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At least 955 records · Page 53
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Time dependent behavior of a graphite/thermoplastic composite and the effects of stress and physical aging

Two complimentary studies were performed to determine the effects of stress and physical aging on the matrix dominated time dependent properties of IM7/8320 composite. The first of these studies, experimental in nature, used isothermal tensile creep/aging test techniques developed for polymers and adapted them for testing of the composite material. From these tests, the time dependent transverse (S22) and shear (S66) compliance's for an orthotropic plate were found from short term creep compliance measurements at constant, sub-T(sub g) temperatures. These compliance terms were shown to be affected by physical aging. Aging time shift factors and shift rates were found to be a function of temperature and applied stress. The second part of the study relied upon isothermal uniaxial tension tests of IM7/8320 to determine the effects of physical aging on the nonlinear material behavior at elevated temperature. An elastic/viscoplastic constitutive model was used to quantify the effects of aging on the rate-independent plastic and rate-dependent viscoplastic response. Sensitivity of the material constants required by the model to aging time were determined for aging times up to 65 hours. Verification of the analytical model indicated that the effects of prior aging on the nonlinear stress/strain/time data of matrix dominated laminates can be predicted.

Gates, Thomas S.↗
NASA NTRS1992

Code validation for the simulation of supersonic viscous flow about the F-16XL

The viewgraphs and discussion on code validation for the simulation of supersonic viscous flow about the F-16XL are provided. Because of the large potential gains related to laminar flow on the swept wings of supersonic aircraft, interest in the applications of laminar flow control (LFC) techniques in the supersonic regime has increased. A supersonic laminar flow control (SLFC) technology program is currently underway within NASA. The objective of this program is to develop the data base and design methods that are critical to the development of laminar flow control technology for application to supersonic transport aircraft design. Towards this end, the program integrates computational investigations underway at NASA Ames-Moffett and NASA Langley with flight-test investigations being conducted on the F-16XL at the NASA Ames-Dryden Research Facility in cooperation with Rockwell International. The computational goal at NASA Ames-Moffett is to integrate a thin-layer Reynolds averaged Navier-Stokes flow solver with a stability analysis code. The flow solver would provide boundary layer profiles to the stability analysis code which in turn would predict transition on the F-16XL wing. To utilize the stability analysis codes, reliable boundary layer data is necessary at off-design cases. Previously, much of the prediction of boundary layer transition has been accomplished through the coupling of boundary layer codes with stability theory. However, boundary layer codes may have difficulties at high Reynolds numbers, of the order of 100 million, and with the current complex geometry in question. Therefore, a reliable code which solves the thin-layer Reynolds averaged Navier-Stokes equations is needed. Two objectives are discussed, the first in greater depth. The first objective is method verification, via comparisons of computations with experiment, of the reliability and robustness of the code. To successfully implement LFC techniques to the F-16XL wing, the flow about the leading edge must be maintained as laminar flow. Therefore, the second objective is to focus on a series of numerical simulations with different values of angle of attack, alpha, and Reynolds numbers. The purpose of the simulations is to study their effects on the two main factors which precipitate transition to turbulence at leading edges of highly swept wings (e.g., 'spanwise contamination' and 'crossflow instability').

Flores, Jolen↗
NASA NTRS1985

Visualization of Coronary Arteries from Intravenous Angiograms

Under most circumstances, the coronary arteries are not satisfactorily visualized in intravenous angiograms. The objective of this study is to develop computer image enhancement methods that will improve the quality of the latent coronary images to a degree sufficient to detect an obstructive lesion. Such a technique, if successful, could be used as a first step alternative to conventional coronary angiography for individuals with ambiguous noninvasive cardiac tests. The determination of no lesion from the intravenous procedure would relieve the need for the conventional angiogram, while verification of an obstructive lesion could be followed by a conventional angiogram. The nature of the imaging problem and a description of the methods and initial processing results are described in this paper.

Selzer, Robert H.↗
NASA NTRS1994

Results of a Formal Methods Demonstration Project

This paper describes the results of a cooperative study conducted by a team of researchers in formal methods at three NASA Centers to demonstrate FM techniques and to tailor them to critical NASA software systems. This pilot project applied FM to an existing critical software subsystem, the Shuttle's Jet Select subsystem (Phase I of an ongoing study). The present study shows that FM can be used successfully to uncover hidden issues in a highly critical and mature Functional Subsystem Software Requirements (FSSR) specification which are very difficult to discover by traditional means.

formal methods computer system specification compu↗
NASA NTRS2011

Comparison of VIIRS Prelaunch RVS Among Independent Studies

The Visible Infrared Imaging Radiometer Suite (VIIRS) is a key sensor carried on the NPOESS (National Polar-orbiting Operational Environmental Satellite System), upgraded and developed recently from heritage instruments including AVHRR, OLS, MODIS, and SeaWiFS. It has on-board calibration components including a solar diffuser (SD) and a solar diffuser stability monitor (SDSM) for the reflective solar bands (RSB), a V-groove blackbody for the thermal emissive bands (TEB), and a space view (SV) port for background subtraction. These on-board calibrators are located at fixed scan angles. The VIIRS response versus scan angle (RVS) was characterized prelaunch in lab ambient conditions and will be used on-orbit to characterize the response for the all scan angles relative to the calibrator scan angle (SD for RSB and blackbody for TEB). Since the RVS is vitally important to the quality of calibrated radiance products, several independent studies were performed and their results were compared and validated. This document provides RVS results from three groups: the NPP Instrument Calibration Support Team (NICST), Raytheon, and the Aerospace Corporation. A comparison of the RVS results obtained using a 2nd order polynomial fit to measurement data is conducted for each band, detector, and half angle mirror (HAM) side. The associated RVS fitting residuals are examined and compared with the relative differences in RVS found between independent studies. Results show that the agreement is within 0.1% and comparable with fitting residuals for all bands except for RSB band M9, where a difference of 0.2% results from the application of the atmospheric water vapor correction for laboratory conditions during the test by Raytheon. NICST has slightly larger RSB RVS uncertainties but still well within the 0.3% total uncertainty allowed for the RVS characterization defined in the Performance Verification Plan.

Wu, Aisheng↗
NASA NTRS2000

Hierarchical Statistical 3D ' Atomistic' Simulation of Decanano MOSFETs: Drift-Diffusion, Hydrodynamic and Quantum Mechanical Approaches

When MOSFETs are scaled to deep submicron dimensions the discreteness and randomness of the dopant charges in the channel region introduces significant fluctuations in the device characteristics. This effect, predicted 20 year ago, has been confirmed experimentally and in simulation studies. The impact of the fluctuations on the functionality, yield, and reliability of the corresponding systems shifts the paradigm of the numerical device simulation. It becomes insufficient to simulate only one device representing one macroscopical design in a continuous charge approximation. An ensemble of macroscopically identical but microscopically different devices has to be characterized by simulation of statistically significant samples. The aims of the numerical simulations shift from predicting the characteristics of a single device with continuous doping towards estimating the mean values and the standard deviations of basic design parameters such as threshold voltage, subthreshold slope, transconductance, drive current, etc. for the whole ensemble of 'atomistically' different devices in the system. It has to be pointed out that even the mean values obtained from 'atomistic' simulations are not identical to the values obtained from continuous doping simulations. In this paper we present a hierarchical approach to the 'atomistic' simulation of aggressively scaled decanano MOSFETs. A full scale 3D drift-diffusion'atomostic' simulation approach is first described and used for verification of the more economical, but also more restricted, options. To reduce the processor time and memory requirements at high drain voltage we have developed a self-consistent option based on a thin slab solution of the current continuity equation only in the channel region. This is coupled to the Poisson's equation solution in the whole simulation domain in the Gummel iteration cycles. The accuracy of this approach is investigated in comparison with the full self-consistent solution. At low drain voltage only single solution of the nonlinear Poisson equation is sufficient to extract the current with satisfactory accuracy. A pilot version of a hydrodynamic 'atomistic' simulator has been developed in order to study the effect of the nonequilibrium, non local transport in decanano MOSFETs on the random dopant induced current fluctuations. For the first time we have also applied the density gradient approach in 3D to investigate the effect of the quantum confinement on the threshold voltage fluctuations. The developed 'atomistic' simulation techniques have been applied to study various fluctuation resistant MOSFET architectures including epitaxial and delta doped devices.

Asenov, Asen↗
NASA NTRS1973

VHF command system study

Solutions are provided to specific problems arising in the GSFC VHF-PSK and VHF-FSK Command Systems in support of establishment and maintenance of Data Systems Standards. Signal structures which incorporate transmission on the uplink of a clock along with the PSK or FSK data are considered. Strategies are developed for allocating power between the clock and data, and spectral analyses are performed. Bit error probability and other probabilities pertinent to correct transmission of command messages are calculated. Biphase PCM/PM and PCM/FM are considered as candidate modulation techniques on the telemetry downlink, with application to command verification. Comparative performance of PCM/PM and PSK systems is given special attention, including implementation considerations. Gain in bit error performance due to coding is also considered.

Gee, T. H.↗
NASA NTRS1975

Use of STS subsystems and components for MMSE, volume 1

Multiuse mission support equipment (MMSE) is flight/ground equipment for the shuttle era which is used in conjunction with more than one mission payload. Initial verification of STS subsystem's applicability to MMSE is provided along with the cost savings potential and programmatic data needed for further program planning decisions. Some 70 MMSE requirements were found to be potentially satisfied by STS equipment, and and 6 items of particular interest were chosen for special emphasis. All were found to be feasible and beneficial. Program cost savings through their use are estimated to be substantial. Further study is recommended to identify additional MMSE requirements and hardware.

Source record↗
NASA NTRS1993

Common Lunar Lander vehicle propulsion system conceptual design

The Common Lunar Lander (CLL) is a concept for a small, unpiloted vehicle which would provide a low-cost capability to land any of a variety of payloads in the 200 kg class at any point on the surface of the moon. Initiated as a precursor mission for the First Lunar Outpost, it also has considerable potential for use by the scientific community at large. A series of studies has been conducted at the NASA Johnson Space Center to define initial requirements and to initiate the design process. This paper describes the propulsion subsystem design as it existed at the CLL System Design Review. The propulsion subsystem design is described in detail along with the planned operations concept, including the unique concept of using pulsing of main engines for thrust modulation. Design options and trades considered and the verification process philosophy which was being planned for the program are discussed.

Hyatt, C. D.↗
NASA NTRS1997

NASA X-34 Technology in Motion

The X-34 technology development program is a joint industry/government project to develop, test, and operate a small, fully-reusable hypersonic flight vehicle. The objective is to demonstrate key technologies and operating concepts applicable to future reusable launch vehicles. Integrated in the vehicle are various systems to assure successful completion of mission objectives, including the Main Propulsion System (MPS). NASA-Marshall Space Flight Center (MSFC) is responsible for developing the X-34's MPS including the design and complete build package for the propulsion system components. The X-34 will be powered by the Fastrac Engine, which is currently in design and development at NASA-MSFC. Fastrac is a single-stage main engine, which burns a mixture of liquid oxygen (LOX) and kerosene(RP-1). The interface between the MPS and Fastrac engine are critical for proper system operation and technologies applicable to future reusable launch vehicles. Deneb's IGRIP software package with the Dynamic analysis option provided a key tool for conducting studies critical to this interface as well as a mechanism to drive the design of the LOX and RP-1 feedlines. Kinematic models were created for the Fastrac Engine and the feedlines for various design concepts. Based on the kinematic simulation within Envision, design and joint limits were verified and system interference controlled. It was also critical to the program to evaluate the effect of dynamic loads visually, providing a verification tool for dynamic analysis and in some cases uncovering areas that had not been considered. Deneb's software put the X-34 technology in motion and has been a key factor in facilitating the strenuous design schedule.

Beech, Geoffrey↗
NASA NTRS2007

Space Environment (Natural and Induced)

Considerable effort and improvement have been made in the study of ionizing radiation exposure occurring in various regions of space. Satellites and spacecrafts equipped with innovative instruments are continually refining particle data and providing more accurate information on the ionizing radiation environment. The major problem in accurate spectral definition of ionizing radiation appears to be the detailed energy spectra, especially at high energies, which is important parameter for accurate radiation risk assessment. Magnitude of risks posed by exposure to radiation in future space missions is subject to the accuracies of predictive forecast of event size of SPE, GCR environment, geomagnetic fields, and atmospheric radiation environment. Although heavy ion fragmentations and interactions are adequately resolved through laboratory study and model development, improvements in fragmentation cross sections for the light nuclei produced from HZE nuclei and their laboratory validation are still required to achieve the principal goal of planetary GCR simulation at a critical exposure site. More accurate prediction procedure for ionizing radiation environment can be made with a better understanding of the solar and space physics, fulfillment of required measurements for nuclear/atomic processes, and their validation and verification with spaceflights and heavy ion accelerators experiments. It is certainly true that the continued advancements in solar and space physics combining with physical measurements will strengthen the confidence of future manned exploration of solar system. Advancements in radiobiology will surely give the meaningful radiation hazard assessments for short and long term effects, by which appropriate and effective mitigation measures can be placed to ensure that humans safely live and work in the space, anywhere, anytime.

Kim, Myung-Hee Y.↗
NASA NTRS2008

Qualification Testing of Engineering Camera and Platinum Resistance Thermometer (PRT) Sensors for Mars Science Laboratory (MSL) Project under Extreme Temperatures to Assess Reliability and to Enhance Mission Assurance

Package Qualification and Verification (PQV) of advanced electronic packaging and interconnect technologies and various other types of qualification hardware for the Mars Exploration Rover/Mars Science Laboratory flight projects has been performed to enhance the mission assurance. The qualification of hardware (Engineering Camera and Platinum Resistance Thermometer, PRT) under extreme cold temperatures has been performed with reference to various project requirements. The flight-like packages, sensors, and subassemblies have been selected for the study to survive three times (3x) the total number of expected temperature cycles resulting from all environmental and operational exposures occurring over the life of the flight hardware including all relevant manufacturing, ground operations and mission phases. Qualification has been performed by subjecting above flight-like qual hardware to the environmental temperature extremes and assessing any structural failures or degradation in electrical performance due to either overstress or thermal cycle fatigue. Experiments of flight like hardware qualification test results have been described in this paper.

package reliability↗
NASA NTRS2014

Dissertation Defense: Computational Fluid Dynamics Uncertainty Analysis for Payload Fairing Spacecraft Environmental Control Systems

Spacecraft thermal protection systems are at risk of being damaged due to airflow produced from Environmental Control Systems. There are inherent uncertainties and errors associated with using Computational Fluid Dynamics to predict the airflow field around a spacecraft from the Environmental Control System. This paper describes an approach to quantify the uncertainty in using Computational Fluid Dynamics to predict airflow speeds around an encapsulated spacecraft without the use of test data. Quantifying the uncertainty in analytical predictions is imperative to the success of any simulation-based product. The method could provide an alternative to traditional validation by test only mentality. This method could be extended to other disciplines and has potential to provide uncertainty for any numerical simulation, thus lowering the cost of performing these verifications while increasing the confidence in those predictions.Spacecraft requirements can include a maximum airflow speed to protect delicate instruments during ground processing. Computational Fluid Dynamics can be used to verify these requirements; however, the model must be validated by test data. This research includes the following three objectives and methods. Objective one is develop, model, and perform a Computational Fluid Dynamics analysis of three (3) generic, non-proprietary, environmental control systems and spacecraft configurations. Several commercially available and open source solvers have the capability to model the turbulent, highly three-dimensional, incompressible flow regime. The proposed method uses FLUENT, STARCCM+, and OPENFOAM. Objective two is to perform an uncertainty analysis of the Computational Fluid Dynamics model using the methodology found in Comprehensive Approach to Verification and Validation of Computational Fluid Dynamics Simulations. This method requires three separate grids and solutions, which quantify the error bars around Computational Fluid Dynamics predictions. The method accounts for all uncertainty terms from both numerical and input variables. Objective three is to compile a table of uncertainty parameters that could be used to estimate the error in a Computational Fluid Dynamics model of the Environmental Control System spacecraft system.Previous studies have looked at the uncertainty in a Computational Fluid Dynamics model for a single output variable at a single point, for example the re-attachment length of a backward facing step. For the flow regime being analyzed (turbulent, three-dimensional, incompressible), the error at a single point can propagate into the solution both via flow physics and numerical methods. Calculating the uncertainty in using Computational Fluid Dynamics to accurately predict airflow speeds around encapsulated spacecraft in is imperative to the success of future missions.

Fluid Dynamics↗
NASA NTRS1992

Experimental code verification results for reflector antenna distortion compensation by array feeds

Electronic compensation of reflector surface distortion using array feed with individual amplitude and phase control of the array elements is becoming increasingly attractive because of the recent advances in monolithic microwave integrated circuit (MMIC) technology. An algorithm has been developed previously using the concept of focal plane conjugate field matching in the receive mode and a computer code has been generated that predicts the proper excitation coefficients for the elements of the reflector feed array to compensate the effects of reflector surface distortion. This paper presents the results of an experimental study to verify the above compensation algorithm and in general to demonstrate the effectiveness of the array feed compensation technique.

Zaman, A. J.↗
NASA NTRS1987

Space Station ground data management system

KSC is planning a Space Station Ground Data Management System (GDMS) for support of functional interface verification, integration and test of Space Station modules and elements. This computer system, planned for initial operational support in 1992, currently is entering a definition and prototyping stage. This paper provides an overview of the GDMS system concept. It synopsizes system functional capabilities, and discusses software and hardware architectural approaches currently under evaluation. It identifies programmatic constraints and their influence upon the concept, as well as specific technical issues planned for study or evaluation via prototyping.

Heuser, Jan↗
NASA NTRS2013

Computational Fluid Dynamics Uncertainty Analysis for Payload Fairing Spacecraft Environmental Control Systems

Spacecraft thermal protection systems are at risk of being damaged due to airflow produced from Environmental Control Systems. There are inherent uncertainties and errors associated with using Computational Fluid Dynamics to predict the airflow field around a spacecraft from the Environmental Control System. This proposal describes an approach to validate the uncertainty in using Computational Fluid Dynamics to predict airflow speeds around an encapsulated spacecraft. The research described here is absolutely cutting edge. Quantifying the uncertainty in analytical predictions is imperative to the success of any simulation-based product. The method could provide an alternative to traditional"validation by test only'' mentality. This method could be extended to other disciplines and has potential to provide uncertainty for any numerical simulation, thus lowering the cost of performing these verifications while increasing the confidence in those predictions. Spacecraft requirements can include a maximum airflow speed to protect delicate instruments during ground processing. Computationaf Fluid Dynamics can be used to veritY these requirements; however, the model must be validated by test data. The proposed research project includes the following three objectives and methods. Objective one is develop, model, and perform a Computational Fluid Dynamics analysis of three (3) generic, non-proprietary, environmental control systems and spacecraft configurations. Several commercially available solvers have the capability to model the turbulent, highly three-dimensional, incompressible flow regime. The proposed method uses FLUENT and OPEN FOAM. Objective two is to perform an uncertainty analysis of the Computational Fluid . . . Dynamics model using the methodology found in "Comprehensive Approach to Verification and Validation of Computational Fluid Dynamics Simulations". This method requires three separate grids and solutions, which quantify the error bars around Computational Fluid Dynamics predictions. The method accounts for all uncertainty terms from both numerical and input variables. Objective three is to compile a table of uncertainty parameters that could be used to estimate the error in a Computational Fluid Dynamics model of the Environmental Control System /spacecraft system. Previous studies have looked at the uncertainty in a Computational Fluid Dynamics model for a single output variable at a single point, for example the re-attachment length of a backward facing step. To date, the author is the only person to look at the uncertainty in the entire computational domain. For the flow regime being analyzed (turbulent, threedimensional, incompressible), the error at a single point can propagate into the solution both via flow physics and numerical methods. Calculating the uncertainty in using Computational Fluid Dynamics to accurately predict airflow speeds around encapsulated spacecraft in is imperative to the success of future missions.

Groves, Curtis E.↗
NASA NTRS2014

Dissertation Defense Computational Fluid Dynamics Uncertainty Analysis for Payload Fairing Spacecraft Environmental Control Systems

Spacecraft thermal protection systems are at risk of being damaged due to airflow produced from Environmental Control Systems. There are inherent uncertainties and errors associated with using Computational Fluid Dynamics to predict the airflow field around a spacecraft from the Environmental Control System. This paper describes an approach to quantify the uncertainty in using Computational Fluid Dynamics to predict airflow speeds around an encapsulated spacecraft without the use of test data. Quantifying the uncertainty in analytical predictions is imperative to the success of any simulation-based product. The method could provide an alternative to traditional "validation by test only" mentality. This method could be extended to other disciplines and has potential to provide uncertainty for any numerical simulation, thus lowering the cost of performing these verifications while increasing the confidence in those predictions. Spacecraft requirements can include a maximum airflow speed to protect delicate instruments during ground processing. Computational Fluid Dynamics can be used to verify these requirements; however, the model must be validated by test data. This research includes the following three objectives and methods. Objective one is develop, model, and perform a Computational Fluid Dynamics analysis of three (3) generic, non-proprietary, environmental control systems and spacecraft configurations. Several commercially available and open source solvers have the capability to model the turbulent, highly three-dimensional, incompressible flow regime. The proposed method uses FLUENT, STARCCM+, and OPENFOAM. Objective two is to perform an uncertainty analysis of the Computational Fluid Dynamics model using the methodology found in "Comprehensive Approach to Verification and Validation of Computational Fluid Dynamics Simulations". This method requires three separate grids and solutions, which quantify the error bars around Computational Fluid Dynamics predictions. The method accounts for all uncertainty terms from both numerical and input variables. Objective three is to compile a table of uncertainty parameters that could be used to estimate the error in a Computational Fluid Dynamics model of the Environmental Control System /spacecraft system. Previous studies have looked at the uncertainty in a Computational Fluid Dynamics model for a single output variable at a single point, for example the re-attachment length of a backward facing step. For the flow regime being analyzed (turbulent, three-dimensional, incompressible), the error at a single point can propagate into the solution both via flow physics and numerical methods. Calculating the uncertainty in using Computational Fluid Dynamics to accurately predict airflow speeds around encapsulated spacecraft in is imperative to the success of future missions.

CFD↗
NASA NTRS2010

Ongoing Study of Supersonic Retro-Propulsion Using Structured Overset Grids and OVERFLOW

The interest in supersonic retro-propulsion (SRP) as a means of deceleration during planetary entry increases with the desire to land high mass vehicles on Mars. Since it is difficult to obtain flight data or properly simulate this type of flow field in a wind tunnel, the use of computational fluid dynamics (CFD) becomes increasingly important, as does the need to verify the current CFD methods. This presentation will show results from structured overset grids and OVERFLOW, a Reynolds Averaged Navier-Stokes solver, obtained during the continuing CFD verification process. Flow structure, surface pressure, forces, and moments are compared to historic and modern wind tunnel data as well as to other Navier-Stokes solvers, DPLR and FUN3D. Cases include single and multiple nozzle cases from the Jarvinen and Adams experiment,i the Daso et al experiment, and a recent test in the NASA Langley Unitary Wind Tunnel (scheduled for June 2010).

Schauerhamer, Daniel Guy↗