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AbstractThis work proposes a new propellant management configuration for an ammonia-fueled nuclear thermal propulsion system. The suggested configuration maximizes the advantage deriving from the autogenous pressurization of ammonia by exploiting the thermal power lost by the nuclear reactor toward the vacuum space due to leaking radiation. In this layout, a tank containing ammonia in saturated conditions is placed near the nuclear reactor and receives an input thermal power proportional to the dose of gamma rays and neutrons absorbed by the tank walls and the ammonia itself. Such a thermal power accelerates the vaporization process of the saturated ammonia, thus increasing the pressure in the tank. A pressure regulator valve exploits this overpressure to pressurize the ammonia propellant contained in a run tank to the level required by the mission by connecting the two ammonia volumes. The pressure achieved inside the run tank pushes the propellant with an adequate mass flow rate inside the nuclear reactor. The developed lumped parameter analysis shows how this propellant management system can provide a constant mass flow to the nuclear reactor without using a turbopump assembly. Moreover, it is shown how the proposed concept allows for a reduction in the radiation shield mass. [ABSTRACT FROM AUTHOR]

This paper analyzes the design of an alpha-decay sail. While previous studies have been conducted on the feasibility of alpha-decay sails, none have investigated the effects of different backing materials and backing material thicknesses on propulsion. This paper conducts simulations using the particle simulation toolkit Geant4 to determine the thrust produced from alpha-decay sails constructed of 238Pu and a backing layer made of aluminum, beryllium, lithium, or polyethylene. The results demonstrate that alpha-decay sails can be a very useful form of in-space propulsion, having the potential to dramatically decrease travel time beyond distances of 100 AU. [ABSTRACT FROM AUTHOR]

From 1945 to 1961, the United States spent over a billion dollars attempting to develop an airplane powered by a nuclear reactor. Such an aircraft seemingly offered nearly limitless performance capabilities, especially in terms of range, but numerous technical problems existed from the outset. The plane would have required an overly-hefty radiation shield, scientific knowledge of the involved materials was insufficient, and any plane crash would create a legitimate nuclear disaster. This article examines the nuclear plane project and what it reveals about the application (or lack thereof) of scientific knowledge by policymakers charged with developing nuclear technologies. Even though scientists and engineers were clear about the attendant technical issues, policymakers focused on the potentiality of any nuclear airplane to the detriment of the project's development and its ultimate demise. [ABSTRACT FROM AUTHOR]

After over 60 years of development, the space propulsion field in China has made tremendous progress in terms of technology system and product pedigree, and has supported major engineering applications including manned spaceflight, applied satellites, and deep space exploration. However, considering the requirements of future major aerospace missions in China, the technical level of current space propulsion systems is still insufficient, and it is urgent to plan directions for the innovative development and breakthroughs of the field. This study reviews the development status of the space propulsion systems from the aspects of electric, chemical, nuclear, and new-concept space propulsion, and analyzes the requirements of future applications. Specifically, high-performance, low-cost space propulsion systems are required to support the networking of low-Earth-orbit (LEO) small satellites; high-thrust, reusable low-temperature chemical propulsion technologies are required for new space-transportation systems; and multi-type, long-life space propulsion technologies are required for deep-space applications. The results demonstrate that the space propulsion field in China still faces multiple challenges. First, the system reliability and lifespan require further improvement. Second, the space propulsion systems of China still lag behind the advanced international level in terms of product maturity of some technologies. Third, this field typically has a high product cost. Fourth, there are few types of optional technologies, and the research progress of key technologies is lagging. Therefore, we propose the following suggestions: (1) optimizing technology options through top-level planning, (2) improving the development mechanism of the field by emphasizing basic research, and (3) clarifying and promoting scientific research and development in key technological directions, thereby achieving in-orbit applications of the propulsion systems for LEO small satellites, Earth–Moon space transfer, and deep space exploration (including manned spaceflight).

High thrust nuclear-powered spacecraft is the key technology for deep space exploration and low Earth orbit transportation in the future, the nuclear thermal propulsion system has the advantages of high specific impulse, high thrust, long operating life and repeatable start-up, which can provide reliable power support for future deep space exploration missions. Multi-element (U, Zr, Nb)C fuel is one of the selected fuels for high-power space nuclear propulsion reactors due to its high melting point, high thermal conductivity, low fission gas release rate and excellent high-temperature mechanical properties. In this paper, multi-element (U, Zr, Nb)C fuel pellets were prepared by powder metallurgy process combining carbothermal reduction and liquid phase sintering. The mechanism and influence of process parameters on reaction kinetics, phase structure, thermal conductivity and microstructure of sintered pellets were studied. The results show that according to the calculation of reaction thermodynamics, the carbothermal reduction temperatures for UO2 and Nb2O5 are 2 122 K and 1 206 K at standard pressure, respectively; Under the sintering conditions of 1 800℃, 50 MPa and 1 h, the pellet density can reach 95.5%TD by adding 0.5% metallic uranium to form liquid phase sintering, liquid phase sintering accelerates the densification process of the pellets; When the raw material M/C (M is the total metal element) is 1:6.5, the stoichiometric carbide fuel with M/C ratio of 1 can be prepared, using ZrC powders as raw materials can not only reduce the reaction temperature, but also reduce the difficulty of adjusting the M/C ratio of the reaction product; The lattice constant of (U0.2, Zr, Nb)C is slightly higher than that of (U0.1, Zr, Nb)C; The thermal conductivity of carbide fuel is related to phase composition, density and temperature; The thermal conductivity of (U0.1, Zr, Nb)C and (U0.2, Zr, Nb)C fuels increases with the increase of the content of uranium carbide, and the increase of Zr content is beneficial to the increase of the thermal conductivity of the pellets, the thermal conductivity of (U0.1, Zr, Nb)C and (U0.2, Zr, Nb)C pellets are 17.89 W/(m·K) and 18.81 W/(m·K), respectively. With the increase of sintering density, the thermal conductivity of (U, Zr, Nb)C fuels increases, and the fuels with different compositions show different thermal conductivity changing trend under the same sintering density. The thermal conductivity of (U0.1, Zr0.55, Nb0.35)C and (U0.2, Zr0.5, Nb0.3)C pellets at 90%TD relative density are 16.43 W/(m·K) and 17.90 W/(m·K), respectively, and the thermal conductivity decreases by 8.2% and 4.8% respectively compared with that at 94%TD theoretical density. The pore distribution of the pellet is relatively uniform, there is no connected open pore, and the pore size is 1-3 μm.

High thrust nuclear-powered spacecraft is the key technology for deep space exploration and low Earth orbit transportation in the future, the nuclear thermal propulsion system has the advantages of high specific impulse, high thrust, long operating life and repeatable start-up, which can provide reliable power support for future deep space exploration missions. Multi-element (U, Zr, Nb)C fuel is one of the selected fuels for high-power space nuclear propulsion reactors due to its high melting point, high thermal conductivity, low fission gas release rate and excellent high-temperature mechanical properties. In this paper, multi-element (U, Zr, Nb)C fuel pellets were prepared by powder metallurgy process combining carbothermal reduction and liquid phase sintering. The mechanism and influence of process parameters on reaction kinetics, phase structure, thermal conductivity and microstructure of sintered pellets were studied. The results show that according to the calculation of reaction thermodynamics, the carbothermal reduction temperatures for UO2 and Nb2O5 are 2 122 K and 1 206 K at standard pressure, respectively; Under the sintering conditions of 1 800℃, 50 MPa and 1 h, the pellet density can reach 95.5%TD by adding 0.5% metallic uranium to form liquid phase sintering, liquid phase sintering accelerates the densification process of the pellets; When the raw material M/C (M is the total metal element) is 1:6.5, the stoichiometric carbide fuel with M/C ratio of 1 can be prepared, using ZrC powders as raw materials can not only reduce the reaction temperature, but also reduce the difficulty of adjusting the M/C ratio of the reaction product; The lattice constant of (U0.2, Zr, Nb)C is slightly higher than that of (U0.1, Zr, Nb)C; The thermal conductivity of carbide fuel is related to phase composition, density and temperature; The thermal conductivity of (U0.1, Zr, Nb)C and (U0.2, Zr, Nb)C fuels increases with the increase of the content of uranium carbide, and the increase of Zr content is beneficial to the increase of the thermal conductivity of the pellets, the thermal conductivity of (U0.1, Zr, Nb)C and (U0.2, Zr, Nb)C pellets are 17.89 W/(m·K) and 18.81 W/(m·K), respectively. With the increase of sintering density, the thermal conductivity of (U, Zr, Nb)C fuels increases, and the fuels with different compositions show different thermal conductivity changing trend under the same sintering density. The thermal conductivity of (U0.1, Zr0.55, Nb0.35)C and (U0.2, Zr0.5, Nb0.3)C pellets at 90%TD relative density are 16.43 W/(m·K) and 17.90 W/(m·K), respectively, and the thermal conductivity decreases by 8.2% and 4.8% respectively compared with that at 94%TD theoretical density. The pore distribution of the pellet is relatively uniform, there is no connected open pore, and the pore size is 1-3 μm. [ABSTRACT FROM AUTHOR]

As part of the Artemis era of space exploration, space agencies will be working together with their industry partners to establish systems and infrastructure that enable sustained Lunar missions and develop capabilities for Mars. Lockheed Martin has a longstanding history of designing, building, and operating systems for deep space applications, from Viking to Orion. Lockheed Martin develops concepts, trades, and early system designs for Moon and Mars exploration to enable future missions. In 2016, Lockheed Martin presented a vision for achieving crewed exploration of Mars. Known as Mars Base Camp (MBC), this design reference mission envisioned a crewed vehicle in Martian orbit from which astronauts could perform excursions to Phobos and Deimos and perform telerobotic exploration of the Martian surface, including sample return. This concept served as an "existence proof" for a novel, practical, and affordable path to enable human exploration of the Martian system. In 2017, an update was published that included the production of propellant from water and a single-stage fully reusable Mars lander concept. Then in 2021, Lockheed Martin introduced a nuclear thermal propulsion (NTP) configuration of Mars Base Camp, a technology that will be greatly enabling for crewed missions to Mars. This paper matures the design of the NTP configuration of Mars Base Camp and explores the Mars mission capabilities that the NTP technology will enable. These investigations include optimized trajectories for faster transit to Mars and an analysis of abort scenarios that are made possible by the high thrust and performance of NTP. The results provide insight into the performance and capabilities that are realized when NTP technology is matured and integrated into a Mars transit vehicle. The paper will also describe initial surface infrastructure capabilities that significantly enhance sortie science operations, including mobility and power. The resulting updated Mars Base Camp serves as an example of what is possible with current technologies and technologies under development. The MBC reference mission builds on the capabilities that will be developed and demonstrated through Artemis missions, enabling a viable, sustainable long-term Mars exploration program, with the first crewed Mars mission possible in the 2030s. • Matures design of nuclear thermal propulsion configuration of crewed Mars mission • Explores Mars mission capabilities and trajectories enabled by nuclear propulsion • Describes initial infrastructure to support sustainable long-term Mars exploration [ABSTRACT FROM AUTHOR]

This paper discusses a system for Titan exploration enabled by nuclear fusion power. Titan is one of the most interesting locations in the solar system with a thick atmosphere, surface oceans, under-ice oceans and complex terrain. This paper provides a conceptual design of a fusion-powered system to explore many parts of Titan and enable the use of high-power instruments. The design includes a fusion-powered orbital transfer vehicle and an electric Titan science aircraft. A Direct Fusion Drive (DFD) propulsive engine could bring a sizable spacecraft to Titan orbit in less than two years. A second fusion reactor, configured as a closed-loop power generator, would be used for an electric Titan science aircraft. Both reactors are based on the Princeton Field-Reversed Configuration (PFRC) concept which combines an FRC with a magnetic mirror. PFRC uses a novel radio-frequency plasma heating system and deuterium-helium-3 fuel. A lower temperature plasma flows around the closed-field FRC region removing the fusion products. In the DFD propulsive configuration, this secondary flow permits direct and variable thrust and exhaust velocity. The science aircraft would do a powered entry to Titan and then have the capability to fly anywhere on the moon at subsonic speeds. The DFD-powered transfer vehicle would allow the in-orbit transfer stage to change inclination as needed to cover different areas of the surface. • A PFRC fusion rocket could deliver 1 MT payloads to Titan in about two years. • A PFRC fusion reactor could power an electric aircraft to explore Titan's surface. • Fusion power allows the aircraft to utilize novel high-power instruments. • The PFRC transfer vehicle doubles as a science platform and communications relay. [ABSTRACT FROM AUTHOR]

A human Mars mission is more challenging to astronauts than the Apollo mission because of travel time, life support requirements, and the space environment. Although plans for Mars exploration by NASA and SpaceX based on conventional rockets have been presented, there are considerations that suggest alternatives for the mid- or long-term. The purpose of this paper is to outline a fast mission enabled by advanced (nuclear) propulsion and by internationally shared technology. Whether the destination is the Mars surface or Phobos, for a chemical powered spacecraft, the round trip takes about 990 days, including a 480-day surface stay, compared to only 370 days, including a 41-day surface stay, for the nuclear-powered spacecraft assumed here. Since nuclear propulsion can provide higher speed than chemical, the radiation dose can be drastically reduced. The logistics of such a mission involve one or more cargo craft that must precede the astronauts. Ballistic entry into Mars' atmosphere depends on accurate knowledge of its features, to date poorly known, that may result in uncertainty in landing coordinates. For a single vehicle, this is not critical, but for a human crew ballistic landing kilometers away from cargo is unacceptable: walking for anything but the shortest distance cannot be afforded with current space suits. In this context, the concept of a modest L/D maneuvering cargo glider based on the past Russian "Kliper" is recommended and developed to ensure landing within a hundred meters of each spacecraft. The crewed lander vehicle is based on the high L/D, inherently stable USAF FDL-7C/D hypersonic glider experience. In a similar approach, an exploration vehicle powered by in situ manufactured CO2 and silane is described that can explore the Martian surface much faster and efficiently than with rovers or rocket-powered 'hoppers'. [ABSTRACT FROM AUTHOR]

After decades of research on low-Earth orbit, national space agencies and private entrepreneurs are investing in exploration of the Solar system. The main health risk for human space exploration is late toxicity caused by exposure to cosmic rays. On Earth, the exposure of radiation workers is regulated by dose limits and mitigated by shielding and reducing exposure times. For space travel, different international space agencies adopt different limits, recently modified as reviewed in this paper. Shielding and reduced transit time are currently the only practical solutions to maintain acceptable risks in deep space missions.

A human Mars mission is more challenging to astronauts than the Apollo mission because of travel time, life support requirements, and the space environment. Although plans for Mars exploration by NASA and SpaceX based on conventional rockets have been presented, there are considerations that suggest alternatives for the mid- or long-term. The purpose of this paper is to outline a fast mission enabled by advanced (nuclear) propulsion and by internationally shared technology. Whether the destination is the Mars surface or Phobos, for a chemical powered spacecraft, the round trip takes about 990 days, including a 480-day surface stay, compared to only 370 days, including a 41-day surface stay, for the nuclear-powered spacecraft assumed here. Since nuclear propulsion can provide higher speed than chemical, the radiation dose can be drastically reduced. The logistics of such a mission involve one or more cargo craft that must precede the astronauts. Ballistic entry into Mars’ atmosphere depends on accurate knowledge of its features, to date poorly known, that may result in uncertainty in landing coordinates. For a single vehicle, this is not critical, but for a human crew ballistic landing kilometers away from cargo is unacceptable: walking for anything but the shortest distance cannot be afforded with current space suits. In this context, the concept of a modest L/D maneuvering cargo glider based on the past Russian “Kliper” is recommended and developed to ensure landing within a hundred meters of each spacecraft. The crewed lander vehicle is based on the high L/D, inherently stable USAF FDL-7C/D hypersonic glider experience. In a similar approach, an exploration vehicle powered by in situ manufactured CO2 and silane is described that can explore the Martian surface much faster and efficiently than with rovers or rocket-powered ‘hoppers’.

We assess the possibility of reducing the travel time of a crewed mission to Mars by examining four different propulsion methods and keeping the mass at departure under 2500 t, for a fixed architecture. We evaluated representative systems of three different state of the art technologies (chemical, nuclear thermal and electric) and one advance technology, the "Pure Electro-Magnetic Thrust" (PEMT) concept (proposed by Rubbia). A mission architecture mostly based on the Design Reference Architecture 5.0 is assumed in order to estimate the mass budget, that influences the performance of the propulsion system. Pareto curves of the duration of the mission and time of flight versus mass of mission are drawn. We conclude that the ion engine technology, combined with the classical chemical engine, yields the shortest mission times for this architecture with the lowest mass and that chemical propulsion alone is the best to minimise travel time. The results obtained using the PEMT suggest that it could be a more suitable solution for farther destinations than Mars. [ABSTRACT FROM AUTHOR]

After decades of research on low-Earth orbit, national space agencies and private entrepreneurs are investing in exploration of the Solar system. The main health risk for human space exploration is late toxicity caused by exposure to cosmic rays. On Earth, the exposure of radiation workers is regulated by dose limits and mitigated by shielding and reducing exposure times. For space travel, different international space agencies adopt different limits, recently modified as reviewed in this paper. Shielding and reduced transit time are currently the only practical solutions to maintain acceptable risks in deep space missions. [ABSTRACT FROM AUTHOR]

Operating costs of merchant ships, related to fuel costs, has led the naval industry to search alternatives to the current technologies of propulsion power. A possibility is to employ nuclear reactors like the Russian KLT-40S, which is a pressurized water reactor (PWR) and has experience on civilian surface vessels. However, space and weight are critical factors in a nuclear propulsion project, in addition to operational safety and costs. This work aims at comparing molten salt reactors (MSR) with PWR for merchant ship propulsion. The present study develops a qualitative analysis on weight, volume, overnight costs, fuel costs and nuclear safety. This work compares the architecture and operational conditions of these two types of reactors. The result is that MSR may produce lower amounts of high-activity nuclear tailings and, if it adopts the 233U-thorium cycle, it may have lower risks of proliferating nuclear weapons. Besides proliferation issues, this 4th generation reactor may have lower weight, occupy less space, and achieve the same levels of safety with less investment. Thus, molten salt regenerative reactors using the 233U-thorium cycle are potential candidates for use in ship propulsion.

This paper describes the development of an Australian roadmap for the acquisition of nuclear propulsion for submarines and selected other vessels. This paper reports on the goals of the working group and an outline of the projected roadmap. Australia first operated naval submarines in 1914 and has maintained amodern fleet continuously since 1967. Now embarking on the third generation of conventionally powered boats, attention is shifting to nuclear propulsion for future generations. Nuclear propulsion confers two significant advantages on anaval submarine: increased speed for sustained periods and removal of the requirement for periodic recharging of batteries using air-breathing diesel generators. Development of the nuclear propulsion roadmap is being undertaken by avoluntary working group of nuclear scientists, submarine designers, builders, operators and maintainers, and multidisciplinary engineering and project management professionals, following asystems engineering, disciplined approach to consider all possible options for essential infrastructure, safety assurance, workforce training and development, economic and geopolitical constraints. [ABSTRACT FROM AUTHOR]

The main purpose of this work is to perform an analysis of realistic new trajectories for a robotic mission to Saturn's largest moon, Titan, in order to demonstrate the great advantages related to the Direct Fusion Drive (DFD). The DFD is a D - 2 3 He fueled, aneutronic, thermonuclear fusion propulsion system (Cohen et al., 2019). This fusion propulsion concept is based on a magnetically confined field reversed configuration plasma, where the deuterium propellant is heated by fusion products, and then expanded into a magnetic nozzle, providing both thrust and electrical energy to the spacecraft. The trajectories calculations and analysis for the Titan mission are obtained based on the characteristics provided by the PPPL (Cohen et al., 2019) for a 2 MW-class DFD engine. Two different profile missions are considered: the first one is a thrust–coast–thrust profile with constant thrust and specific impulse, the second scenario is a continuous and constant thrust profile mission. Each mission study is divided into four different phases, starting from the initial low Earth orbit departure, the interplanetary trajectory, Saturn orbit insertion, and the Titan orbit insertion. For all mission phases, maneuver time and propellant consumption are calculated. The results of calculations and mission analysis offer a complete overview of the advantages in term of payload mass and travel time. It is important to emphasize that the deceleration capability is one of the DFD game changers: in fact, the DFD performance allows to rapidly reach high velocities and decelerate in even shorter time period. This capability results in a total trip duration of 2.6 years for the thrust–coast–thrust profile and less than 2 years for the continuous thrust profile. The high payload enabling capability, combined with the huge electrical power available from the fusion reactor leads to a tremendous advantage compared to present technology. • The Direct Fusion Drive (DFD) is based on the D-3He nuclear fusion reaction. • A thrust–coast–thrust profile for an Earth–Titan mission is studied. • A continuous thrust profile for an Earth–Titan mission is studied. • A total trip duration is 2.6 years for the thrust–coast–thrust profile mission. • A total trip duration is less than 2 years for the continuous thrust profile mission. [ABSTRACT FROM AUTHOR]

The concept of implementation of environmental health protection and sustainment in aerospace environments by definition implies a One Health systems approach. One Health indicates an inherently complex, contextually interrelated system with consideration of human, animal, plant, systems engineering, and environmental health, their interrelationships, and networks. One Health implies seamless integration of subsystem co-dependencies to achieve an outcome of overall health protection for the individual. One of the most challenging aspects of space travel involves prevention, mitigation and protection from radiation injuries. While avoidance altogether is the best approach, these authors will focus on minimized exposure through limiting time in the space radiation environment in the transit to Mars and back. Implementation of the pillars of time, distance and shielding comprise ALARA, “As Low as Reasonably Achievable” (www.cdc.gov/nceh/radiation/alara.html) and is stressed in this strategy. This general overview will briefly describe the critical components of space environmental health in anticipation of increasing duration and interaction of human, animal, and plant habitation of aerospace and extreme environments into the future. Of the many considerations that could be addressed, precision medicine, and bioinformatics are the most rapidly evolving. Complex interdependencies will emerge from macro- and micro-environmental ecosystems data analysis, not yet fully comprehended or understood in the context of space health. We will conclude this contribution with suggested new countermeasure strategies gleaned through big data analytics that may protect space crew through mitigation of radiation exposure in flight.

For the human species and its unique culture to survive the death of the sun, a bridge must be built to other solar systems with earthlike planets. The Kepler space telescope has discovered a large number of extrasolar planets, but only a few with earthlike conditions, and those are many light years away. Assuming that no new fundamental laws of physics which would greatly facilitate interstellar spaceflight are awaiting discovery, one can only see two avenues: First, at 10% of the speed of light via deuterium fusion bomb propulsion, harvesting the deuterium in the comets of the Oort clouds surrounding our and other suns, and by hopping from comet to comet. Second, with relativistic velocities by matter-antimatter generated GeV laser beams released from relativistically stabilized hydrogen-antihydrogen super-pinch discharges, transmitting the recoil of the laser beam by the Mössbauer effect to the spacecraft. The production of the anti-hydrogen can be done with solar energy in robotic factories on the planet Mercury. For the first, but much more for the second possibility, very large masses must be lifted in one stage into low Earth orbit. This can conceivably be done by chemically ignited pulsed pure fusion bomb propulsion. • Fusion propulsion. • Fissionless ignition. • Fast manned interplanetary spaceflight. [ABSTRACT FROM AUTHOR]

Highlights • The free gas approximation approach introduced significant error by about 2000 pcm in PBR reactor. • The systematic temperature effect study was made through LiH thermal effects of kernel, expansion and dissociation. • The mixed moderator method was designed to reduce or resolve the positive moderator temperature effect. Abstract Due to the thermalization of lithium hydride (LiH) in nuclear propulsion particle bed reactor (PBR), thermal-kernel effect of LiH and its impact on the reactivity of PBR was studied. The phonon properties of LiH have been analyzed by the first-principles simulations using the VASP and PHONON codes. Applying the generated phonon density of states, the ACE-format thermal-neutron cross-section library of LiH has been generated by NJOY code. Neutronic modeling and simulation of PBR were done in this paper. The impact of LiH thermalization on the reactivity feedback of PBR was studied and analyzed. From the numerical results, it can be observed that the thermal effect of LiH was positive to the reactivity of PBR. The approximation of the free-gas model introduces significant error over 2000 pcm (10−5). In order to find the thermal mechanism of LiH, detailed research and analysis towards the thermal expansion and thermal dissociation have been also done. It was found that the thermal-kernel effect finally made the most contribution. In order to improve the safety of PBR reactor, the mixed moderator method was designed to reduce or resolve the positive moderator temperature effect. [ABSTRACT FROM AUTHOR]

The article focuses on the production of nuclear power in Denmark. Denmark has sufficient expertise to operate nuclear power plants. The country did not produce nuclear power during the 1960s and 1970s. A nuclear reactor research laboratory was established in the country in the year 1957. A plan to install about 14,000 megawatts of nuclear power in Elsam, Denmark before the year 2000 was designed in the year 1973. The construction of two nuclear reactors in the country began in the year 1970. The reactors became operational in the years 1975 and 1977.

The author reflects on the possibility of the utilization atomic power for the U.S. aircrafts. He argues that the difficulty in having aircraft powered by atomic energy depends on the thermodynamics efficiency in utilizing the great energies, compactness of reactors, physical properties of the materials and the nuclear properties of the materials. He stated that the availability of nuclear-powered aircraft depends on how rapidly the work progresses.

The 2010s witnessed a renewal in international interest of space operations extending outside geosynchronous orbit to encompass the cislunar environment and beyond with invigorated U.S., Chinese, and Russian lunar mission initiatives; planned commercial lunar projects; and coalescing international efforts to reach Mars and push deeper into the Solar System. With the space beyond the near-Earth orbital regimes likely to become competitive and congested in the coming decades, reliable and high-yield means of generating power and propulsion will be needed to enhance mission assurance and operational responsiveness. Nuclear systems represent a promising technology with a rich heritage and provenance of space-based applications to satisfy emerging requirements for electrical power and propulsive impulse for long-term human development of the Earth-Moon system and its planetary neighbors. In this work, an atlas for defining the varying historical or proposed uses of nuclear power in space operations and exploration is presented according to spatial zone within the Earth-Moon and wider Solar System. Depending on the spatial zone, nuclear power will be discussed with respect to applications such as electrical power generation, propulsion, resource extraction, and weapon testing and employment for the space control and planetary defense missions. [ABSTRACT FROM AUTHOR]

Although the harsh space environment imposes many severe challenges to space pioneers, space exploration is a realistic and profitable goal for long-term humanity survival. One of the viable and promising options to overcome the harsh environment of space is nuclear propulsion. Particularly, the Nuclear Thermal Rocket (NTR) is a leading candidate for near-term human missions to Mars and beyond due to its relatively high thrust and efficiency. Traditional NTR designs use typically high power reactors with fast or epithermal neutron spectrums to simplify core design and to maximize thrust. In parallel there are a series of new NTR designs with lower thrust and higher efficiency, designed to enhance mission versatility and safety through the use of redundant engines (when used in a clustered engine arrangement) for future commercialization. This paper proposes a new NTR design of the second design philosophy, Korea Advanced NUclear Thermal Engine Rocket (KANUTER), for future space applications. The KANUTER consists of an Extremely High Temperature Gas cooled Reactor (EHTGR) utilizing hydrogen propellant, a propulsion system, and an optional electricity generation system to provide propulsion as well as electricity generation. The innovatively small engine has the characteristics of high efficiency, being compact and lightweight, and bimodal capability. The notable characteristics result from the moderated EHTGR design, uniquely utilizing the integrated fuel element with an ultra heat-resistant carbide fuel, an efficient metal hydride moderator, protectively cooling channels and an individual pressure tube in an all-in-one package. The EHTGR can be bimodally operated in a propulsion mode of 100 MWth and an electricity generation mode of 100 kWth, equipped with a dynamic energy conversion system. To investigate the design features of the new reactor and to estimate referential engine performance, a preliminary design study in terms of neutronics and thermohydraulics was carried out. The result indicates that the innovative design has great potential for high propellant efficiency and thrust-to-weight of engine ratio, compared with the existing NTR designs. However, the build-up of fission products in fuel has a significant impact on the bimodal operation of the moderated reactor such as xenon-induced dead time. This issue can be overcome by building in excess reactivity and control margin for the reactor design.

Global marine shipping annually accounts for about one billion tonnes of CO 2 equivalent greenhouse gas emissions. Nuclear power propulsion may be an option to de-carbonise some niches of the merchant ocean fleet. This paper considers the three experimental nuclear-powered merchant ships launched and operated in the world so far; the iconic Savannah (USA), Otto Hahn (West Germany) and Mutsu (Japan). They were independently developed and operated in the 1960s and 1970s for technology demonstration and learning. A fourth ship, Sevmorput (Soviet Union/Russia, 1988–to date), is a pioneer in respect of its logistics functions and propulsion system. This paper develops a theoretical framework for the sustainability assessment of nuclear propulsion in ocean merchant shipping and presents a method for exploring nuclear propulsion, relative to flag state, ports, shipping resources and ocean transport services. The experimental ships’ transport efficiency is discussed and related to contemporary oil-fired shipping of general cargo, and to recent literature presenting possible future applications of merchant nuclear propulsion in some market niches. Insights provided include: (1) the experiments demonstrate that merchant nuclear propulsion may be technically feasible; (2) port and canal access for merchant nuclear-powered ships may be difficult and restricted; (3) the up-front costs, refuelling and end-of-life decommissioning costs of nuclear-powered ships are vast and uncertain against conventionally-powered ships; (4) because nuclear fuel is comparatively low-cost, the conventional oil-fired ship cost implications of high-speed operations do not apply. [ABSTRACT FROM AUTHOR]

Reports on the nuclear propulsion and power generation program called Project Prometheus by the U.S. National Aeronautics and Space Administration. Description of the project; Budget allocated for the project; Concept of the nuclear propulsion.