a number of reports, mostly focusing on the ENISY/TOPAZ-2 reactor), and is a subject that has long fascinated me. However, the USSR wasn’t the only country focusing on the idea, and wasn’t even the first to fly a reactor, just the most successful at making an astronuclear program.

The next post (which might be split into two due to the sheer number of fission power plant designs proposed in the US) is on the American programs from the same time, the Systems for Nuclear Auxiliary Propulsion, or SNAP, series of reactors (if split, the first post will cover SNAP-2, -10A, SNAPSHOT, -8, and the three reactors that evolved from SNAP-8, with SNAP50/SPUR, SABRE, SP-100, and possibly a couple more, as well as the ENISY/TOPAZ II US-USSR TSET/NEP Space Test Program/lunar base program). While the majority of the SNAP designs that were used were radioisotope thermoelectric generators, the ones that we’ll be focusing on are the fission power plants: the SNAP-2, SNAP-8, SNAP-10A (the first reactor to be launched into orbit), and the SNAP-100/SPUR reactor.

Following that, we’ll wrap up our look at the history of astronuclear electric power plants (the reactors themselves, at least) with a look at the designs proposed for the Strategic Defense Initiative (Reagan’s “Star Wars” program), return to a Russian-designed reactor which would have powered an America lunar base, had the funding for the base been available (ENISY), and the designs that rounded out the 20th century’s exploration of this fascinating and promising concept.

 

We’ll do one last post on NEP reactor cores looking at more recent designs from the last twenty years up to the present time, including the JIMO mission and a look at where Kilopower stands today, and then move on to power conversion systems in what’s likely to be another long series. As it stands that one will have a post on direct energy conversion, one on general heat engines and Stirling power conversion systems, one on Rankine cycle power conversion systems, one on Brayton cycle systems (including the ever-popular, never-realized, supercritical CO2 turbines), one on AMTEC and magnetohydrodynamic power conversion systems (possibly with a couple other non-mechanical heat engines as well), and a wrap up of the concepts, looking at which designs work best for which power levels and mission types. After that, it’ll be on to: heat rejection systems, for another multi-part series; a post on NEP ship and mission design; and, finally, one on bimodal NTR/NEP systems, looking at how to get the thrust of an NTR when it’s convenient and the efficiency of an NEP system when it’s most useful.

References

General References

http://www.buran.ru/htm/gud%2026.htm?fbclid=IwAR1jt9fsDZ10fHCSo42KUHjGTux8_uIkg43ClPrE1eg5IdQjXyhS2rSAHGY

http://www.proatom.ru/modules.php?name=News&file=print&sid=2740

https://sdelanounas.ru/blogs/29489/?fbclid=IwAR2zftn2RGOk8aU-3m1zGwNBhYMVY2zYFGUGwiorL6LSEFLNe8y-Pt4w_ag

http://elib.biblioatom.ru/text/atomnaya-energiya_t17-5_1964/go,16/?fbclid=IwAR2QzxdvVT5m3Kc3KPcVUmR5ZFrx_Er5d7RmKNFTzFz4k6-Djw_gPnnV6eA

Romashka

http://fti.neep.wisc.edu/neep602/SPRING00/lecture35.pdf

http://nacep.ru/novosti-energetiki/atomnaya-energetika/vysokotemperaturnyj-reaktor-preobrazovatel-romashka.html?fbclid=IwAR2W-9Exgyd63m6NGbVfNixGUzF9FrU2hsZUAMvdb9b75TBHQ6Ukh-EPMIA

http://nacep.ru/novosti-energetiki/atomnaya-energetika/termobatareya-romashka.html

Bouk

RORSAT page, Sven Grahn http://www.svengrahn.pp.se/trackind/RORSAT/RORSAT.html

Morning Light

The Life and Death of KOSMOS 954, Guy Weiss, courtesy Sven Grahn http://www.svengrahn.pp.se/trackind/RORSAT/cosmos954.pdf

History of the the 1035th Technical Operations Group, 1 January – 31 December 1978, via John Greenwald at The Black Vault http://documents.theblackvault.com/documents/accidents/morninglightusaf.pdf

History of the 437 Military Airlift Wing, Manning 1978, courtest John Greenwald at The Black Vault http://documents.theblackvault.com/documents/accidents/morninglight-histories.pdf

CIA Report C06607579, courtesy John Greenwald at The Black Vault http://documents.theblackvault.com/documents/cia/operationmorninglight-cia1.pdf

Topol-1

Gunther’s Space Page, PLASMA-A https://space.skyrocket.de/doc_sdat/plasma-a.htm