Engineering topics
Matthew Duchek
Publications and source records attributed to Matthew Duchek.
Hybrid NEP-Chemical Vehicle and Propulsion Technology Study for Crewed Mars Missions
Nuclear Electric Propulsion (NEP) is a suite of technologies with the potential to enable crewed opposition-class missions to Mars. Each subsystem comprising an NEP system has multiple technology options that present tradeoffs in vehicle sizing and technology development risk. Multiple vehicle concepts have been studied in the past and are currently being studied at NASA. Three models have been developed to illustrate the impact of key technology parameters on overall sizing for a crewed Mars transportation vehicle. Vehicle mass required to close the mission as a function of NEP system alpha (kWe/kg) and specific impulse (Isp) is estimated with a detailed trajectory model. A power system mass model estimates alpha as a function of power and radiator mass assumption. A power conversion system thermodynamic model predicts the radiator area required to close a Brayton cycle power conversion system. Combined with the architecture mass required for mission closure, the radiator area and alpha model provide insight into how technology development may impact the mission. Our focus is on parametric sweeps of the whole design space rather than any particular point design. Results from the mission model comparing electric propulsion technology (Hall, Ion, Magnetoplasmadynamic) and both 2039 and 2042 opposition-class mission launch windows are included. The results of the study illustrate the technology parameters that can result in mission closure and illustrate where the architecture is sensitive to variations in technology performance or requirements.
Sensitivity of Hybrid NEP-Chemical Vehicle Mass to Assumptions for Crewed Opposition-Class Mars Missions
This research illustrates the impact of different technology choices and their associated performance on overall sizing for a hybrid Nuclear Electric Propulsion (NEP) and chemical crewed Mars transportation vehicle. A set of models for the trajectory and vehicle mass, power system specific mass(α), and power conversion performance enable the analysis. Vehicle mass required to close the mission is calculated as a function of α and specific impulse (Isp) for multiple choices of high-level assumptions including system alpha vs. power scaling and electric thruster type. System alpha is built up and compared for multiple cases of technology assumptions. A Brayton cycle model is used to illustrate the alpha sensitivities to assumptions in cycle design such as peak operating temperature and component performance. The analysis illustrates how technology performance sensitivities affect the alpha and thus vehicle sizing for a range of mission and technology assumptions.
Nuclear Electric Propulsion Modular Power Conversion Model
This work builds upon a previously examined single loop power conversion cycle for nuclear electric propulsion systems. The intent of this model is to enable examination of trends within the system and extract system parameters that could be used in a mass model to understand how technology performance may impact overall system mass.Several model upgrades were made since the previous work which included physics-based sizing of the turbomachinery and pressure loss inside the radiator. A higher fidelity and modular fluid property code was also developed to help understand the impact of variable fluid properties more accurately and allow for the analysis of different fluids in the same model. The upgraded model features radiator and reactor loops with separate fluids from the Brayton cycle to understand advantages and disadvantages of using multiple working fluids as well as the capability of simulating off nominal system performance. The latter provides a steppingstone for modeling the transient performance of the power conversion system.
Mass Modeling of NEP Power Conversion Concepts for Human Mars Exploration
The specific mass (mass per unit of electric power output) of an NEP power conversion system is an important metric for the performance and feasibility of a crewed NEP vehicle. This work explores a component level buildup of the specific mass for a crewed NEP vehicle. The buildup is highly parametric and avoids being tied to specific technologies where practical. This allows the specific mass to be calculated for a variety of assumptions and operating conditions and be used to optimize particular design variables or compare different system configurations. The values of specific mass are dependent on assumptions with significant uncertainty; comparison between cases and trends observed in the models are the main goal of the work presented here. To demonstrate the level of insight this type of modeling can provide, the impacts of compressor inlet temperature, turbine inlet temperature, and radiator pressure drop on specific mass are explored. In addition, the specific mass can be used to assess the benefit of separating the radiator and reactor loop from the power conversion cycle.
Brayton Cycle Power Conversion Model for MW-Class Nuclear Electric Propulsion Mars Missions
A Brayton cycle based power conversion system for a nuclear electric propulsion application was modeled in Simulink as part of NASA’s space nuclear program in order to explore the impact of technology assumptions on the power conversion system performance and capabilities. The thermodynamic processes and algorithms within the model are documented, including a higher fidelity reactor model. Assumptions are chosen based on literature and subject matter expert review, and example results and capabilities of the model are shown. The effects of the turbine inlet and compressor inlet temperature on radiator area and thermal efficiency are discussed. For a He-Xe closed Brayton cycle, radiator areas as low as 650 m2/MWe are shown, with corresponding thermal efficiences at roughly 20% for the minimal radiator area solutions.
Nuclear Electric Propulsion Brayton Power Conversion Working Fluid Considerations
NASA has considered Nuclear Electric Propulsion (NEP) for high ∆V missions since the late 1950s, but the current technology readiness level of the requisite power-train needs to be raised for such a mission. The powertrain includes reactor, power conversion, power management, electric propulsion, and thermal management components that must be integrated to minimize system a (kg/kWe) and to finalize a propulsion system architecture within the 2025-2027 timeframe requires advancing these component technologies to technology readiness level (TRL) 5 and Advancement Degree of Difficulty (AD2) 3 in an expeditious manner with minimal risks. This paper will only address the power conversion (heat to electric) components of that system. Based on both internal and industry studies, a primary conclusion of this work is that a single-spool supercritical Xe-He radial flux Brayton heat engine combined with a permanent magnet synchronous alternator can potentially be developed with the least technical risk to meet the technology readiness schedule and required NEP system performance metrics.
Nuclear Electric Propulsion Brayton Power Conversion Working Fluid Considerations
NASA has considered Nuclear Electric Propulsion (NEP) for high V missions since the late 1950’s, but the current technology readiness level of the requisite powertrain needs to be raised for such a mission. The powertrain includes reactor, power conversion, power management, electric propulsion, and thermal management components that must be integrated to minimize system (kg/kWe) and to finalize a propulsion system architecture within the 2025-2027 timeframe requires advancing these component technologies to technology readiness level (TRL) 5 and Advancement Degree of Difficulty (AD2) 3 in an expeditious manner with minimal risks. This paper will only address the power conversion (heat to electric) components of that system. Based on both internal and industry studies, a primary conclusion of this work is that a single-spool supercritical Xe-He radial flux Brayton heat engine combined with a permanent magnet synchronous alternator can potentially be developed with the least technical risk to meet the technology readiness schedule and required NEP system performance metrics.
Nuclear Electric Propulsion Modular Power Conversion Model
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Mass Modeling of NEP Power Conversion Concepts for Human Mars Exploration
The specific mass (mass per unit of electric power output) of an NEP power conversion system is an important metric for the performance and feasibility of a crewed NEP vehicle. This work explores a component level buildup of the specific mass for a crewed NEP vehicle. The buildup is highly parametric and avoids being tied to specific technologies where practical. This allows the specific mass to be calculated for a variety of assumptions and operating conditions and be used to optimize particular design variables or compare different system configurations. The values of specific mass are dependent on assumptions with significant uncertainty; comparison between cases and trends observed in the models are the main goal of the work presented here. To demonstrate the level of insight this type of modeling can provide, the impacts of compressor inlet temperature, turbine inlet temperature, and radiator pressure drop on specific mass are explored. In addition, the specific mass can be used to assess the benefit of separating the radiator and reactor loop from the power conversion cycle.
Brayton Cycle Power Conversion Model for MW-Class Nuclear Electric Propulsion Mars Missions
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Evaluating the Performance of Hybrid Vehicles between LEO, Cislunar Space, and Mars
Nuclear power and electric propulsion technologies can enable a broad range of existing and future space mission concepts. This paper evaluates how these two technology classes, when combined into systems with various performance levels (and paired with a chemical propulsion system) affect vehicle sizing and mission feasibility for round-trip, opposition-class, crewed missions to Mars. The technology trade-space evaluated in this paper encompasses: various nuclear power system mass-efficiency levels (or power-specific mass), a range of output power levels available to the electric propulsion system, two electric propulsion thruster technologies (Hall and Magnetoplasmadynamic) at various characteristic specific impulse levels, and a range of propellant tank mass sizing coefficient. Each combination of the technologies is evaluated for the 2039 and the 2042 Mars mission opportunities for a range of imposed total mission duration constraints. The results show that synergies between technology performance levels exist and that increasing the performance of some parameters might have undesired consequences for the trajectory and vehicle. It was found that increasing the mass-efficiency of the nuclear power system is broadly beneficial, resulting in lower vehicle masses and enabling shorter mission durations. However, increasing the specific impulse of a thruster or increasing the available power level do not always yield a net benefit to the vehicle or mission; since increasing the specific impulse or power level (holding power system mass-efficiency constant) tends to decrease the vehicle thrust-to-mass ratio. Furthermore, the results show that mission feasibility is highly dependent on the mission duration; the required technology performance level to enable a mission is relaxed as the mission duration increases. Given the optimally sized vehicles resulting from the trade-space for a crewed mission to Mars, this paper also evaluates the impact of aggregating the Mars mission vehicle in Low-Earth Orbit and transferring it to the Mars mission departure node (using the on-board power and propulsion systems). The trade-space for this portion of the analysis includes the option of in-space vehicle refueling at the Mars mission departure node. The results show that on-orbit refueling can relax the required technology performance levels to achieve lower launch masses and orbit-raising durations at the cost of increased architecture complexity and risk.
Evaluating the Performance of Hybrid Vehicles between LEO, Cislunar Space, and Mars
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Heat Pipe Heat Exchanger for Nuclear Electric Propulsion Power Conversion System
Heat pipe reactors have been considered by the Space Nuclear Propulsion program for Nuclear Electric Propulsion (NEP) power conversion systems and will require the use of heat exchangers to transfer heat via heat pipes to the Brayton working fluid from the reactor. Sodium (Na) and lithium (Li) were considered as viable working fluids inside the heat pipes which were assumed to have the same geometry based on studies and information from the Los Alamos National Laboratory. The heat exchanger was assumed to be a rectangular duct with heat pipes serving as tubes from previous NEP work and recommendations. Based on this geometry, Zukauskas correlations were used to model the convective heat transfer and pressure losses. Parametric sizing of the reactor component involved operational limits-based heat pipe thermal hydraulic modeling in cohesion with required user input geometry for the in-core lattice and various subcomponents. This work considered various power conversion inlet temperatures (PCIT) of 1100 K, 1150 K, and 1200 K for Na heat pipes and 1100 K, 1150 K, 1200 K, and 1400 K for Li heat pipes based on recommendations from prior work. Using these different PCITs, the subsystem masses and pressure losses were determined and analyzed. Na showed a lower overall operating temperature and about a fifth of the maximum heat throughput capability than that of Li for the same geometry. Due to this, the entire Na-based subsystem ended up being three times more massive than the Li-based subsystem given five times the required number of heat pipes. At the low PCIT of 1100 K, the Na-based subsystem exhibited the lowest pressure losses given the large overall cross sectional flow area and relatively low frictional pressure losses. However, as the PCIT increased, the frictional pressure losses increased resulting in higher pressure losses at the 1200 K PCIT than Li-based subsystem. However, the Li-based subsystem exhibited the largest pressure losses of all analyzed cases at the 1400 K PCIT due to the low density of the Brayton working fluid at this temperature.
Heat Pipe Heat Exchanger for Nuclear Electric Propulsion Power Conversion System
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Coupled Reactor Multiphysics and Mass Scalability Assessment for Crewed Megawatt-Class NEP System Architectures
Nuclear Electric Propulsion (NEP) is an in-space propulsion technology capable of enabling opposition and conjunction class crewed Mars missions. NEP subsystems include the reactor for heat generation, a power conversion system (PCS), power management and distribution (PMAD), electric propulsion subsystem (EPS), and a primary heat rejection system. Specific mass, or αe (kg / kWe), is a key performance parameter (KPP) of the propulsion system which is directly scalable with the performance and mass estimates for individual components. To inform technology maturation planning, full system and component level parametric modeling is ongoing to explore the design trade space and illustrate the effect of subsystem design choices on the system KPPs. In this study, scaling of high-assay, low-enriched uranium (HALEU) reactor designs is assessed through coupled reactor physics and thermal hydraulics analyses. Scaling analyses evaluate the impact of system performance parameters (power level, interface temperatures) on mass for direct gas cooled, pumped liquid metal, and passively cooled heat pipe reactor concepts. Each concept requires specific geometries and working fluids to reach the performance goals of PCS interface conditions (temperature, pressure, flow rate) and system mass. The reactor assembly includes the active core (fuel, moderator, cladding, working fluid), axial and radial neutron reflectors, control drums, structural support / pressure vessel, and external radiation shielding. Each of these components are parametrically sized based on performance parameters for a megawatt-class power cycle. Results of this scaling analysis increase NEP propulsion system modeling fidelity and ultimately aim to support technology down-selection along with related technology development planning. The reactor and shield αe are a function of several PCS design choices, and reactor scaling with these parameters must be considered to enable an informed decision on reactor geometry and working fluid combination.
Coupled Reactor Multiphysics and Mass Scalability Assessment for Crewed Megawatt-Class NEP System Architectures
Nuclear Electric Propulsion (NEP) is an in-space propulsion technology capable of enabling opposition and conjunction class crewed Mars missions. NEP subsystems include the reactor for heat generation, a power conversion system (PCS), power management and distribution, electric propulsion system, and heat rejection system. Specific mass, or α (kg/kWe), is a key performance parameter (KPP) of the propulsion system which is directly scalable with the performance and mass predictions for each individual component. To inform technology maturation planning activities, full system and component level parametric modeling is ongoing to explore the design trade space and illustrate the effect of subsystem design choices on the system KPPs. In this study, scaling of high-assay, low-enriched uranium reactor designs is assessed through coupled reactor physics and thermal hydraulics analyses. Scaling analyses evaluate the impact of system performance parameters (power level, interface temperatures) on mass for direct gas cooled, pumped liquid metal, and passively-cooled heat pipe reactor concepts. Each concept requires specific geometries, fluids, and power conversion interface conditions (temperature, pressure, flow rate) to meet desired performance and mass. The reactor assembly includes the active core (fuel, moderator, cladding, working fluid), axial and radial neutron reflectors, control drums, structural support / pressure vessel, and external radiation shielding. Each of these components are parametrically sized based on performance parameters for a megawatt-class power cycle. Results of this scaling analysis increase NEP propulsion system modeling fidelity and ultimately aim to support concept down-selection along with related technology development planning. The reactor and shield α are a function of several PCS and heat rejection system design choices, and reactor scaling with these parameters must be considered to enable an informed decision on an optimal reactor geometry and working fluid combination.