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At least 1,117 records · Page 62
All sourcesNASA NTRSDOE OSTI
NASA NTRS2023

First Principles Modeling of the Thermal Amine Scrubber Flight Experiment’s Chemical Performance

The removal of atmospheric CO2 from a spacecraft is of particular importance to NASA’s mission, and is an area of continual study and technological advancement. One of the more recent advancements has been with reusable sorbents being regenerated with a combination of heat and vacuum. One such technology is the Thermal Amine Scrubber (TAS) flight experiment on the ISS, though several others are currently flying or preparing to fly. A model was created of the TAS to predict chemical performance, using fundamental chemistry and physics based on principles rather than empirical relations. Since the physical laws are true across all conditions, such a model enables greater model accuracy outside the bounds of test data, and allows for virtual testing of the hardware at conditions that are prohibitively difficult or expensive to actually test. This paper details the model’s development, operation, and correlation to data from the flight unit. The model is then compared to a data set taken from the flight unit under different flow, CO2 partial pressure, and bed configuration conditions, resulting in only a 2% error. The equations and principles laid forth in this paper are applicable to a wide range of thermally regenerated sorbents, and additional models of a similar nature would allow for potentially the most straightforward and direct method of comparison of technologies available to date.

CO2 removal↗
NASA NTRS1988

Hypervelocity impact damage assessment for Space Station

To inhibit damage and limit the probability of penetration of the Space Station pressure wall by micrometeoroids and orbital debris, a shield placed away from the wall is used to form a double wall. To determine shield effectiveness and assess impact damage, existing test data were reviewed and additional testing was performed for Space Station double wall designs. Empirical spallation and penetration functions derived from the data show that shield thickness and impact angle affect the damage to the wall. Thick shields reduce wall damage for low angle impacts but increase damage for oblique impacts. Multilayer insulation between the shield and wall reduces impact damage to the wall. A relationship between impact velocity and spall damage to the wall is demonstrated. Preliminary test results on Li-Al shield material indicate possible improved effectiveness over Al shields.

Coronado, Alex R.↗
NASA NTRS1996

Thrust Vectoring on the NASA F-18 High Alpha Research Vehicle

Investigations into a multiaxis thrust-vectoring system have been conducted on an F-18 configuration. These investigations include ground-based scale-model tests, ground-based full-scale testing, and flight testing. This thrust-vectoring system has been tested on the NASA F-18 High Alpha Research Vehicle (HARV). The system provides thrust vectoring in pitch and yaw axes. Ground-based subscale test data have been gathered as background to the flight phase of the program. Tests investigated aerodynamic interaction and vane control effectiveness. The ground-based full-scale data were gathered from static engine runs with image analysis to determine relative thrust-vectoring effectiveness. Flight tests have been conducted at the NASA Dryden Flight Research Center. Parameter identification input techniques have been developed. Individual vanes were not directly controlled because of a mixer-predictor function built into the flight control laws. Combined effects of the vanes have been measured in flight and compared to combined effects of the vanes as predicted by the cold-jet test data. Very good agreement has been found in the linearized effectiveness derivatives.

Bowers, Albion H.↗
NASA NTRS1995

Data-Logger Interface And Test Controller

Data-logger interface and test controller developed to enable automation of tests in conjunction with data-acquisition functions performed by data loggers that have output-switching capabilities. Includes relay logic circuits that remain deenergized until out-of-tolerance condition on any data channel discovered. Designed to be connected to Fluke model 2286A (or equivalent) data-logger system, which features 3 control channels with 6 data inputs per channel. Includes elapsed-time counter that keeps track of power outages.

Burch, Donnie R.↗
NASA NTRS2002

Influence of Small Steps on Wall Pressure Fluctuation Spectra Measured on Tu-144LL Flying Laboratory

Results of analyzing flight-test data of pressure-fluctuation fields in front of forward-facing steps and behind backward-facing steps are presented. The range of dimensionless step heights (normalized by boundary-layer displacement thickness) in the flight test was 0.042-0.236. The flight tests covered a mach-number range from 0.57 to 1.97. In the mach-number ranges covered by wind-tunnel tests (0.57 to 0.78 and 1.5 to 2) data agree very well with the flight data. Very importantly, the flight-test data fill in the gap previously existing for small-step pressure-fluctuations in the range of mach 0.78 to 1.5. Increased pressure-fluctuations were observed in the transonic region.

Efimtsov, B. M.↗
NASA NTRS1997

[Activities of the Department of Electrical Engineering, Howard University]

Theoretical derivations, computer analysis and test data are provided to demonstrate that the cavity model is a feasible one to analyze thin-substrate, rectangular-patch microstrip antennas. Seven separate antennas were tested. Most of the antennas were designed to resonate at L-band frequencies (1-2 GHz). One antenna was designed to resonate at an S-band (2-4 GHz) frequency of 2.025 GHz. All dielectric substrates were made of Duroid, and were of varying thicknesses and relative dielectric constant values. Theoretical derivations to calculate radiated free space electromagnetic fields and antenna input impedance were performed. MATHEMATICA 2.2 software was used to generate Smith Chart input impedance plots, normalized relative power radiation plots and to perform other numerical manipulations. Network Analyzer tests were used to verify the data from the computer programming (such as input impedance and VSWR). Finally, tests were performed in an anechoic chamber to measure receive-mode polar power patterns in the E and H planes. Agreement between computer analysis and test data is presented. The antenna with the thickest substrate (e(sub r) = 2.33,62 mils thick) showed the worst match to theoretical impedance data. This is anticipated due to the fact that the cavity model generally loses accuracy when the dielectric substrate thickness exceeds 5% of the antenna's free space wavelength. A method of reducing computer execution time for impedance calculations is also presented.

Yalamanchili, Raj C.↗
NASA NTRSDate not supplied

Monocular Ranging for Small Unmanned Aerial Systems in the Far-Field

Recent proliferation of small Unmanned Aerial Systems (sUAS) applications requires onboard collision avoidance systems to mitigate the risk of collision with non-cooperative aircraft and manned aircraft, which may not see sUAS in time to perform an avoidance maneuver. An attractive avenue for onboard collision avoidance is the utilization of machine vision cameras due to their low size, weight and power (SWaP) requirements. In this paper, we characterize the range performance of a machine vision system developed in-house and mounted onto an sUAS. The technique was designed to estimate the performance of a sense-and-avoid system to ensure that the sensing components meet the well-clear requirements for the chosen platform and avoidance strategy. Experimental flight-test data was acquired from test-flights flown along multiple collision geometries for two intruders: a general Aviation (GA) aircraft and a fixed-wing sUAS. The ownship and both intruders were instrumented with inertial navigation systems (INS) recording position and attitude information. The range at first detection, 𝑹𝟎, was extracted from in-flight imagery of head-on collision course geometry synchronized with INS data from both aircraft and ground-truth values extracted from the raw imagery. This initial detection distance, 𝑹𝟎, scales with atmospheric attenuation. Therefore, under clear sky conditions, the derived 𝑹𝟎 value represents the upper bound on the detection range achievable by the test configuration of the detector. Results indicate that the maximum initial detection distance for a 4k resolution action camera fitted with a 41º Field of View (FOV) lens is 2.763 ± 0.037 km for a GA aircraft and 0.881 ± 0.061 km for a fixed-wing sUAS, respectively. The in results this study suggest that a vision-based detect and track system may be analyzed using the sensor characterization and contextualized within aircraft well-clear volumes.

Chester V. Dolph↗
NASA NTRS2009

Exploring Modeling Options and Conversion of Average Response to Appropriate Vibration Envelopes for a Typical Cylindrical Vehicle Panel with Rib-stiffened Design

Although applications for Statistical Energy Analysis (SEA) techniques are more widely used in the aerospace industry today, opportunities to anchor the response predictions using measured data from a flight-like launch vehicle structure are still quite valuable. Response and excitation data from a ground acoustic test at the Marshall Space Flight Center permitted the authors to compare and evaluate several modeling techniques available in the SEA module of the commercial code VA One. This paper provides an example of vibration response estimates developed using different modeling approaches to both approximate and bound the response of a flight-like vehicle panel. Since both vibration response and acoustic levels near the panel were available from the ground test, the evaluation provided an opportunity to learn how well the different modeling options can match band-averaged spectra developed from the test data. Additional work was performed to understand the spatial averaging of the measurements across the panel from measured data. Finally an evaluation/comparison of two conversion approaches from the statistical average response results that are output from an SEA analysis to a more useful envelope of response spectra appropriate to specify design and test vibration levels for a new vehicle.

Harrison, Phil↗
NASA NTRS1995

Accelerated Test Methods

Neural network systems were evaluated for use in predicting wear of mechanical systems. Three different neural network software simulation packages were utilized in order to create models of tribological wear tests. Representative simple, medium, and high complexity simulation packages were selected. Pin-on-disk, rub shoe, and four-ball tribological test data was used for training, testing, and verification of the neural network models. Results showed mixed success. The neural networks were able to predict results with some accuracy if the number of input variables was low or the amount of training data was high. Increased neural network complexity resulted in more accurate results, however there was a point of diminishing return. Medium complexity models were the best trade off between accuracy and computing time requirements. A NASA Technical Memorandum and a Society of Tribologists and Lubrication Engineers paper are being published which detail the work.

Jansen, Ralph↗
NASA NTRS1994

Measurement of Residual Flexibility for Substructures Having Prominent Flexible Interfaces

Verification of a dynamic model of a constrained structure requires a modal survey test of the physical structure and subsequent modification of the model to obtain the best agreement possible with test data. Constrained-boundary or fixed-base testing has historically been the most common approach for verifying constrained mathematical models, since the boundary conditions of the test article are designed to match the actual constraints in service. However, there are difficulties involved with fixed-base testing, in some cases making the approach impractical. It is not possible to conduct a truly fixed-base test due to coupling between the test article and the fixture. In addition, it is often difficult to accurately simulate the actual boundary constraints, and the cost of designing and constructing the fixture may be prohibitive. For use when fixed-base testing proves impractical or undesirable, alternate free-boundary test methods have been investigated, including the residual flexibility technique. The residual flexibility approach has been treated analytically in considerable detail and has had limited frequency response measurements for the method. This concern is well-justified for a number of reasons. First, residual flexibilities are very small numbers, typically on the order of 1.0E-6 in/lb for translational diagonal terms, and orders of magnitude smaller for off-diagonal values. This poses difficulty in obtaining accurate and noise-free measurements, especially for points removed from the excitation source. A second difficulty encountered in residual measurements lies in obtaining a clean residual function in the process of subtracting synthesized modal data from a measured response function. Inaccuracies occur since modes are not subtracted exactly, but only to the accuracy of the curve fits for each mode; these errors are compounded with increasing distance from the excitation point. In this paper, the residual flexibility method is applied to a simple structure in both test and analysis. Measured and predicted residual functions are compared, and regions of poor data in the measured curves are described. It is found that for accurate residual measurements, frequency response functions having prominent stiffness lines in the acceleration/force format are needed. The lack of such stiffness lines increases measurement errors. Interface drive point frequency respose functions for shuttle orbiter payloads exhibit dominant stiffness lines, making the residual test approach a good candidate for payload modal tests when constrained tests are inappropriate. Difficulties in extracting a residual flexibility value from noisy test data are discussed. It is shown that use of a weighted second order least-squares curve fit of the measured residual function allows identification of residual flexibility that compares very well with predictions for the simple structure. This approach also provides an estimate of second order residual mass effects.

Tinker, Michael L.↗
NASA NTRS1975

Project space shuttle. Data bus evaluation laboratory test report

A Data Bus Evaluation Laboratory (DBEL) facility has been established to test and evaluate space shuttle data bus hardware. Performance testing conducted on an in-house developed multiplex interface adapter for the purpose of evaluating DBEL test procedures, test hardware, and test software in a realistic test environment is described. Results are presented.

Dennis, G. R.↗
NASA NTRS1980

Statistical fatigue of unnotched composite laminates

A general analytical, phenomenological model is developed for characterizing fatigue damage accumulation in unnotched composite laminates, and experimental results are used to evaluate the model. The fatigue model, which is developed for various types of cyclic loadings, is based on the assumption that the residual strength reduction is a monotonically decreasing function of the fatigue life. Parameters are determined from baseline test data consisting of one set of residual strength data, one set of static strength data, and one set of constant amplitude fatigue life data. Once the parameters are determined, the model is able to predict: (1) the statistical distribution of the fatigue life, and the residual strength under constant and variable amplitude loads, and (2) the effect of periodic proof tests, without any additional experimental data. Experimental test results show that predictions made from the present model agree quite well with the experimental results. The model is also applicable to fatigue of bonded or bolted composite joints.

Yang, J. N.↗
NASA NTRSDate not supplied

Nodal Numerical Modeling of Submerged Helium Injection in a Cryogenic Propellant Tank

Subcooling of cryogenic propellant by helium injection is one of the most effective methods for suppressing bulk boiling and keeping subcooled propellant conditions for pre-launch, launch, and post-launch pressurization applications. For tank pressurization, submerged helium injection can substantially reduce helium consumption by infusing gaseous propellant into the tank ullage. This paper presents a mathematical model of the helium bubbling process in liquid oxygen to estimate the amount of oxygen vapor absorbed by the rising helium bubbles and the amount of subcooling of liquid oxygen due to evaporative heat and mass transfer. This mathematical model was incorporated in a simulation model of tank pressurization built with Generalized Fluid System Simulation Program (GFSSP), a general-purpose flow network code developed at NASA/Marshall Space Flight Center. The numerical predictions of subcooling have been compared with the experimental data of Cho et al. which investigated the propellant subcooling effect as a function of system pressure, helium injection temperature, and flowrate for a non-drained submerged injection system. The numerical predictions of helium consumption have been compared with the test data from a NASA Centaur test vehicle which included both direct and submerged injection with draining of propellants. The numerical model developed with GFSSP has been validated against two sets of experimental data and has been shown to predict both propellant subcooling and helium consumption to within 30% in most cases. The test data used for the model validation were taken in 1-g, but the mass diffusion model was developed to be applied in both 1-g and micro-g environments.

Cryogenics↗
NASA NTRS1971

Comparison of several methods for estimating low speed stability derivatives

Methods presented in five different publications have been used to estimate the low-speed stability derivatives of two unpowered airplane configurations. One configuration had unswept lifting surfaces, the other configuration was the D-558-II swept-wing research airplane. The results of the computations were compared with each other, with existing wind-tunnel data, and with flight-test data for the D-558-II configuration to assess the relative merits of the methods for estimating derivatives. The results of the study indicated that, in general, for low subsonic speeds, no one text appeared consistently better for estimating all derivatives.

Fletcher, H. S.↗
NASA NTRS1974

Reaction control system plume flow field interaction effects on the Space Shuttle orbiter

This paper presents an analysis of data obtained from wind tunnel tests of the aerodynamic interference induced by the reaction control system jets on Space Shuttle orbiter configurations. The test data was obtained using cold gas simulation techniques with nozzles scaled to match jet exit momentum ratio as the primary parameter at Mach numbers from 2.5 to 10. Significant induced effects have been found that degrade the performance of the pitch and roll reaction controls and that induce cross-coupling effects for yaw reaction control. Analysis of the induced data shows good correlation with jet exit momentum ratio.

Rausch, J. R.↗
NASA NTRS1975

Design and testing of an energy flywheel for an Integrated Power/Attitude Control System /IPACS/

This paper summarizes the design of a prototype flywheel energy storage assembly developed to evaluate the spacecraft Integrated Power and Attitude Control System (IPACS) concept. In the IPACS application, the flywheel assembly is used for kinetic electrical energy storage as well as conventional angular momentum control. The kinetic energy storage function dictates high rotational speeds which require new approaches to the design of the major components: rotors, motor-generators, bearing systems, and electronics. The paper includes a general description of a NASA-contracted prototype assembly, a discussion of major component design characteristics, and the presentation of preliminary test results as compared with analytical predictions. The test data were obtained from preliminary tests of the NASA prototype assembly as well as from a Rockwell prototype test unit.

Notti, J. E.↗