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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 991 records · Page 55
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Mode shape analysis using a commercially available peak store video frame buffer

Time exposure photography, sometimes coupled with strobe illumination, is an accepted method for motion analysis that bypasses frame by frame analysis and resynthesis of data. Garden variety video cameras can now exploit this technique using a unique frame buffer that is a non-integrating memory that compares incoming data with that already stored. The device continuously outputs an analog video signal of the stored contents which can then be redigitized and analyzed using conventional equipment. Historically, photographic time exposures have been used to record the displacement envelope of harmonically oscillating structures to show mode shape. Mode shape analysis is crucial, for example, in aeroelastic testing of wind tunnel models. Aerodynamic, inertial, and elastic forces can couple together leading to catastrophic failure of a poorly designed aircraft. This paper will explore the usefulness of the peak store device as a videometric tool and in particular discuss methods for analyzing a targeted vibrating plate using the 'peak store' in conjunction with calibration methods familiar to the close-range videometry community. Results for the first three normal modes will be presented.

Snow, Walter L.↗
NASA NTRS2006

Establishment and Implementation of a Close Approach Evaluation and Avoidance Process for Earth Observing System Missions

In the fall of 2004, the Earth Science Mission Operations Project tasked the Goddard Space Flight Center (GSPC) Flight Dynamics Analysis Branch with establishment of a process to protect the high-value Earth Observing System (EOS) missions (Terra, Aqua, and Aura) from close approaches with space debris and other orbiting objects. An agreement between GSFC and the United States Strategic Command was put in place so that close approach predictions would be routinely generated. This paper describes the ESMO conjunction assessment process for the EOS satellites. Process details, including tools and algorithms developed, are discussed. Particular details for a predicted close approach between Terra and a piece of space debris that resulted in the execution of a debris avoidance maneuver are included. This close approach example is described in detail fiom the first screening identification through execution of the mitigation maneuver to illustrate both the process and lessons learned fiom its implementation.

Newman, Lauri↗
NASA NTRS2013

Enhanced Schapery Theory Software Development for Modeling Failure of Fiber-Reinforced Laminates

Progressive damage and failure analysis (PDFA) tools are needed to predict the nonlinear response of advanced fiber-reinforced composite structures. Predictive tools should incorporate the underlying physics of the damage and failure mechanisms observed in the composite, and should utilize as few input parameters as possible. The purpose of the Enhanced Schapery Theory (EST) was to create a PDFA tool that operates in conjunction with a commercially available finite element (FE) code (Abaqus). The tool captures the physics of the damage and failure mechanisms that result in the nonlinear behavior of the material, and the failure methodology employed yields numerical results that are relatively insensitive to changes in the FE mesh. The EST code is written in Fortran and compiled into a static library that is linked to Abaqus. A Fortran Abaqus UMAT material subroutine is used to facilitate the communication between Abaqus and EST. A clear distinction between damage and failure is imposed. Damage mechanisms result in pre-peak nonlinearity in the stress strain curve. Four internal state variables (ISVs) are utilized to control the damage and failure degradation. All damage is said to result from matrix microdamage, and a single ISV marks the micro-damage evolution as it is used to degrade the transverse and shear moduli of the lamina using a set of experimentally obtainable matrix microdamage functions. Three separate failure ISVs are used to incorporate failure due to fiber breakage, mode I matrix cracking, and mode II matrix cracking. Failure initiation is determined using a failure criterion, and the evolution of these ISVs is controlled by a set of traction-separation laws. The traction separation laws are postulated such that the area under the curves is equal to the fracture toughness of the material associated with the corresponding failure mechanism. A characteristic finite element length is used to transform the traction-separation laws into stress-strain laws. The ISV evolution equations are derived in a thermodynamically consistent manner by invoking the stationary principle on the total work of the system with respect to each ISV. A novel feature is the inclusion of both pre-peak damage and appropriately scaled, post-peak strain softening failure. Also, the characteristic elements used in the failure degradation scheme are calculated using the element nodal coordinates, rather than simply the square root of the area of the element.

Pineda, Evan J.↗
NASA NTRS1986

Solution of nonlinear finite difference ocean models by optimization methods with sensitivity and observational strategy analysis

The paper studies with finite difference nonlinear circulation models the uncertainties in interesting flow properties, such as western boundary current transport, potential and kinetic energy, owing to the uncertainty in the driving surface boundary condition. The procedure is based upon nonlinear optimization methods. The same calculations permit quantitative study of the importance of new information as a function of type, region of measurement and accuracy, providing a method to study various observing strategies. Uncertainty in a model parameter, the bottom friction coefficient, is studied in conjunction with uncertain measurements. The model is free to adjust the bottom friction coefficient such that an objective function is minimized while fitting a set of data to within prescribed bounds. The relative importance of the accuracy of the knowledge about the friction coefficient with respect to various kinds of observations is then quantified, and the possible range of the friction coefficients is calculated.

Schroeter, Jens↗
NASA NTRS2013

Application of CO2 Snow Jet Cleaning in Conjunction with Laboratory Based Total Reflection X-Ray Fluorescence

The Genesis mission was the first mission returning solar material to Earth since the Apollo program [1,2]. Unfortunately the return of the space craft on September 8, 2004 resulted in a crash landing, which shattered the samples into small fragments and exposed them to desert soil and other debris. Thus only small fragments of the original collectors are available, each having different degrees of surface contamination. Thorough surface cleaning is required to allow for subsequent analysis of solar wind material embedded within. An initial cleaning procedure was developed in coordination with Johnson Space Center which focused on removing larger sized particulates and a thin film organic contamination acquired during collection in space [3]. However, many of the samples have additional residues and more rigorous and/or innovative cleaning steps might be necessary. These cleaning steps must affect only the surface to avoid leaching and re-distribution of solar wind material from the bulk of the collectors. To aid in development and identification of the most appropriate cleaning procedures each sample has to be thoroughly inspected before and after each cleaning step. Laboratory based total reflection X-ray fluorescence (TXRF) spectrometry lends itself to this task as it is a non-destructive and surface sensitive analytical method permitting analysis of elements from aluminum onward present at and near the surface of a flat substrate [4]. The suitability of TXRF has been demonstrated for several Genesis solar wind samples before and after various cleaning methods including acid treatment, gas cluster ion beam, and CO2 snow jet [5 - 7]. The latter one is non-invasive and did show some promise on one sample [5]. To investigate the feasibility of CO2 snow jet cleaning further, several flown Genesis samples were selected to be characterized before and after CO2 snow application with sample 61052 being discussed below.

Schmeling, M.↗
NASA NTRS2003

Turbulence Lidar Development Status

This viewgraph provides an overview of efforts conducted by Coherent Technologies, Inc. in conjunction with NASA Langley Research Center to develop a robust turbulence detection capability that spans full range of turbulence environments. Topics covered include: general principles of infrared doppler radar (lidar) turbulence measurement, performance simulation, complete detection capability provided by dual wavelength radar, algorithm development, technology development needs and turbulence detection problems. Versions of this turbulence lidar system were flight tested. Data analysis from these flight tests are presented. Future flight tests aboard DC-8 and B-757 are planned as well as continued algorithm development and performance simulation activities.

Clark, Ivan↗
NASA NTRS2016

HESTIA Phase I Test Results: The Air Revitalization System

In any human spaceflight mission, a number of Environmental Control & Life Support System (ECLSS) technologies work together to provide the conditions astronauts need to live healthily, productively, and comfortably in space. In a long-duration mission, many of these ECLSS technologies may use materials supplied by In-Situ Resource Utilization (ISRU), introducing more interactions between systems. The Human Exploration Spacecraft Test-bed for Integration & Advancement (HESTIA) Project aims to create a test-bed to evaluate ECLSS and ISRU technologies and how they interact in a high-fidelity, closed-loop, human-rated analog habitat. Air purity and conditioning are essential components within any ECLSS and for HESTIA's first test they were achieved with the Air Revitalization System (ARS) described below. The ARS provided four essential functions to the test-bed chamber: cooling the air, removing humidity from the air, removing trace contaminants, and scrubbing carbon dioxide (CO2) from the air. In this case, the oxygen supply function was provided by ISRU. In the current configuration, the ARS is a collection of different subsystems. A fan circulates the air, while a condensing heat exchanger (CHX) pulls humidity out of the air. A Trace Contaminant Removal System (TCRS) filters the air of potentially harmful contaminants. Lastly, a Reactive Plastic Lithium Hydroxide (RP-LiOH) unit removes CO2 from the breathing air. During the HESTIA Phase I test in September 2015, the ARS and its individual components each functioned as expected, although further analysis is underway. During the Phase I testing and in prior bench-top tests, the energy balance of heat removed by the CHX was not equal to the cooling it received. This indicated possible instrument error and therefore recalibration of the instruments and follow-up testing is planned in 2016 to address the issue. The ARS was tested in conjunction with two other systems: the Human Metabolic Simulator (HMS) and the Electrolyzer. They behaved as anticipated as well. The HMS added humidity, CO2, and heat to the chamber while removing oxygen, and the Electrolyzer (an ISRU technology) added oxygen. The objective for HESTIA in 2015 was achieved: the creation of a high-fidelity test-bed for ECLSS and ISRU technologies. With the 'backbone' technologies installed, more technologies will be added to increase the analog habitat's fidelity over the next few years. The ARS was designed with this in mind, and as new technologies develop and mature, the strategic installation of the existing components will allow for them to be replaced with the new technologies.

Wright, Sarah E.↗
NASA NTRS1982

Observation of a heated electron population associated with the 6300 A SAR arc emission

Conjunctive observations of the Dynamics Explorer satellite pair and the Pacific Northwest Laboratory scanning photometer unit at Richland, WA have allowed identification of the low energy, heated, electron population associated with the 6300 A Stable Auroral Red (SAR) arc emission. Measurements over the SAR arc on day 296 of 1981 show an enhanced flux in the low altitude 5-12 eV electrons. Analysis of this electron population shows them to be fairly Maxwellian, with temperatures on the order of 9900 + or - 1100 K and an earthward field aligned velocity of approximately 275 + or - 60 km/sec. The electrons are not accompanied by ion precipitation. The ion loss cone is empty at least as high as 6000 km. This fact may cast some doubt as to the role of the ring current ions in the SAR arc production.

Gurgiolo, C.↗
NASA NTRS1986

In-flight identification of the Galileo spacecraft flexible mode characteristics

The scan platform of the Galialan spacecraft is attached to a flexible stator structure that separates the actuator from the platform-mounted inartial sensor. A scheme to identify the flexible mode characteristics (frequency, damping, and modal coefficient) of the stator using flight data is presentevd. A frequency domain analysis approach is taken and the identified mode characteristics will be used for updating the scan platform controler parameters. The influence of structural flexibility to th s can controller design is explained and the constraints in experting the identification procedure in flight are discused. Computer simulation results of the identification scheme are presented. The scheme in further verified by DISCOS simulations, in conjunction witha full spacecraft dynamics model and the scan platform controllers.

Wang, F. C.↗
NASA NTRS1992

OPAD status report - Investigation of SSME component erosion

Significant erosion of preburner faceplates was observed during recent SSME test firings at the NASA Technology Test Bed (TTB). The OPAD instrumentation acquired exhaust-plume spectral data during each test which indicate the occurrence of metallic species consistent with faceplate component composition. A qualitative analysis of the spectral data was conducted to evaluate the state of the engine versus time for each test according to the nominal conditions of TTB firing number 17 and number 18. In general the analyses indicate abnormal erosion levels at or near startup. Subsequent to the initial erosion event, signal levels tend to decrease towards nominal baseline values. These findings, in conjunction with post-test engine inspections, suggest that in cases under study, the erosion may not have been catastrophic to the immediate operation of the engine.

Powers, W. T.↗
NASA NTRS1993

The flight performance of the Galileo orbiter USO

Results are presented from an analysis of radio metric data received by the DSN stations from the Galileo spacecraft using an Ultrastable Oscillator (USO) as a signal source. These results allow the health and performance of the Galileo USO to be evaluated, and are used to calibrate this Radio Science instrument and the data acquired for Radio Science experiments such as the Red-shift Observation, Solar Conjunction, and Jovian occultations. Estimates for the USO-referenced spacecraft-transmitted frequency and frequency stability were made for 82 data acquisition passes conducted between launch (October 1989) and November 1991. Analyses of the spacecraft-transmitted frequencies show that the USO is behaving as expected. The USO was powered off and then back on in August 1991 with no adverse effect on its performance. The frequency stabilities measured by Allan deviation are consistent with expected values due to thermal wideband noise and the USO itself at the appropriate time intervals. The Galileo USO appears to be healthy and functioning normally in a reasonable manner.

Morabito, D. D.↗
NASA NTRS2006

Dynamics and Adaptive Control for Stability Recovery of Damaged Aircraft

This paper presents a recent study of a damaged generic transport model as part of a NASA research project to investigate adaptive control methods for stability recovery of damaged aircraft operating in off-nominal flight conditions under damage and or failures. Aerodynamic modeling of damage effects is performed using an aerodynamic code to assess changes in the stability and control derivatives of a generic transport aircraft. Certain types of damage such as damage to one of the wings or horizontal stabilizers can cause the aircraft to become asymmetric, thus resulting in a coupling between the longitudinal and lateral motions. Flight dynamics for a general asymmetric aircraft is derived to account for changes in the center of gravity that can compromise the stability of the damaged aircraft. An iterative trim analysis for the translational motion is developed to refine the trim procedure by accounting for the effects of the control surface deflection. A hybrid direct-indirect neural network, adaptive flight control is proposed as an adaptive law for stabilizing the rotational motion of the damaged aircraft. The indirect adaptation is designed to estimate the plant dynamics of the damaged aircraft in conjunction with the direct adaptation that computes the control augmentation. Two approaches are presented 1) an adaptive law derived from the Lyapunov stability theory to ensure that the signals are bounded, and 2) a recursive least-square method for parameter identification. A hardware-in-the-loop simulation is conducted and demonstrates the effectiveness of the direct neural network adaptive flight control in the stability recovery of the damaged aircraft. A preliminary simulation of the hybrid adaptive flight control has been performed and initial data have shown the effectiveness of the proposed hybrid approach. Future work will include further investigations and high-fidelity simulations of the proposed hybrid adaptive Bight control approach.

Nguyen, Nhan↗
NASA NTRS2015

Mock Certification Basis for an Unmanned Rotorcraft for Precision Agricultural Spraying

This technical report presents the results of a case study using a hazard-based approach to develop preliminary design and performance criteria for an unmanned agricultural rotorcraft requiring airworthiness certification. This case study is one of the first in the public domain to examine design and performance criteria for an unmanned aircraft system (UAS) in tandem with its concept of operations. The case study results are intended to support development of airworthiness standards that could form a minimum safety baseline for midsize unmanned rotorcraft performing precision agricultural spraying operations under beyond visual line-of-sight conditions in a rural environment. This study investigates the applicability of current methods, processes, and standards for assuring airworthiness of conventionally piloted (manned) aircraft to assuring the airworthiness of UAS. The study started with the development of a detailed concept of operations for precision agricultural spraying with an unmanned rotorcraft (pp. 5-18). The concept of operations in conjunction with a specimen unmanned rotorcraft were used to develop an operational context and a list of relevant hazards (p. 22). Minimum design and performance requirements necessary to mitigate the hazards provide the foundation of a proposed (or mock) type certification basis. A type certification basis specifies the applicable standards an applicant must show compliance with to receive regulatory approval. A detailed analysis of the current airworthiness regulations for normal-category rotorcraft (14 Code of Federal Regulations, Part 27) was performed. Each Part 27 regulation was evaluated to determine whether it mitigated one of the relevant hazards for the specimen UAS. Those regulations that did were included in the initial core of the type certification basis (pp. 26-31) as written or with some simple modifications. Those regulations that did not mitigate a recognized hazard were excluded from the certification basis. The remaining regulations were applicable in intent, but the text could not be easily tailored. Those regulations were addressed in separate issue papers. Exploiting established regulations avoids the difficult task of generating and interpreting novel requirements, through the use of acceptable, standardized language. The rationale for the disposition of the regulations was assessed and captured (pp. 58-115). The core basis was then augmented by generating additional requirements (pp. 38-47) to mitigate hazards for an unmanned sprayer that are not covered in Part 27.

Hayhurst, Kelly J.↗
NASA NTRS1977

Short-term variations of the galactic cosmic ray intensity - 1964-1967

A statistical analysis of time variations in ground-level nucleonic cosmic-ray intensity for the interval from 1964 to 1967 is presented which incorporates synoptic observations of the solar white-light corona as well as indices of photospheric and chromospheric activity. Correlation analysis of solar activity and short-term modulation reveals that all indices vary significantly on time scales near the solar rotation period and that the correlation function exhibits a quasi-sinusoidal variation that maximizes near zero lag. It is found that 27-day variations of the indices were most pronounced in 1966-1967, that recurrent cosmic-ray depressions occurred in conjunction with observed solar-wind disturbances, and that two categories of interplanetary disturbance are sufficient to account for the large recurrent cosmic-ray depressions in 1966-1967. It is suggested that flare-generated shocks were the main source of these recurrent cosmic-ray variations and that the contribution of corotating cosmic-ray disturbances to the observed recurrent modulation was probably very small. This hypothesis is tested against the correlation functions of solar and cosmic-ray indices.

Parker, G. D.↗
NASA NTRS1978

Study of low-cost fabrication methods for aerospace composite materials

Flat and hat section specimens of graphite/epoxy composite materials have been fabricated by the resin bath or wet pultrusion process. This demonstrated the feasibility of incorporating crossplied graphite fiber reinforcements in conjunction with epoxy resin systems in the wet pultrusion process. However, the thickness constraints of the pultrusion process, the lack of dimensional stability of the crossply materials and equipment limitations affect the quality of the hat section pultrusions. The wet pultrusion process shows promise of being a low cost method for producing composite parts with constant cross section along the length. A cost analysis showed at least 80 percent cost reduction for the hat section and 40 percent for flat panel by pultrusion over the conventional manual and automated lay-up.

Chung, H. H.↗
NASA NTRS1982

Evaluation of an improved finite-element thermal stress calculation technique

A procedure for generating accurate thermal stresses with coarse finite element grids (Ojalvo's method) is described. The procedure is based on the observation that for linear thermoelastic problems, the thermal stresses may be envisioned as being composed of two contributions; the first due to the strains in the structure which depend on the integral of the temperature distribution over the finite element and the second due to the local variation of the temperature in the element. The first contribution can be accurately predicted with a coarse finite-element mesh. The resulting strain distribution can then be combined via the constitutive relations with detailed temperatures from a separate thermal analysis. The result is accurate thermal stresses from coarse finite element structural models even where the temperature distributions have sharp variations. The range of applicability of the method for various classes of thermostructural problems such as in-plane or bending type problems and the effect of the nature of the temperature distribution and edge constraints are addressed. Ojalvo's method is used in conjunction with the SPAR finite element program. Results are obtained for rods, membranes, a box beam and a stiffened panel.

Camarda, C. J.↗
NASA NTRS1984

Venus Radar Mapper orbit accuracy analysis

Spacecraft orbital accuracies during the mapping phase of the Venus Radar Mapper Mission are the subject of this paper. The analysis presented describes the navigational strategy for the prime mission in support of mapping the planet Venus using a spacecraft deployed Synthetic Aperture Radar. Achievable orbital accuracies are shown to be limited by accuracy of interferometric data to be used. Implications of tracking system configurations and of expected degradation in data accuracy towards the end of the mission in the proximity of superior solar conjunction are examined.

Mohan, S. N.↗
NASA NTRS1992

Turbulence indicators for Space Shuttle launches

A report on the research and analysis for identifying turbulent regions from the surface to 16 km for Space Shuttle launches is presented. The research demonstrates that the results from the FPS-16 radar/jimsphere balloon system in measuring winds can indicate the presence of or conditions ripe for turbulence in the troposphere and lower stratosphere. It is shown that atmospheric data obtained during the Shuttle launches by the rawinsonde in conjunction with the jimsphere provide the necessary meteorological data to compute aerodynamic parameters to identify turbulence.

Susko, Michael↗