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At least 523 records · Page 29

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NASA NTRSDate not supplied

A Comparison of Model Predictive Control Architectures for Application to Electrified Aircraft Propulsion Systems

As electrified aircraft propulsion (EAP) systems continue to mature, more sophisticated hardware and software are being developed to balance operations among electric machines and gas-turbine engines. In hybrid-electric propulsion systems, the increased complexity resulting from integrating turbine-engine shafts with electric machines necessitates control methodologies to account for various physical domains. Ideal controllers for hybrid-electric engines manage systems, subsystems, and their interactions in a coordinated fashion, able to account for safety and performance goals while being computationally efficient. In a previous work, linear model predictive control (MPC) schemes were implemented in centralized and distributed frameworks on a nonlinear turbofan engine model as a proof of concept. However, these schemes were not evaluated for computational complexity, prompting further study. The research presented here develops hierarchical MPC schemes to reduce the computational burden of the previous MPC schemes. A two-tier framework is implemented, where a slower sampling MPC controls electric machines and determines fan-speed tracking goals for a faster sampling controller, which is either a MPC or a proportional-integral (PI) controller. The proposed designs are compared to the centralized MPC investigated previously, and performance is measured via fan speed tracking error, energy storage state-of-charge, and computation time. Results reveal that the hierarchical MPC scheme employing a lower-level PI controller improves computation time while maintaining comparable tracking and state-of-charge regulation to the centralized scheme.

model predictive control↗

NASA NTRSDate not supplied

A Comparison of Model Predictive Control Architectures for Application to Electrified Aircraft Propulsion Systems

model predictive control↗

NASA NTRS1987

A piloted simulator evaluation of a ground-based 4D descent advisor algorithm

A ground-based, four-dimensional (4D) descent-advisor algorithm is under development at NASA Ames Research Center. The algorithm combines detailed aerodynamic, propulsive, and atmospheric models with an efficient numerical integration scheme to generate 4D descent advisories. This paper investigates the ability of the 4D descent advisor algorithm to provide adequate control of arrival time for aircraft not equipped with on-board 4D guidance systems. A piloted simulation was conducted to determine the precision with which the descent advisor could predict the 4D trajectories of typical straight-in descents flown by airline pilots under different wind conditions. The effects of errors in the estimation of wind and initial aircraft weight were also studied. A description of the descent advisor as well as the results of the simulation studies are presented.

Green, Steven M.↗

NASA NTRS1973

An evaluation of a constrained test method for obtaining free body responses

A method for obtaining free body responses from dynamic tests on a constrained structure is investigated for practical feasibility. The method is based on the principle that a constrained structure can be considered to be a free body acted upon by multiple forces which include the forces of constraint. By measuring these forces and by exciting the structure so as to develop linearly independent sets of forces, the response of the free body to one force at a time can be computed. Techniques for producing these independent forces are discussed. The development of the theory, computer simulations of tests of representative aerospace vehicles (including experimental error), and a description and listing of the computer programs developed are included. The procedure appears to be a practical method for obtaining in-flight characteristics of such vehicles.

Berman, A.↗

NASA NTRS1980

Evaluation of the procedure for separating barley from other spring small grains

The success of the Transition Year procedure to separate and label barley and the other small grains was assessed. It was decided that developers of the procedure would carry out the exercise in order to prevent compounding procedural problems with implementation problems. The evaluation proceeded by labeling the sping small grains first. The accuracy of this labeling was, on the average, somewhat better than that in the Transition Year operations. Other departures from the original procedure included a regionalization of the labeling process, the use of trend analysis, and the removal of time constraints from the actual processing. Segment selection, ground truth derivation, and data available for each segment in the analysis are discussed. Labeling accuracy is examined for North Dakota, South Dakota, Minnesota, and Montana as well as for the entire four-state area. Errors are characterized.

Magness, E. R.↗

NASA NTRS2010

Simulation Studies for a Space-Based CO2 Lidar Mission

We report results of initial space mission simulation studies for a laser-based, atmospheric CO2 sounder, which are based on real-time carbon cycle process modelling and data analysis. The mission concept corresponds to the Active Sensing of CO2 Emissions over Nights, Days and Seasons (ASCENDS) recommended by the US National Academy of Sciences' Decadal Survey. As a pre-requisite for meaningful quantitative evaluation, we employ a CO2 model that has representative spatial and temporal gradients across a wide range of scales. In addition, a relatively complete description of the atmospheric and surface state is obtained from meteorological data assimilation and satellite measurements. We use radiative transfer calculations, an instrument model with representative errors and a simple retrieval approach to quantify errors in 'measured' CO2 distributions, which are a function of mission and instrument design specifications along with the atmospheric/surface state. Uncertainty estimates based on the current instrument design point indicate that a CO2 laser sounder can provide data consistent with ASCENDS requirements and will significantly enhance our ability to address carbon cycle science questions. Test of a dawn/dusk orbit deployment, however, shows that diurnal differences in CO2 column abundance, indicative of plant photosynthesis and respiration fluxes, will be difficult to detect

Kawa, S. R.↗

NASA NTRS2021

Chapter 5: Extravehicular Activity Metabolic Rate Model: Metabolic Rate Estimated from Heart Rate

In-flight monitoring of crew metabolic rates during extravehicular activity (EVA) provides crucial information in mitigating injury. The purpose of this study was to investigate the relationship of crewmember heart rate (HR) and metabolic rate (MR) during EVA operations to develop a predictive linear model. HR and MR data was collected from 132 EVAs from Shuttle and International Space Station (ISS) missions. MR was collected every 2-min from portable life support system delta oxygen decay, while HR was collected every 20-sec via electrocardiogram. HR was down sampled to every 2-min to match MR during EVA for evaluation. Further, a new metric was observed from direct relations between metabolic rate with HR over EVA time (MR/HR) measured as a BTU/beat. A range of BTU/beat was collected as a conversion scale between MR and HR at different EVA workloads categorized by increased MR. Both HR and MR values were observed to decrease through the duration of EVA. Similarly, HR and MR slopes decreased at start of EVA compared to end of EVA. MR/HR values were used to predict MR from HR over the entire duration of EVA with root mean square error less than 200 BTU/Hr. Additionally, MR was predicted based on HR values during EVA via a calculated simple linear regression. A regression equation was found for each EVA drawing relations between HR and MR (F (2923.84) and P<0.0001) with an R(sup 2) value of 0.402. Individual crew regressions improved prediction and R(sup 2) to greater than 0.82. Two models are presented to determine metabolic rate from heart rate during EVA. Results draw correlations for heart rate and metabolic rate fluctuations during EVA for individualized crew predictions during future operations. The linear models correlate to Apollo prediction data during historic EVAs.

Metabolic rate predictions↗

NASA NTRSDate not supplied

Assessing Utility of Different Orbits for a Lunar PNT Constellation

"As the Artemis program establishes a long-term presence on the lunar surface, lunar surface users will need an accurate source of Position, Navigation, and Timing (PNT). Under the LunaNet framework, NASA has proposed the Lunar Navigation System (LNS), a constellation of satellites in lunar orbit which will broadcast LunaNet’s Augmented Forward Signal (AFS) [1] to the lunar surface. LNS will have the objective of providing user position accuracies of 10 m and timing accuracies of 10 microseconds on the lunar surface and up to 200 km above the surface. Several classes of orbits are possibilities for the LNS constellation, including circular orbits, eccentric orbits, and various families of 3-body orbits. Each of these orbit classes have both advantages and disadvantages in their utility as PNT constellations. In this study we examine a wide variety of potential LNS constellations and evaluate their performance against several metrics, including: a. Dilution of Precision (DOP) performance over the lunar service volume and the South Pole region, during both the constellation buildup and after the constellation is completed. b. Number of satellites required to achieve required DOP performance. c. Relative dynamics of LNS satellites with respect to surface users. d. Signal in space error (SISE) performance, assuming orbit determination that includes the Global Positioning System (GPS), crosslinks, and monitor sites on the surface of the moon. e. Constellation insertion, station keeping, and disposal costs. f. Specific Concept of Operations (CONOPS) and engineering challenges associated with establishing and operating the constellations. (E.g., frequent station keeping, variable signal strength, divergent CONOPS for different planes of the constellation.) The system’s performance is considered both independently and in combination with other proposed systems, such as NASA’s Lunar Communication Relay and Navigation System (LCRNS) and ESA’s Moonlight constellation. The study concludes that a 3-plane Walker constellation at 6 lunar radii (slightly higher than GPS’s 4.2 earth radii from a geometry perspective, but significantly closer in an absolute sense) is a good candidate for the LNS constellation, providing the user with good SISE and DOP performance, while not requiring excessive station keeping or complex CONOPS. However, other viable concepts exist and could be chosen if early South Pole coverage is a driving factor in the system design."

navigation↗

NASA NTRS1982

Variations in propagation delay times for line ten (TV) based time transfers

Variation in the propagation delay for a 30 km TV (Line Ten) radio link was evaluated for a series of 30 independent measurements. Time marks from TV Channel 5 WTTG in Washington, D.C. were simultaneously measured at the Johns Hopkins University Applied Physics Laboratory and at the United States Naval Observatory against each stations' local cesium standard clocks. Differences in the stations' cesium clocks were determined by portable cesium clock transfers. Thirty independent timing determinations were made. The root mean square deviation in the propagation delay calculated from the timing determinations was 11 ns. The variations seen in the propagation delays are believed to be caused by environmental factors and by errors in the portable clock timing measurements. In correlating the propagation delay variations with local weather conditions, only a moderate dependence on air temperature and absolute humidity was found.

Chiu, M. C.↗

NASA NTRS1982

Establishment of a rotor model basis

Radial-dimension computations in the RSRA's blade-element model are modified for both the acquisition of extensive baseline data and for real-time simulation use. The baseline data, which are for the evaluation of model changes, use very small increments and are of high quality. The modifications to the real-time simulation model are for accuracy improvement, especially when a minimal number of blade segments is required for real-time synchronization. An accurate technique for handling tip loss in discrete blade models is developed. The mathematical consistency and convergence properties of summation algorithms for blade forces and moments are examined and generalized integration coefficients are applied to equal-annuli midpoint spacing. Rotor conditions identified as 'constrained' and 'balanced' are used and the propagation of error is analyzed.

Mcfarland, R. E.↗

NASA NTRS1986

The implementation and use of Ada on distributed systems with high reliability requirements

The general inadequacy of Ada for programming systems that must survive processor loss was shown. A solution to the problem was proposed in which there are no syntatic changes to Ada. The approach was evaluated using a full-scale, realistic application. The application used was the Advanced Transport Operating System (ATOPS), an experimental computer control system developed for a modified Boeing 737 aircraft. The ATOPS system is a full authority, real-time avionics system providing a large variety of advanced features. Methods of building fault tolerance into concurrent systems were explored. A set of criteria by which the proposed method will be judged was examined. Extensive interaction with personnel from Computer Sciences Corporation and NASA Langley occurred to determine the requirements of the ATOPS software. Backward error recovery in concurrent systems was assessed.

Knight, J. C.↗

NASA NTRS1988

A simulator investigation of the use of digital data link for pilot/ATC communications in a single pilot operation

Studies have shown that radio communications between pilots and air traffic control contribute to high pilot workload and are subject to various errors. These errors result from congestion on the voice radio channel, and missed and misunderstood messages. The use of digital data link has been proposed as a means of reducing this workload and error rate. A critical factor, however, in determining the potential benefit of data link will be the interface between future data link systems and the operator of those systems, both in the air and on the ground. The purpose of this effort was to evaluate the pilot interface with various levels of data link capability, in simulated general aviation, single-pilot instrument flight rule operations. Results show that the data link reduced demands on pilots' short-term memory, reduced the number of communication transmissions, and permitted the pilots to more easily allocate time to critical cockpit tasks while receiving air traffic control messages. The pilots who participated unanimously indicated a preference for data link communications over voice-only communications. There were, however, situations in which the pilot preferred the use of voice communications, and the ability for pilots to delay processing the data link messages, during high workload events, caused delays in the acknowledgement of messages to air traffic control.

Hinton, David A.↗

NASA NTRS1983

Transient responses of phosphoric acid fuel cell power plant system

An analytical and computerized study of the steady state and transient response of a phosphoric acid fuel cell (PAFC) system was completed. Parametric studies and sensitivity analyses of the PAFC system's operation were accomplished. Four non-linear dynamic models of the fuel cell stack, reformer, shift converters, and heat exchangers were developed based on nonhomogeneous non-linear partial differential equations, which include the material, component, energy balance, and electrochemical kinetic features. Due to a lack of experimental data for the dynamic response of the components only the steady state results were compared with data from other sources, indicating reasonably good agreement. A steady state simulation of the entire system was developed using, nonlinear ordinary differential equations. The finite difference method and trial-and-error procedures were used to obtain a solution. Using the model, a PAFC system, that was developed under NASA Grant, NCC3-17, was improved through the optimization of the heat exchanger network. Three types of cooling configurations for cell plates were evaluated to obtain the best current density and temperature distributions. The steady state solutions were used as the initial conditions in the dynamic model. The transient response of a simplified PAFC system, which included all of the major components, subjected to a load change was obtained. Due to the length of the computation time for the transient response calculations, analysis on a real-time computer was not possible. A simulation of the real-time calculations was developed on a batch type computer. The transient response characteristics are needed for the optimization of the design and control of the whole PAFC system. All of the models, procedures and simulations were programmed in Fortran and run on IBM 370 computers at Cleveland State University and the NASA Lewis Research Center.

Lu, Cheng-Yi↗

NASA NTRS1996

SeaWiFs Technical Report Series. Volume 34: The Third SeaWiFS Intercalibration Round-Robin Experiment (SIRREX-3), 19-30 September 1994

This report presents results of the third Sea-viewing Wide Field-of-view Sensor (SeaWiFS) Intercalibration Round- Robin Experiment (SIRREX-3), which was held at the San Diego State University (SDSU) Center for Hydro-Optics and Remote Sensing (CHORS) on 19-30 September 1994. Spectral irradiances of FEL lamps belonging to each participant were intercompared by reference to the National Institute of Standards and Technology (NIST) scale of spectral irradiance using secondary standard lamps F268, F269, and F182, with a Type A uncertainty between 1.1-1.5%. This level of uncertainty was achieved despite difficulties with lamp F269. The average spectral irradiances of FEL lamps, compared in both SIRREX-2 and SIRREX-3, differed between the two experiments by 1.5%, which probably indicates that the values assigned to the secondary standard lamp at the time of SIRREX-2 were in error. With two exceptions, spectral radiance values of integrating sphere sources were measured during SIRREX-3 with uncertainties in temporal stability of less than 0.3% and absolute uncertainties of 1.5-2.0%. This is a significant improvement over similar intercomparisons in SIRREX- I and SIRREX-2. Plaque reflectances were intercompared with an uncertainty of about 1-2%, but the absolute uncertainty is undefined. Although this is an improvement over results of previous SIRREXS, the sources and magnitude of uncertainty associated with transfers of spectral radiance using plaques requires further evaluation in future experiments.

Hooker, Stanford B.↗

NASA NTRS1995

Miniature Telerobots in Space Applications

Ground controlled telerobots can be used to reduce astronaut workload while retaining much of the human capabilities of planning, execution, and error recovery for specific tasks. Miniature robots can be used for delicate and time consuming tasks such as biological experiment servicing without incurring the significant mass and power penalties associated with larger robot systems. However, questions remain regarding the technical and economic effectiveness of such mini-telerobotic systems. This paper address some of these open issues and the details of two projects which will provide some of the needed answers. The Microtrex project is a joint University of Washington/NASA project which plans on flying a miniature robot as a Space Shuttle experiment to evaluate the effects of microgravity on ground-controlled manipulation while subject to variable time-delay communications. A related project involving the University of Washington and Boeing Defense and Space will evaluate the effectiveness f using a minirobot to service biological experiments in a space station experiment 'glove-box' rack mock-up, again while subject to realistic communications constraints.

Venema, S. C.↗

NASA NTRS1998

Calculations of multiple scattering-induced errors in the GLAS mission

The Geoscience Lidar Altimeter System (GLAS) is a laser altimeter designed to measure temporal changes in the topography and mass balance of the Earth's ice sheets. GLAS is scheduled to be launched as part of the Earth Observing System (EOS) in 2001. Due to the large pulse width of GLAS and the slope (and roughness) of the ice sheets, the mean elevation of the laser's surface spot will be estimated from the centroid of the return pulse. While the accuracy of individual altimetry measurements is expected to be 15 cm, a cross-over technique that averages the elevation differences at selected points on the ice sheets will allow GLAS to detect mean ice elevation changes as small as 2 cm per year. One factor that may degrade the proposed accuracy of the altimeter measurements is the effect of multiple scattering by thin clouds and aerosols over the ice sheets. In the return pulse, some photons from the lidar are slightly deflected by cloud particles but still return to the instrument detector. Since these photons travel a longer path than photons that pass directly to and from the surface, the mean travel time of the pulse is lengthened and the centroid of the return pulse is shifted toward a later time . This study intends to determine the importance of this source of altimetry error in the GLAS measurements. Two methods will be used to estimate path delays in the GLAS lidar for a range of cloud conditions. An analytic expression of a doubly scattered return signal (Eloranta, 1972) will be compared to Monte Carlo simulations that estimate path delays by cloud, aerosol and molecular scattering. The results from both methods will be discussed in relationship to current knowledge of Arctic cloud climatology, and the impact of multiple scattering on GLAS altimeter measurements will be evaluated.

Duda, David P.↗

NASA NTRS2001

Localization of needle tip with color doppler during pericardiocentesis: In vitro validation and initial clinical application

This study evaluates a new device that uses color Doppler ultrasonography to enable real-time image guidance of the aspirating needle, which has not been possible until now. The ColorMark device (EchoCath Inc, Princeton, NJ) induces high-frequency, low-amplitude vibrations in the needle to enable localization with color Doppler. We studied this technique in 25 consecutive patients undergoing pericardiocentesis, and in vitro, in a urethane phantom with which the accuracy of color Doppler localization of the needle tip was compared with that obtained by direct measurement. Tip localization was excellent in vitro; errors axial to the ultrasound beam (velocity Doppler -0.13 +/- 0.90 mm, power Doppler -0.05 +/- 1.7 mm) were less than lateral errors (velocity -0.36 +/- 1.8 mm, power -0.02 +/- 2.8 mm). In 18 of 25 patients, the needle was identified and guided into the pericardial space with the ColorMark technique, and it allowed successful, uncomplicated drainage of fluid. Initial failures were the result of incorrect settings on the echocardiographic machine and inappropriate combinations of the needle puncture site and imaging window. This study demonstrates a novel color Doppler technique that is highly accurate at localizing a needle tip. The technique is feasible for guiding pericardiocentesis. Further clinical validation of this technique is required.

NASA Discipline Cardiopulmonary↗

NASA NTRS2015

The Ocean Colour Climate Change Initiative: I. A Methodology for Assessing Atmospheric Correction Processors Based on In-Situ Measurements

The Ocean Colour Climate Change Initiative intends to provide a long-term time series of ocean colour data and investigate the detectable climate impact. A reliable and stable atmospheric correction procedure is the basis for ocean colour products of the necessary high quality. In order to guarantee an objective selection from a set of four atmospheric correction processors, the common validation strategy of comparisons between in-situ and satellite derived water leaving reflectance spectra, is extended by a ranking system. In principle, the statistical parameters such as root mean square error, bias, etc. and measures of goodness of fit, are transformed into relative scores, which evaluate the relationship of quality dependent on the algorithms under study. The sensitivity of these scores to the selected database has been assessed by a bootstrapping exercise, which allows identification of the uncertainty in the scoring results. Although the presented methodology is intended to be used in an algorithm selection process, this paper focusses on the scope of the methodology rather than the properties of the individual processors.

Climate Change↗