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NASA NTRS2018

Development and Use of the SPACE Computer Code for Analyzing the Space Station Electrical Power System

This special publication tells the story of the dedicated efforts of very talented individuals to create a preeminent space electrical power system modeling and simulation tool called SPACE, short for System Power Analysis for Capability Evaluation. This computer model has evolved for 30 years, withstanding the test of time and obsolescence, and garnering international recognition for its ability to simulate complex space electrical power systems. The analytical results from this model have saved millions of dollars in hardware redesign, testing, and verification for NASA's International Space Station (ISS) and its European and Russian partners. SPACE has played a pivotal role in the station's design and development and continues to support its ongoing operation. It has also extended its reach beyond the ISS to other key NASA programs, where it guides the design and planned operation of NASA's Multi-Purpose Crew Vehicle Orion and simulates electric power system operation in a dusty atmosphere on Mars' surface. The SPACE lineage was created by a core civil servant staff, supplemented by a cadre of interns and other temporary helpers. They created a tightly integrated tool that includes all phenomena that impact a solar array and battery space power system performance. SPACE is self-contained, requiring no other software modules and associated license fees. SPACE "rings true" in that is has been extensively validated with ISS on-orbit telemetry data. This report is being released as the generation of engineers who created it are nearing retirement, passing the baton to a new generation. This next generation will carry the code into the future, no doubt further evolving it to be able to assure mission planners that newly conceived systems will successfully power NASA's next endeavors. As a previous SPACE code developer and analyst, I have worked alongside many of the people mentioned in this report. The engineers who created the code, along with those just now learning it, are among the best and brightest at NASA. It is an honor to write this foreword as the present Branch Chief under which the legacy of SPACE continues to thrive.

Electrical Power System↗

NASA NTRS2016

Constraining the Size of Near Earth Asteroids

Quick and accurate determination of the size of an asteroid is of great interest to the Asteroid Threat Assessment Project and is difficult to accomplish. With a combination of visible and thermal measurements we employ a method that leverages the size estimations of each model as physical constraints on the true diameter. This method breaks degeneracies present in the thermal and visible model from sparse data. In the visible bands we use both the established H-G relationship and its successor the H-G1G2 model, which has improved capabilities in the opposition effect and large phase angles. For the thermal models we use the Near Earth Asteroid Thermal Model (NEATM), the Night Emission Simulated Thermal Model (NESTM), and the Advanced Thermophysical Model (ATPM).

Nelson, Tyler↗

NASA NTRS2015

Effects of Resolution and Spectral Nudging in Simulation the Effects of Wintertime Atmospheric River Landfalls in the Western US

Landfalling atmospheric rivers (ARs) play a crucial role in the climate of the US Pacific coast region as they are frequently related with heavy precipitation and flash flooding events. Thus, the capability of climate models to accurately simulate AR landfalls and their key hydrologic effects is an important practical concern for WUS, from flood forecasting to future water resources projections. In order to examine the effects of model configuration, including the resolution and spectral nudging, in simulating the climatology of key weather events in the conterminous US, a NASA team has performed a hindcast experiment using the GEOS5 global and the NU-WRF regional models for Nov 1999 - Oct 2010. This study examines the skill of these hindcasts, with different models and their configurations, in simulating key footprints of landfalling ARs in the WUS region. Using an AR-landfall chronology based on the vertically-integrated water vapor flux calculated from the MERRA2 reanalysis, we have analyzed the observed and simulated precipitation and temperature anomalies associated with wintertime AR landfalls along the US Pacific coast. Model skill is measured using metrics including regional means, a skill score based on correlations and mean-square errors, and Taylor diagrams in four WUS Bukovsky regions. Results show that the AR-related anomalies of precipitation is more reliable than of surface temperatures. Model skill also varies according to regions. The AR temperature anomalies are well simulated in most of the WUS region except PNW. For precipitation, simulations with finer spatial resolution tend to generate larger spatial variability and agree better with the PRISM data in most regions. Such a resolution dependence of spatial variability is not found for temperatures; e.g., the MERRA2 reanalysis often outperforms, with similar spatial variability and higher pattern correlations with the PRISM data, finer-resolution NU-WRF runs in simulating temperature variations within subregions. Results from this study will be summarized to assist future (regional) climate experiments for climate change impact assessments and developing adaptationmitigation strategies, the key elements of the National Climate Assessment.

Simulation↗

NASA NTRS2018

Data Mining for Vortices on the Earth's Magnetosphere - Algorithm Application for Detection and Analysis

Unsteady processes in the solar wind– magnetosphere interaction, such as vortices developed at the magnetopause boundary by the Kelvin–Helmholtz instability, may contribute to the process of mass, momentum and energy transfer into the Earth’s magnetosphere. The research described in this paper validates an algorithm to automatically detect and characterize vortices based on velocity data from simulations. The vortex identification algorithm (VIA) systematically searches the 3-D velocity fields to identify critical points where the magnitude of the velocity vector vanishes. The velocity gradient tensor is computed and its invariants are used to assess vortex structure in the flow field. We use the Community Coordinated Modeling Center (CCMC) Runs on Request capability to create a series of model runs initialized from the conditions observed by the Cluster mission in the Hwang et al. (2011) analysis of Kelvin–Helmholtz vortices observed during southward interplanetary magnetic field (IMF) conditions. We analyze further the properties of the vortices found in the runs, including the velocity changes within their motion across the magnetosheath. We also demonstrate the potential of our tool to identify and characterize other transient features (e.g., flux transfer events, FTEs) with vortical internal structures. We find that the vortices are associated with flows on the magnetosheath side of the magnetopause that reach speeds greater than the solar wind speed at the bow shock.

Collado-Vega, Yaireska M.↗

NASA NTRS2019

Bit Error Rate and Frame Error Rate Data Processing for Space Communications and Navigation-Related Communication System Analysis Tools

One of the capabilities that the Space Communications and Navigation (SCaN) Strategic Center for Networking, Integration, and Communications (SCENIC) user interface (UI) web application intends to provide its users is the addition of network protocol and link encryption augmentations of communication system analyses. Before any of these analyses capabilities can be modeled, the simulations of bit error rate (BER) and frame error rate (FER) against signal-to-noise ratio (SNR) have been conducted, requiring parameters from several known coding types (low-density parity-check (LDPC), convolutional, etc.), signal modulations (binary phase shift keying (BPSK), quadrature phase shift keying (QPSK), etc.), coding rates (1/2, 1/3, etc.), and frame sizes (1,280, 3,580, etc.). However, in order to extract useful information from the results of these simulations, a curve fitting technique has been applied to each resulting dataset to extend and extrapolate the curve fit of BER and FER down to 10–30 using MATLAB® Curve Fitting Toolbox™ (The MathWorks, Inc.). This is a necessary step because simulations of BER and FER were only performed to around 10–9 due to the extensive simulation time that would be required to obtain significant simulation results at the error levels desired. Furthermore, the fitted curve results were applied to a finer resolution for the SNR at 0.01-dB interval instead of the 0.05-dB interval limitation used in the simulation. All the possible combinations of the coding types, signal modulations, coding rates, frame sizes, and the extension of BER and FER curves would enable users to capture a wide range of link performances that directly relates to the addition of higher level networking data encapsulated in a frame. The curve fitting results also led to the modeling of the optical link error rate performance by solving for coding gain, FER_BER SNR delta, coded optical BER-SNR, and coded optical FER–SNR.

Communication link analysis↗

NASA NTRS2019

Heatshield for Extreme Entry Environment Technology (HEEET) Thermal Protection System (TPS)

Over the last 5 years, the Heatshield for Extreme Entry Environment Technology (HEEET) project has been working to mature a 3-D Woven Thermal Protection System (TPS) to Technical Readiness Level (TRL) 6 to support future NASA missions to destinations with extreme entry environments such as Venus, Saturn, Uranus, Neptune and high speed sample return missions to Earth. A key aspect of the project has been the building and testing of a 1-meter base diameter Engineering Test Unit (ETU) representative of what could be used for a Saturn probe. This paper provides a high level overview of the HEEET project including manufacturing and testing of the ETU which has been subjected to mission relevant thermal and mechanical loads, to verify structural models, establish system capability and verify manufacturing workmanship.

TPS↗

NASA NTRS2019

LTF/Fluid and Cryogenic Systems Branch

Functions of the Branch: Cross-Cutting Fluids Engineering; Research and Technology Development of Cryogenic Fluid Management (CFM) Systems; Component and System level; Design, Development Test and Evaluation (DDT&E) for Fluid, CFM, Propellant and Gaseous Systems; Fluid Component Specification and Selection; Code Compliance of Pressurized Systems; Fluid/Cryogenic System Performance Analysis and Trade Studies; Hazards Analysis and Risk Assessment of Fluidic Systems; Fluids Modeling and Simulation Capabilities

Fluid↗

NASA NTRS2019

Boundary Layer Stability and Transition in a Chemically Reacting Martian Atmosphere Using LASTRAC

The Thermal Protection System (TPS) is a significant portion of the mass of reentry vehicles, planetary probes, and Martian entry vehicles. Reducing this mass has benefits in terms of decreased fuel requirements and increased payload; however, due to the high risk and uncertainty, the TPS or heat shields are designed conservatively by assuming fully turbulent flow. Laminar flow results in reduced heat flux, and improved transition prediction has the potential to reduce TPS mass and uncertainty in aerothermodynamic predictions. Limited previous research exists examining the problem of transition prediction for Martian atmospheric entry, with studies available on transition on the Mars Science Laboratory TPS. Although transition was demonstrated in wind-tunnel tests, uncertainty in the transition location resulted in a TPS designed for fully turbulent flow, and therefore greater mass than required for a partially laminar condition. In this work, we extend the boundary layer stability code LASTRAC, recently modified to include chemical and thermal nonequilibrium capabilities, to a model of the Martian atmosphere. LASTRAC provides Parabolized Stability Equations (PSE) as well as Linear Stability Theory (LST) to predict the stability of a boundary layer and transition with semi-empirical e(sup N) methods. Results included in this work compare disturbance growth characteristics between air and Martian atmosphere at similar non-dimensional freestream conditions on a simple flat plate geometry. Both chemical nonequilibrium and thermochemical nonequilibrium, as well as both PSE and LST, are used.

Kline, H. L.↗

NASA NTRS2020

eVTOL Passenger Acceptance

With the expected introduction of electric vertical takeoff and landing (eVTOL) aircraft for urban air mobility (UAM) services, passenger acceptance has become an issue of interest to manufacturers and operators. This study took an initial look at what passengers expect from an eVTOL UAM flight experience – what aspects matter most, what might be acceptable, and where there are gaps in our understanding. The analysis included a literature search and interviews with experts from the aviation community to identify passenger concerns and potential mitigations. Passenger concerns were found to fall into six general categories: perceived safety, noise and vibration, availability and access, passenger well-being, concern for the environment, and vehicle motion. The study used a modified quality function deployment approach to correlate these passenger concerns with design and operational variables, highlighting how design and operational parameters can mitigate the passenger concerns. NASA research can address the passenger concerns by developing simulation capabilities and noise models, characterizing propulsion system performance, taking direct measurem and conducting further studies of market demand and design methods.

Edwards, Thomas↗

NASA NTRSDate not supplied

Mitigation of Nacelle/Pylon Wake on the High-Lift Common Research Model Using a Nacelle Chine

A 10% scale, high-lift version of the Common Research Model (CRM-HL) was tested in the NASA Langley Research Center 14-by22-Foot Subsonic Tunnel. The focus of the wind tunnel test campaign was to assess the feasibility of active flow control (AFC) on the simplified CRM-HL configuration. The modular design of the CRM-HL model enabled the testing of the conventional CRM-HL version to establish a benchmark for the AFC research. The wind tunnel model has the capability of being tested with and without the engine nacelle/pylon for comparison. The wind tunnel investigation included the acquisition of force and moment data, steady pressure data, as well as surface flow visualization using minitufts. For some select cases, numerical simulations were performed to aid in understanding the wind tunnel data. Wind tunnel measurements indicated a lift degradation of the conventional CRM-HL at high angles of attack. The surface flow visualization with fluorescent minitufts revealed that the lift degradation is due to flow separation caused by the nacelle/pylon wake on the inboard wing. The wake and the consequent flow separation were successfully mitigated using a nacelle chine installed on the inboard side of the engine nacelle.

Mehti Koklu↗

NASA NTRSDate not supplied

Boundary Layer Stability and Transition in a Chemically Reacting Martian Atmosphere using LASTRAC

The Thermal Protection System (TPS) is a significant portion of the mass of reentry vehicles, planetary probes, and Martian entry vehicles. Reducing this mass has benefits in terms of decreased fuel requirements and increased payload; however, due to the high risk and un-certainty, the TPS or heat shields are designed conservatively by assuming fully turbulent flow. Laminar flow results in reduced heat flux, and improved transition prediction has the potential to reduce TPS mass and uncertainty in aerothermodynamic predictions. Limited previous research exists examining the problem of transition prediction for Martian atmospheric entry, with studies available on transition on the Mars Science Laboratory TPS. Although transition was demonstrated in wind-tunnel tests, uncertainty in the transition location resulted in a TPS designed for fully turbulent flow, and therefore greater mass than required for a partially-laminar condition. In this work, we extend the boundary layer stability code LASTRAC, recently modified to include chemical and thermal nonequilibrium capabilities, to a model of the Martian atmosphere. LASTRAC provides Parabolized Stability Equations (PSE) as well as Linear Stability Theory (LST) to predict the stability of a boundary layer and transition with semi-empirical eN methods. Results included in this work compare disturbance growth characteristics between air and Martian atmosphere at similar nondimensional freestream conditions on a simple flat plate geometry. Both chemical nonequilibrium and thermochemical nonequilibrium, as well as both PSE and LST, are used.

Heather L Kline↗

NASA NTRS1993

Accuracies of Atmospheric Profiles Obtained from GPS Occultations

Radio occultation studies of the terrestrial atmosphere are possible through use of signals transmitted by satellites of the Global Positioning System (GPS) and received by one or more other satellites in low earth orbit (LEO). The perturbed phase of the occulted signal gives direct information on the refractivity profile in the region of occultation, from which vertical profiles of density, pressure, and temperature can be retrieved. Based on model simulations the capability of GPS to provide atmospheric profiles is assessed.

atmospheric↗

NASA NTRSDate not supplied

Investigation and Evaluation of Advanced Spectrum Management Concepts for Aeronautical Communications

With the emergence of new aerial vehicles into the airspace and the continued growth of aviation operations, there will be an increasing demand for voice and data communications within the National Airspace System (NAS). The continued use of existing VHF and UHF frequency allocations is not a sustainable approach, and as a result, a new spectrum management solution is required to support future mission needs. The proposed spectrum management concepts leverage modern advancements such as artificial intelligence (AI) and big data to dynamically optimize the spectrum utilization based on the predicted communications demand throughout the airspace. This technical investigation considers both air-ground and air-air communications networks, and can be applied to both existing applications such as the air traffic control (ATC) system, as well as future applications, such as the emerging Advanced Air Mobility (AAM). To support the evaluation of the proposed concepts and technologies, a modeling and simulation capability is currently under development and will continue to evolve to support new and advanced airspace applications. It is anticipated that this proposed spectrum concept will better serve the spectrum needs of future NAS applications.

Eric J Knoblock↗

NASA NTRSDate not supplied

Investigation and Evaluation of Advanced Spectrum Management Concepts for Aeronautical Communications

Eric J Knoblock↗

NASA NTRSDate not supplied

Aeroacoustic Characterization of Optimum Hovering Rotors using Artificial Neural Networks

This work illustrates the use of artificial neural network modeling in the aerodynamic and aeroacoustic characterization of optimum hovering rotors over a broad range of design and operating conditions. Design of Experiments was used to create input feature spaces over eight input factors: the number of rotor blades, rotor radius, rotor rotation rate, design thrust condition, collective pitch, airfoil camber, the location of maximum camber, and the airfoil thickness. A low-fidelity tool chain was then used at the discrete data points defined by the designed input feature spaces to analytically design optimum hovering rotors and simulate aerodynamic and aeroacoustic quantities. This allowed for the generation of data sets over which to train and test the artificial neural network prediction models. Prediction models were trained over the data sets for the actual thrust generated by the rotor, power loading, tonal thickness and loading noise at the fundamental blade passage frequency, and broadband self-noise at seventeen one-third octave bands between 1 kHz and 40 kHz. These prediction models were validated by testing over data previously unseen by the models to quantify their capability for generalization to new data within the design feature space. The models were then used to study the effect each input feature had on the aeroacoustics and aerodynamics of optimum hovering rotors and physical insights were concluded to further explain the effect of each input. This characterization study showed that tonal noise and power loading were most sensitive to the number of rotor blades and the rotor rotation rate and that broadband noise was most sensitive to collective pitch and the design thrust condition.

Christopher S Thurman↗

NASA NTRSDate not supplied

Evaluation of VSPAERO Analysis Capabilities for Conceptual Design of Aircraft with Propeller-Blown Wings

Advancements in electric propulsion and the emergence of Advanced Air Mobility are driving the evolution of new aircraft designs. Since electric propulsion enables flexibility in propeller location, there is an increasing need for reliable, quick analyses of propeller-airframe interactions during the conceptual design phase. Many existing analysis tools capable of accurately modeling propeller-airframe interactions are computationally expensive and require a high level of expertise and significant time investment for setup. VSPAERO is a NASA-developed, open source, computational analysis tool that runs a Vortex-Lattice Method (VLM) solver and is targeted at conceptual design. This paper assesses the applicability of the VSPAERO VLM in the conceptual design phase by comparing VSPAERO predictions to predictions by OVERFLOW, a Reynolds-Averaged Navier-Stokes Computational Fluid Dynamics solver, and RoBIN, another VLM tool. The paper details the modeling, meshing, and analysis techniques used within VSPAERO. Analyses were performed for a wing in isolation, a propeller in isolation, and then for two propeller-blown wing configurations: one with a propeller located at the midspan and another with a propeller located at the wingtip. The propeller was modeled both as an actuator disk and as rotating blades.

VSPAERO↗

NASA NTRS2021

A New Method for Predicting Turbulent Flow Reattachment Location: Application of Stratford Criterion for Reattaching Flows

A new method for predicting turbulent flow reattachment location has been developed. The method predicts the reattachment location using the surface static pressure distribution and requires only a single empirical parameter. The method is based on the well-known Stratford’s flow separation criterion, which results from an approximate solution to the equations of motion within the boundary layer. Because of the large pressure rise, the original Stratford separation criterion is not valid for reattaching flows. In order to apply the Stratford criterion for reattaching flows, the reference location was moved to the pressure drop conditions instead of pressure rise conditions. In addition, the pressure distribution was scaled using a technique that was originally introduced for supersonic base flows. A new empirical parameter was also obtained for the modified Stratford criterion. The method has been tested for 30 different separated flow configurations from the literature. The variety of test cases include subsonic flows, transonic flows, 2D flows, and axisymmetric flows, with experimental as well as high resolution numerical simulation results. The flow reattachment predictions with the new method agree very well with the reported data. The error is less than 5% and typically about 2%. The new method is an extremely simple and a quick way of finding the reattachment location. Given the complexities of the existing experimental techniques for finding the reattachment location, the method easily and quickly provides the flow reattachment location, which could be used to estimate the physical extent of separation bubbles, as a performance index for flow control methods, or to assess the predictive capability of turbulence models.

Flow reattachment location↗

NASA NTRSDate not supplied

Investigation of Intelligent Resource Management for Aviation Communications

The emergence of new aerial vehicles into the airspace as part of new initiatives, such as Advanced Air Mobility (AAM), will place growing demand for spectrum resources to support airspace operations. The traditional approach of using fixed channel allocations within standard service volumes will not allow for dynamic and efficient distribution of resources based on airspace demand; consequently, a new approach to aviation spectrum management will be required to meet the anticipated needs of airspace users. The National Aeronautics and Space Administration (NASA) is investigating the application of advanced concepts to implement a novel spectrum management approach that allows for the intelligent utilization of aviation spectrum throughout the airspace while maintaining the quality of service prescribed by aeronautical standards. This technical investigation evaluates the dynamic assignment of resources for both air-ground and air-air communication links applicable to both the emerging AAM initiative as well as the existing air traffic management system. The performance of the proposed spectrum management concepts will be evaluated using a custom modeling and simulation capability that is currently under development. The implementation of these approaches is anticipated to facilitate increased spectrum utilization efficiency and enhanced airspace capacity, which will better serve the needs of future applications.

Aeronautics↗