The future of crewed deep space exploration requires advanced system awareness and monitoring techniques to ensure the reliability of critical subsystems such as the electric power system (EPS). Currently, expert systems are used to detect and isolate large abrupt faults such as short circuits are sufficient to safe the power system. More nuanced and subtle fault behavior is analyzed by ground control, where corrective and troubleshooting actions can be made remotely or by the onboard crew. To ensure the safety of the crew, onboard computers are tasked with the detection and diagnosis of faults and disturbances onboard the vehicle. Spacecraft experience additional failure modes on a regular basis after launch that were unplanned, unexpected, or ambiguous, and NASA has identified improved software as a means of lowering the number of failures onboard spacecraft. This paper proposes a novel combination of model-based and data-driven techniques to monitor and identify known normal, faulty, and anomalous behavior. The method is demonstrated against a high-fidelity simulation of the spacecraft EPS and validated against real hardware.

The future of deep space exploration is becoming increasingly dependent on a reliable and resilient electric power system (EPS) to support several subsystems including life support, electric propulsion, autonomous rovers, and more. The planned growth of NASA’s Artemis base camp will present new challenges in the operation and control of the expanding EPS. In particular, improved fault detection and isolation methods are needed to protect the microgrid from faults as it undergoes expansion and modifications given the limitations and constraints of a space-based power system. This paper proposes a pragmatic technique for achieving coordinated zonal protection against direct current (DC) line-to-ground faults with autonomous adaptive tuning for topological and operational changes to the EPS. Here a dynamic method is developed to tune circuit breaker settings based on the given system topology, generation capacity, and expected load. The proposed adaptive coordinated protection approach is demonstrated using real-time simulation and hardware-in-the-loop (HIL) experiments to evaluate its effectiveness in achieving zonal fault isolation.

The future of deep space exploration requires high levels of reliability in critical subsystems such as the electrical power system. This paper provides an analysis of voltage stability of direct current (DC) microgrids for spacecraft applications. Bifurcation theory is used to determine the behavior of the system and identify the major causes of voltage instability. The analytical results of the bifurcation model are experimentally verified through a series of tests emulating probable operating conditions of the spacecraft. The findings of this paper are applicable to similar classes of islanded (grid forming) DC electric power systems including aerospace vehicles, shipboard systems, and terrestrial microgrids.

NASA's Artemis Program outlines the need for a lunar habitat capable of sustaining human life as well as mining and producing raw materials on the lunar surface. This mission is a means towards deeper space exploration, with plans for reaching Mars and beyond. Human presence on the moon is not possible without the ability to generate and distribute energy, namely electricity, through a network of sources, loads, and power converters known as a microgrid. Multiple microgrids can be deployed on the moon based on location and need with interconnections to increase resiliency and reliability. A method for adaptive control through power converters connecting two DC microgrids is proposed.

Hybrid-electric architectures are a promising means to achieve clean and efficient aircraft propulsion needed for small, short-range electric vertical takeoff and landing (eVTOL) class vehicles. This paper explores the design space for a six-passenger quadrotor hybrid-electric propulsion system and shows that hybrid architectures that are more efficient than engine-only architectures can be built with near-term battery technology (~150 Wh/kg at the pack level). Data obtained shows that hybrid-electric propulsion systems can achieve 28% block fuel reduction and 27% total energy cost savings over a 120 nautical mile (nmi) mission compared to conventional turboshaft architectures. This work suggests that hybrids are likely the most efficient architectures that can be produced in the near term for this class of vehicle and motivates further development in this area.

As interest in space exploration grows, developing a lunar habitat has become a key component of extending missions into deep space. To guarantee reliable power management of a lunar habitat's DC microgrid, control schemes are needed that can manage the different assets (batteries, photovoltaics, loads) effectively. Proposed hierarchical control schemes are further developed into hardware solutions using Opal-RT's real-time simulation software and Power Hardware-in-the-Loop platform. Experimental results of a simulated DC microgrid and physical DC/DC components can allow better realization and performance of applications such as battery discharge control.

for a specific site and provides solutions to those challenges. The paper also presents the controller/power-hardware-in-the-loop evaluation platform built to suit the needs of the microgrid as well as the IEEE 2030.8 consistent test cases used to evaluate the proper operation of the microgrid controller. Finally, the paper presents the results from a subset of the experiments performed to evaluate the microgrid controller. a microgrid controller for a site because of the unique requirements presented by the controllable and uncontrollable elements in the system. There are also challenges to testing the performance of the microgrid controller for such unique microgrids. The research presented here discusses the challenges to evaluating a microgrid controller for a specific site and provides solutions to those challenges. The paper also presents the controller/power-hardware-in-the-loop evaluation platform built to suit the needs of the microgrid as well as the IEEE 2030.8 consistent test cases used to evaluate the proper operation of the microgrid controller. Finally, the paper presents the results from a subset of the experiments performed to evaluate the microgrid controller.

This paper presents a novel hierarchical control approach of a DC microgrid (DCMG) which is supplied by a distributed battery energy storage system (BESS). With this approach, all battery units distributed in the BESS can be controlled to discharge with accurate current sharing and state-of-charge (SoC) balancing. Similar to other hierarchical control approaches used in DCMGs, this approach consists of three levels: (1) primary control, (2) secondary control, and (3) tertiary control. This work includes defining a unit control error (UCE) at the secondary control level and evaluating current sharing weights at tertiary control level. A centralized controller at secondary control level is designed to detect the UCEs of each battery unit, and to restore the average voltage of a DCMG and control battery current sharing simultaneously. The distributed battery units share the load current in a DCMG based on weights. These weights are evaluated at the tertiary control level based on battery SoCs. The approach’s effectiveness was confirmed in digital simulation tests with the same simulation model as used in the NASA AMPS Modular Hardware Emulator.

This paper considers a hybrid electric propulsion architecture where most of the electric power is transmitted from the generator to the motors without conversion. Doubly fed induction machines are chosen for generation and propulsion, due to their ability to operate over a range of speeds using reduced-size power converters. The focus of this paper is on the presentation and demonstration of a strategy that allows for the stable and independent operation of multiple motors using the power produced by a single generator. The control methodology includes synchronization, soft-start, and closed-loop speed control of each motor as a means of controlling output thrust. The validation is carried out on a low-power test bed using fractional horsepower machines. The success obtained at a small-scale suggests that the proposed strategy would be worth evaluating at higher power levels, with a potential application to commercial transport aircraft.

There is a high degree of research interest in the design space for electric vertical takeoff and landing (eVTOL) vehicles, because these vehicles are seen as key enablers for urban air mobility. This work further explores the eVTOL design space, by presenting an analysis of a six-passenger eVTOL quadrotor powertrain, with integrated power, propulsion, and thermal management systems modeled using the Numerical Propulsion System Simulation (NPSS) and the NPSS Power System Library. Four powertrain architectures are modeled at the same design point and compared over a design mission. Results from an architecture trade study show that a hybrid architecture performs best in terms of range, however, the hybrid needs batteries with high specific energy and specific power in order to obtain a benefit over turboelectric architectures. Parameteric sensitivity studies are conducted to determine correlations between component parameters and system metrics. This data provides useful indicators for further technological improvement. Lastly an initial TMS model is presented, and sensitivity studies on TMS design parameters are presented as well, to show high level TMS design trends.

The paper considers a hybrid electric propulsion architecture where most of the electric power is transmitted from the generator to the motors without conversion. Doubly-fed induction machines are chosen for generation and propulsion, due to their ability to operate over a range of speeds using reduced-size power converters. The focus of the paper is on the presentation and demonstration of a strategy that allows for the stable and independent operation of multiple motors using the power produced by a single generator. The control methodology includes synchronization, soft-start, and closed-loop speed control of each motor as a means of controlling output thrust. The validation is carried out on a low power test bed using fractional horsepower machines. The success obtained at a small scale suggests that the proposed strategy would be worth evaluating at higher power levels, with a potential application to commercial transport aircraft.

A variety of electrified aircraft propulsion (EAP) concepts have been proposed to address the economic and environmental challenges faced by the commercial aviation industry. Proper tools are needed in order to answer outstanding questions concerning these concepts, particularly about the electrical power systems that enable them. For instance, questions remain regarding which power system architectures are best for which vehicle, what component modifications will have the greatest return on investment, and how efficient or heavy a given concept power system will be. The Electrical Power System - Simulation and Analysis Tool (EPS-SAT) has been developed in order to answer these questions. Further, EPS-SAT promises to be applicable for power systems in domains beyond EAP, including terrestrial grids, space vehicles, and permanent space installations.

Electrified aircraft propulsion seeks to address ambitious goals in the commercial airline industry, including significant decreases in fuel burn, emissions, noise, and takeoff field length. In order to move these electrified propulsion concepts forward, analysis tools are needed that can model propulsion systems containing both gas turbine and power system components. This work presents the definition of an electric port, a set of electrical power systems tools, and simulation examples for the Numerical Propulsion System Simulation (NPSS) software. NPSS is the industry standard modeling and simulation package for aircraft propulsion systems, and the ability to design, size, integrate, and analyze electric power systems will enable industry efforts towards the development of electrified aircraft propulsion.

Improving protection and health monitoring capabilities onboard the electrical power system (EPS) for spacecraft is essential for ensuring safe and reliable conditions for deep space human exploration. Electrical protection and control technologies on the National Aeronautics and Space Administration’s (NASA’s) current human space platform relies heavily on ground support to monitor and diagnose power systems and failures. As communication bandwidth diminishes for deep space applications, a transformation in system monitoring and control becomes necessary to maintain high reliability of electric power service. This paper presents a novel approach for on-line power system security monitoring of autonomous deep space spacecraft.

As the increased distance between Earth-based mission control and the spacecraft results in increasing communication delays, small crews cannot take on all functions performed by ground today, and so vehicles must be more automated to reduce the crew workload for such missions. In addition, both near-term and future missions will feature significant periods when crew is not present, meaning the vehicles will need to operate themselves autonomously. NASA's Advanced Exploration Systems Program pioneers new approaches for rapidly developing prototype systems, demonstrating key capabilities, and validating operational concepts for future human missions beyond low-Earth orbit. Under this program, NASA has developed and demonstrated multiple technologies to enable the autonomous operation of a dormant space habitat. These technologies included a fault-tolerant avionics architecture, novel spacecraft power system and power system controller, and autonomy software to control the habitat. The demonstration involved simulation of the habitat and multiple spacecraft sub-systems (power storage and distribution, avionics, and air-side life-support) during a multi-day test at NASA's Johnson Space Center. The foundation of the demonstration was ‘quiescent operations' of a habitat during a 55 minute eclipse period. For this demonstration, the spacecraft power distribution system and air-side life support system were simulated at a high level of fidelity; additional systems were managed, but with lower fidelity operational constraints and system behavior. Operational constraints for real and simulated loads were developed by analyzing on-orbit hardware and evaluating future Exploration capable technology. A total of 13 real and simulated loads were used during the test. Eight scenarios including both nominal and off-nominal conditions were performed. Over the course of the test, every application performed its desired functions successfully during the simulated tests. The results will inform both future tests, as well as provide insight to NASA's domestic and international partners, as they construct the next generation of space habitats to be used on beyond-Earth missions.

Autonomous control of a spacecraft is an enabling technology that must be developed for deep space human exploration. NASA's current long term human space platform, the International Space Station which is in Low Earth Orbit, is in almost continuous communication with ground based mission control. This allows near real-time control of all the vehicle core systems, including power, to be controlled by the ground. As the focus shifts from Low Earth Orbit, communication time-lag and bandwidth limitations beyond geosynchronous orbit does not permit this type of ground based operation. This paper presents the ongoing work at NASA to develop an architecture for autonomous power control system and a vehicle manager which monitors, coordinates, and delegates all the onboard subsystems to enable autonomous control of the complete spacecraft.

The aeronautics industry has been challenged to increase efficiency, reduce noise and emissions, and decrease dependency on carbon-based fuels. To address these needs, NASA has identified and begun to pursue electrified aircraft as a possible solution. The power system for an electric aircraft can exist in many different forms, however; at the early design stage the engineer(s) must identify whether a hybrid- or turbo- electric solution may be best, whether the power transmission system is to be AC or DC, and to ultimately answer the question: does the electric solution provide a net system benefit compared to the fully mechanical solution? This paper describes a generalized power system architecture sizing and analysis framework to provide a mechanism to answering these questions, along with an example based on the STARC-ABL Architecture.

Aggressive design goals have been set for future aero-propulsion systems with regards to fuel economy, noise, and emissions. To meet these challenging goals, advanced propulsion concepts are being explored and current operating margins are being re-evaluated to find additional concessions that can be made. One advanced propulsion concept being evaluated is a geared turbofan with a variable area fan nozzle (VAFN), developed by NASA. This engine features a small core, a fan driven by the low pressure turbine through a reduction gearbox, and a shape memory alloy (SMA) actuated VAFN. The VAFN is designed to allow both a small exit area for efficient operation at cruise, while being able to open wider at high power conditions to reduce backpressure on the fan and ensure a safe level of stall margin is maintained. The VAFN is actuated via a SMA-based system instead of a conventional system to decrease overall weight of the system, however, SMA-based actuators respond relatively slowly, which introduces dynamic issues that are investigated in this work. This paper describes both a control system designed specifically for issues associated with SMAs, and dynamic analysis of the geared turbofan VAFN with the SMA actuators. Also, some future recommendations are provided for this type of propulsion system.

The Convergent Aeronautics Solutions (CAS) High Voltage-Hybrid Electric Propulsion (HVHEP) task was formulated to support the move into future hybrid-electric aircraft. The goal of this project is to develop a new AC power architecture to support the needs of higher efficiency and lower emissions. This proposed architecture will adopt the use of the doublyfed induction machine (DFIM) for propulsor drive motor application. DFIMs are attractive for several reasons, including but not limited to the ability to self-start, ability to operate suband super-synchronously, and requiring power converters rated at a fraction of what would be required in a corresponding DC system, depending on the required range of operation. The focus of this paper is based specifically on the presentation and analysis of a novel strategy which allows for independent operation of each of the aforementioned doubly-fed induction motors. This strategy includes synchronization, soft-start, and closed loop speed control of each motor as a means of controlling output thrust; be it concurrently or differentially. The demonstration of this strategy has recently been proven out on a low power test bed using fractional horsepower machines. Simulation and hardware test results are presented in the paper.