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An evaluation of simplifications for the thruster power processor interface for a 30 cm Hg ion thruster is presented. Tests on the engine, thruster control, and the power supplies are performed. Reduced power processors requirements are defined and the impact on thruster design, performance, and lifetime are assessed.
A conceptual vehicle design enabling fast outer solar system travel was produced predicated on a small aspect ratio spherical torus nuclear fusion reactor. Initial requirements were for a human mission to Saturn with a greater than 5% payload mass fraction and a one way trip time of less than one year. Analysis revealed that the vehicle could deliver a 108 mt crew habitat payload to Saturn rendezvous in 235 days, with an initial mass in low Earth orbit of 2,941 mt. Engineering conceptual design, analysis, and assessment was performed on all ma or systems including payload, central truss, nuclear reactor (including divertor and fuel injector), power conversion (including turbine, compressor, alternator, radiator, recuperator, and conditioning), magnetic nozzle, neutral beam injector, tankage, start/re-start reactor and battery, refrigeration, communications, reaction control, and in-space operations. Detailed assessment was done on reactor operations, including plasma characteristics, power balance, power utilization, and component design.
The proposed framework derives a set of quality metrics to provide critical insights into and tracking of grid operations, sensor performance, sensor longevity, and event statistics. Power grid engineers can utilize this information to identify problems with existing sensor locations and problematic power grid assets including generators, transmission lines, load centers, and substations. This information can also be used to identify unexpected/abnormal behavior of power grid components, improve power grid observability, and operational monitoring, and thus enhance real-time decision-making support system. Power grid planners can utilize this information to augment existing sensing architecture with new sensors and improve the observability of the network.
The J2X Gas Generator engine design specifications include dynamic, spontaneous, and broadband combustion stability requirements. These requirements are verified empirically based high frequency chamber pressure measurements and analyses. Dynamic stability is determined with the dynamic pressure response due to an artificial perturbation of the combustion chamber pressure (bomb testing), and spontaneous and broadband stability are determined from the dynamic pressure responses during steady operation starting at specified power levels. J2X Workhorse Gas Generator testing included bomb tests with multiple hardware configurations and operating conditions, including a configuration used explicitly for engine verification test series. This work covers signal processing techniques developed at Marshall Space Flight Center (MSFC) to help assess engine design stability requirements. Dynamic stability assessments were performed following both the CPIA 655 guidelines and a MSFC in-house developed statistical-based approach. The statistical approach was developed to better verify when the dynamic pressure amplitudes corresponding to a particular frequency returned back to pre-bomb characteristics. This was accomplished by first determining the statistical characteristics of the pre-bomb dynamic levels. The pre-bomb statistical characterization provided 95% coverage bounds; these bounds were used as a quantitative measure to determine when the post-bomb signal returned to pre-bomb conditions. The time for post-bomb levels to acceptably return to pre-bomb levels was compared to the dominant frequency-dependent time recommended by CPIA 655. Results for multiple test configurations, including stable and unstable configurations, were reviewed. Spontaneous stability was assessed using two processes: 1) characterization of the ratio of the peak response amplitudes to the excited chamber acoustic mode amplitudes and 2) characterization of the variability of the peak response's frequency over the test duration. This characterization process assists in evaluating the discreteness of a signal as well as the stability of the chamber response. Broadband stability was assessed using a running root-mean-square evaluation. These techniques were also employed, in a comparative analysis, on available Fastrac data, and these results are presented here.
Inertial fusion can be used to power spacecraft within the solar system and beyond. Such spacecraft have the potential for short-duration manned-mission performance exceeding other technologies. We are conducting a study to assess the systems aspects of inertial fusion as applied to such missions, based on the conceptual engine design of Hyde (1983) we describe the required systems for an entirely new spacecraft design called VISTA that is based on the use of DT fuel. We give preliminary design details for the power conversion and power conditioning systems for manned missions to Mars of total duration of about 100 days. Specific mission performance results will be published elsewhere, after the study has been completed.
It was previously observed that an incident acoustic field on a wing with laminar flow can cause transition to turbulent flow if the fluctuating acoustic velocities are of sufficient amplitude and in the critical frequency range for an unstable laminar boundary layer. A section of a wing was modified with a natural laminar flow (NLF) glove to allow direct measurement of the effect of varying engine noise on the extent of laminar flow. The flight test program was completed in June, 1985. At each flight condition, the engine power was varied from about 2600 r/min (idle) to about 4500 r/min (maximum continuous power). The spectral data provides considerable insight into the influences of the various sound sources that contribute to the overall noise levels. Additional analysis will be required to assess the impact of these sources on boundary layer transition. These results demonstrate that substantial laminar flow on the wing of a transport configuration with wing-mounted engines can be obtained.
One of the most demanding tasks that must be performed by the Space Shuttle flight crew is the process of determining whether, when and where to abort the vehicle should engine or system failures occur during ascent or entry. Current Shuttle abort procedures involve paging through complicated paper checklists to decide on the type of abort and where to abort. Additional checklists then lead the crew through a series of actions to execute the desired abort. This process is even more difficult and time consuming in the absence of ground communications since the ground flight controllers have the analysis tools and information that is currently not available in the Shuttle cockpit. Crew workload specifically abort procedures will be greatly simplified with the implementation of the Space Shuttle Cockpit Avionics Upgrade (CAU) project. The intent of CAU is to maximize crew situational awareness and reduce flight workload thru enhanced controls and displays, and onboard abort assessment and determination capability. SAFM was developed to help satisfy the CAU objectives by providing the crew with dynamic information about the capability of the vehicle to perform a variety of abort options during ascent and entry. This paper- presents an overview of the SAFM application. As shown in Figure 1, SAFM processes the vehicle navigation state and other guidance information to provide the CAU displays with evaluations of abort options, as well as landing site recommendations. This is accomplished by three main SAFM components: the Sequencer Executive, the Powered Flight Function, and the Glided Flight Function, The Sequencer Executive dispatches the Powered and Glided Flight Functions to evaluate the vehicle's capability to execute the current mission (or current abort), as well as more than IS hypothetical abort options or scenarios. Scenarios are sequenced and evaluated throughout powered and glided flight. Abort scenarios evaluated include Abort to Orbit (ATO), Transatlantic Abort Landing (TAL), East Coast Abort Landing (ECAL) and Return to Launch Site (RTLS). Sequential and simultaneous engine failures are assessed and landing footprint information is provided during actual entry scenarios as well as hypothetical "loss of thrust now" scenarios during ascent.
Digital fault-tolerant computer-based systems have become commonplace in military and commercial avionics. These systems hold the promise of increased availability, reliability, and maintainability over conventional analog-based systems through the application of replicated digital computers arranged in fault-tolerant configurations. Three tightly coupled factors of paramount importance, ultimately determining the viability of these systems, are reliability, safety, and profitability. Reliability, the major driver affects virtually every aspect of design, packaging, and field operations, and eventually produces profit for commercial applications or increased national security. However, the utilization of digital computer systems makes the task of producing credible reliability assessment a formidable one for the reliability engineer. The root of the problem lies in the digital computer's unique adaptability to changing requirements, computational power, and ability to test itself efficiently. Addressed here are the nuances of modeling the reliability of systems with large state sizes, in the Markov sense, which result from systems based on replicated redundant hardware and to discuss the modeling of factors which can reduce reliability without concomitant depletion of hardware. Advanced fault-handling models are described and methods of acquiring and measuring parameters for these models are delineated.
The fatigue damage of a space propulsion system component is computed using probabilistic structural analysis methods. The analysis takes into account the variations in static and dynamic loads, the uncertainty in structural damping, and the scatter in material fatigue resistance. The key elements of the probabilistic approach include: (1) a numerical engine model for describing the global component interface loads consistent with engine balance, (2) models for computing the local mode boundary conditions on the component, (3) a static structural analysis model that captures the strains at a damage critical location as a function of engine performance variables, (4) a finite element model for assessment of the random amplitude stress response due to random base and pressure excitations with uncertain power and correlation length, and (5) advanced first order reliability methods for computing the probabilities associated with the fatigue damage.
The status of the NEXT 2000 hour wear test is presented. This test is being conducted with a 40 cm engineering model ion engine, designated EM1, at a beam current higher than listed on the NEXT throttle table. Pretest performance assessments demonstrated that EM1 satisfies all thruster performance requirements. As of 7/3/03, the ion engine has accumulated 406 hours of operation at a thruster input power of 6.9 kW. Overall ion engine performance, which includes thrust, thruster input power, specific impulse, and thrust efficiency, has been steady to date with no indications of performance degradation. Images of the downstream discharge cathode, neutralizer, and accelerator aperture surfaces have exhibited no significant erosion to date.
In order to realize the vision of expanding human presence in space, NASA will develop new technologies that can enable future crewed spacecraft to go far beyond Earth orbit. These technologies must be matured to the point that future project managers can accept the risk of incorporating them safely and effectively within integrated spacecraft systems, to satisfy very challenging mission requirements. The technologies must also be applied and managed within an operational context that includes both on-board crew and mission support on Earth. The Advanced Exploration Systems (AES) Program is one part of the NASA strategy to identify and develop key capabilities for human spaceflight, and mature them for future use. To support this initiative, the Integrated Power Avionics and Software (iPAS) environment has been developed that allows engineers, crew, and flight operators to mature promising technologies into applicable capabilities, and to assess the value of these capabilities within a space mission context. This paper describes the development of the integration environment to support technology maturation and risk reduction, and offers examples of technology and mission demonstrations executed to date.
NASA has a consistent need for radioisotope power systems (RPS) to enable robotic scientific missions for planetary exploration that has been present for over four decades and will continue into the foreseeable future, as documented in the most recent Planetary Science Decadal Study Report. As RPS have evolved throughout the years, there has also grown a desire for more efficient power systems, allowing NASA to serve as good stewards of the limited plutonium-238 (238Pu), while also supporting the ever-present need to minimize mass and potential impacts to the desired science measurements. In fact, the recent Nuclear Power Assessment Study (NPAS) released in April 2015 resulted in several key conclusion regarding RPS, including affirmation that RPS will be necessary well into the 2030s (at least) and that 238Pu is indeed a precious resource requiring efficient utilization and preservation. Stirling Radioisotope Generators (SRGs) combine a Stirling cycle engine powered by a radioisotope heater unit into a single generator system. Stirling engine technology has been under development at NASA Glenn Research Center (GRC) in partnership with the Department of Energy (DOE) since the 1970's. The most recent design, the 238Pu-fueled Advanced Stirling Radioisotope Generator (ASRG), was offered as part of the NASA Discovery 2010 Announcement of Opportunity (AO). The Step-2 selections for this AO included two ASRG-enabled concepts, the Titan Mare Explorer (TiME) and the Comet Hopper (CHopper), although the only non-nuclear concept, InSight, was ultimately chosen. The DOE's ASRG contract was terminated in 2013. Given that SRGs utilize significantly less 238Pu than traditional Radioisotope Thermoelectric Generators (RTGs) - approximately one quarter of the nuclear fuel, to produce similar electrical power output - they provide a technology worthy of consideration for meeting the aforementioned NASA objectives. NASA's RPS Program Office has recently investigated a new Stirling to Flight (S2F) initiative with the objective of developing a 100-500 We Stirling generator system. Additionally, a different approach is being devised for this initiative to avoid pitfalls of the past, and apply lessons learned from the recent ASRG experience. Two key aspects of this initiative are a Stirling System Technology Maturation Effort, and a Surrogate Mission Team (SMT) intended to provide clear mission pull and requirements context. The S2F project seeks to lead directly into a DOE flight system development of a new SRG. This paper will detail the proposed S2F initiative, and provide specifics on the key efforts designed to pave a forward path for bringing Stirling technology to flight.
The National Aeronautics and Space Administration (NASA) Safety & Mission Assurance (S&MA) directorate at the Johnson Space Center (JSC) has applied its knowledge and experience with Probabilistic Risk Assessment (PRA) to projects in industries ranging from spacecraft to nuclear power plants. PRA is a comprehensive and structured process for analyzing risk in complex engineered systems and/or processes. The PRA process enables the user to identify potential risk contributors such as, hardware and software failure, human error, and external events. Recent developments in the oil and gas industry have presented opportunities for NASA to lend their PRA expertise to both ongoing and developmental projects within the industry. This paper provides an overview of the PRA process and demonstrates how this process was applied in estimating the probability that a Mobile Offshore Drilling Unit (MODU) operating in the Gulf of Mexico and equipped with a generically configured Dynamic Positioning System (DPS) loses location and needs to initiate an emergency disconnect. The PRA described in this paper is intended to be generic such that the vessel meets the general requirements of an International Maritime Organization (IMO) Maritime Safety Committee (MSC)/Circ. 645 Class 3 dynamically positioned vessel. The results of this analysis are not intended to be applied to any specific drilling vessel, although provisions were made to allow the analysis to be configured to a specific vessel if required.
The National Aeronautics and Space Administration (NASA) Safety & Mission Assurance (S&MA) directorate at the Johnson Space Center (JSC) has applied its knowledge and experience with Probabilistic Risk Assessment (PRA) to projects in industries ranging from spacecraft to nuclear power plants. PRA is a comprehensive and structured process for analyzing risk in complex engineered systems and/or processes. The PRA process enables the user to identify potential risk contributors such as, hardware and software failure, human error, and external events. Recent developments in the oil and gas industry have presented opportunities for NASA to lend their PRA expertise to both ongoing and developmental projects within the industry. This paper provides an overview of the PRA process and demonstrates how this process was applied in estimating the probability that a Mobile Offshore Drilling Unit (MODU) operating in the Gulf of Mexico and equipped with a generically configured Dynamic Positioning System (DPS) loses location and needs to initiate an emergency disconnect. The PRA described in this paper is intended to be generic such that the vessel meets the general requirements of an International Maritime Organization (IMO) Maritime Safety Committee (MSC)/Circ. 645 Class 3 dynamically positioned vessel. The results of this analysis are not intended to be applied to any specific drilling vessel, although provisions were made to allow the analysis to be configured to a specific vessel if required.
The NASA Lewis Research Center's experimental and theoretical research shows that wave rotor topping can significantly enhance gas turbine engine performance levels. Engine-specific fuel consumption and specific power are potentially enhanced by 15 and 20 percent, respectively, in small (e.g., 400 to 700 hp) and intermediate (e.g., 3000 to 5000 hp) turboshaft engines. Furthermore, there is potential for a 3- to 6-percent specific fuel consumption enhancement in large (e.g., 80,000 to 100,000 lbf) turbofan engines. This wave-rotor-enhanced engine performance is accomplished within current material-limited temperature constraints. The completed first phase of experimental testing involved a three-port wave rotor cycle in which medium total pressure inlet air was divided into two outlet streams, one of higher total pressure and one of lower total pressure. The experiment successfully provided the data needed to characterize viscous, partial admission, and leakage loss mechanisms. Statistical analysis indicated that wave rotor product efficiency decreases linearly with the rotor to end-wall gap, the square of the friction factor, and the square of the passage of nondimensional opening time. Brush seals were installed to further minimize rotor passage-to-cavity leakage. The graph shows the effect of brush seals on wave rotor product efficiency. For the second-phase experiment, which involves a four-port wave rotor cycle in which heat is added to the Brayton cycle in an external burner, a one-dimensional design/analysis code is used in conjunction with a wave rotor performance optimization scheme and a two-dimensional Navier-Stokes code. The purpose of the four-port experiment is to demonstrate and validate the numerically predicted four-port pressure ratio versus temperature ratio at pressures and temperatures lower than those that would be encountered in a future wave rotor/demonstrator engine test. Lewis and the Allison Engine Company are collaborating to investigate wave rotor integration in an existing turboshaft engine. Recent theoretical efforts include simulating wave rotor dynamics (e.g., startup and load-change transient analysis), modifying the one-dimensional wave rotor code to simulate combustion internal to the wave rotor, and developing an analytical wave rotor design/analysis tool based on macroscopic balances for parametric wave rotor/engine analysis.
This slide presentation reviews the importance of Risk Informed Design (RID) as an important feature of the systems engineering process. RID is based on the principle that risk is a design commodity such as mass, volume, cost or power. It also reviews Probabilistic Risk Assessment (PRA) as it is used in the product life cycle in the development of NASA's Constellation Program.
Island communities often struggle to establish and maintain traditional electric grids and are therefore heavily reliant on costly imported fossil fuels. In the case of Puerto Rico, these challenges are enhanced by extreme weather and other natural hazards that threaten the local electricity generation and transmission infrastructure. Ocean thermal energy conversion (OTEC) could play an important role in establishing a more resilient electrical grid in the region. Here, in this study, a detailed analysis is conducted to characterize the ocean thermal resource and power potential of OTEC in Puerto Rico based on a 14-year dataset of modeled ocean temperature. The assessment considers seasonal and interannual variability in the region's thermal resource and examines the operational limitations associated with minimal thermal gradients required to run a typical OTEC heat engine. Notably, the local thermal resource is found to be sensitive to El Niño-Southern Oscillation (ENSO) climate patterns, with La Niña conditions linked to greater OTEC power availability. Seven areas of opportunity are identified based on their resource potential and proximity to existing electrical distribution lines, including two that could benefit the nearby U.S. Virgin Islands. The greatest OTEC power potential is observed to the south of the main island of Puerto Rico in the Caribbean Sea with an estimated capacity of 138 MW for a plant pumping cold water from a depth of 1,000 m, or the equivalent amount of electricity required to power 219,000 households.
The Neptune System Explorer (NSE) mission concept study assessed opportunities to conduct Cassini-like science at Neptune with a radioisotope electric propulsion (REP) based spacecraft. REP is based on powering an electric propulsion (EP) engine with a radioisotope power source (RPS). The NSE study was commissioned under the Joint Radioisotope Electric Propulsion Studies (JREPS) project, which sought to determine the technical feasibility of flagship class REP applications. Within JREPS, special emphasis was given toward identifying tall technology tent poles, as well as recommending any new RPS technology developments that would be required for complicated REP missions. Based on the goals of JREPS, multiple RPS (e.g. thermoelectric and Stirling based RPS) and EP (e.g. Hall and ion engines) technology combinations were traded during the NSE study to determine the most favorable REP design architecture. Among the findings from the study was the need for >400We RPS systems, which was driven by EP operating powers and the requirement for a long-lived mission in the deep solar system. Additionally multiple development and implementation risks were identified for the NSE concept, as well as REP missions in general. Among the strengths of the NSE mission would be the benefits associated with RPS and EP use, such as long-term power (approx. 2-3kW) at Neptune and flexible trajectory options for achieving orbit or tours of the Neptune system. Although there are still multiple issues to mitigate, the NSE concept demonstrated distinct advantages associated with using REP for deep space flagship-class missions.