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At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Optimal input design for aircraft instrumentation systematic error estimation

A new technique for designing optimal flight test inputs for accurate estimation of instrumentation systematic errors was developed and demonstrated. A simulation model of the F-18 High Angle of Attack Research Vehicle (HARV) aircraft was used to evaluate the effectiveness of the optimal input compared to input recorded during flight test. Instrumentation systematic error parameter estimates and their standard errors were compared. It was found that the optimal input design improved error parameter estimates and their accuracies for a fixed time input design. Pilot acceptability of the optimal input design was demonstrated using a six degree-of-freedom fixed base piloted simulation of the F-18 HARV. The technique described in this work provides a practical, optimal procedure for designing inputs for data compatibility experiments.

Morelli, Eugene A.↗
NASA NTRS2001

Use of TRMM Data to Test an Improved Parameterization of Stratiform Precipitation

By incorporating the TRMM satellite orbital information into the most recent geodesic version of the Colorado State University General Circulation Model (CSU GCM), we are able to fly a satellite in the GCM, and sample the simulated atmosphere in the same way as the TRMM sensors sample the real atmosphere. The TRMM sampling statistics of precipitation and radiative fluxes at annual, intra-seasonal, monthly-mean and composited diurnal time scales are evaluated by comparing the satellite-sampled against fully-sampled simulated atmospheres. This information provides a valuable guidance for efficient usage of TRMM data and future satellite mission planning. We have also evaluated the effects of TRMM sampling errors on the inferred tropical-mean hydrologic cycle and radiative fluxes. We have found that there are strong spurious oscillations associated with the TRMM orbital geometry, with periods of 23 days and 3-4 months, in tropical-mean daily and monthly precipitation. Caution must therefore be used when applying TRMM observations of tropical-mean precipitation to interpret climate variations at intraseasonal and interannual scales.

Randall, David A.↗
NASA NTRS2004

Evaluation and Application of Satellite-Based Latent Heating Profile Estimation Methods

In recent years, methods for estimating atmospheric latent heating vertical structure from both passive and active microwave remote sensing have matured to the point where quantitative evaluation of these methods is the next logical step. Two approaches for heating algorithm evaluation are proposed: First, application of heating algorithms to synthetic data, based upon cloud-resolving model simulations, can be used to test the internal consistency of heating estimates in the absence of systematic errors in physical assumptions. Second, comparisons of satellite-retrieved vertical heating structures to independent ground-based estimates, such as rawinsonde-derived analyses of heating, provide an additional test. The two approaches are complementary, since systematic errors in heating indicated by the second approach may be confirmed by the first. A passive microwave and combined passive/active microwave heating retrieval algorithm are evaluated using the described approaches. In general, the passive microwave algorithm heating profile estimates are subject to biases due to the limited vertical heating structure information contained in the passive microwave observations. These biases may be partly overcome by including more environment-specific a priori information into the algorithm s database of candidate solution profiles. The combined passive/active microwave algorithm utilizes the much higher-resolution vertical structure information provided by spaceborne radar data to produce less biased estimates; however, the global spatio-temporal sampling by spaceborne radar is limited. In the present study, the passive/active microwave algorithm is used to construct a more physically-consistent and environment-specific set of candidate solution profiles for the passive microwave algorithm and to help evaluate errors in the passive algorithm s heating estimates. Although satellite estimates of latent heating are based upon instantaneous, footprint- scale data, suppression of random errors requires averaging to at least half-degree resolution. Analysis of mesoscale and larger space-time scale phenomena based upon passive and passive/active microwave heating estimates from TRMM, SSMI, and AMSR data will be presented at the conference.

Olson, William S.↗
NASA NTRS2006

Stochastic Evolutionary Algorithms for Planning Robot Paths

A computer program implements stochastic evolutionary algorithms for planning and optimizing collision-free paths for robots and their jointed limbs. Stochastic evolutionary algorithms can be made to produce acceptably close approximations to exact, optimal solutions for path-planning problems while often demanding much less computation than do exhaustive-search and deterministic inverse-kinematics algorithms that have been used previously for this purpose. Hence, the present software is better suited for application aboard robots having limited computing capabilities (see figure). The stochastic aspect lies in the use of simulated annealing to (1) prevent trapping of an optimization algorithm in local minima of an energy-like error measure by which the fitness of a trial solution is evaluated while (2) ensuring that the entire multidimensional configuration and parameter space of the path-planning problem is sampled efficiently with respect to both robot joint angles and computation time. Simulated annealing is an established technique for avoiding local minima in multidimensional optimization problems, but has not, until now, been applied to planning collision-free robot paths by use of low-power computers.

Fink, Wolfgang↗
NASA NTRS2011

Terminal - Tactical Separation Assured Flight Environment (T-TSafe)

The Tactical Separation Assured Flight Environment (TSAFE) has been previously tested as a conflict detection and resolution tool in the en-route phase of flight. Fast time simulations of a terminal version of this tool called Terminal TSAFE (T-TSAFE) have shown promise over the current conflict detection tools. It has shown to have fewer false alerts (as low as 2 per hour) and better prediction to conflict time than Conflict Alert. The tool will be tested in the simulated terminal area of Los Angeles International Airport, in a Human-in-the-loop experiment to identify controller procedures and information requirements. The simulation will include comparisons of T-TSAFE with NASA's version of Conflict Alert. Also, some other variables such as altitude entry by the controller, which improve T-TSAFE's predictions for conflict detection, will be tested. T-TSAFE integrates features of current conflict detection tools such as Automated Terminal Proximity Alert used to alleviate compression errors in the final approach phase. Based on fast-time simulation analysis, the anticipated benefits of T-TSAFE over Conflict Alert include reduced false/missed alerts and increased time to predicted loss of separation. Other metrics that will be used to evaluate the tool's impact on the controller include controller intervention, workload, and situation awareness.

Verma, Savita Arora↗
NASA NTRS1977

One-way Doppler extractor

This paper presents a feasibility analysis, tradeoffs, and implementation for a one-way Doppler extractor system. A Doppler error analysis is discussed which shows that quantization error is a primary source of Doppler measurement error. Several competing extraction techniques are compared, and a 'Vernier' technique is presented which obtains high Doppler resolution with low-speed logic. Parameter tradeoffs and sensitivities for this Vernier technique are discussed, leading to a hardware design configuration. Also presented is a performance evaluation of the resulting breadboard model that verifies the theoretical performance predictions. The breadboard model contains the circuitry to interface with an S-band transponder, to extract the Doppler and time-interval counts, to compute navigational parameters by means of a microprocessor, and to display the results. Performance tests have verified that the breadboard is capable of extracting Doppler, on an S-band signal, to an accuracy of better than 0.02 hertz for a one-second averaging period. This corresponds to a range rate error of no more than 3 millimeters per second.

Nossen, E. J.↗
NASA NTRS2014

Human-Robot Interaction Directed Research Project

Human-robot interaction (HRI) is a discipline investigating the factors affecting the interactions between humans and robots. It is important to evaluate how the design of interfaces and command modalities affect the human's ability to perform tasks accurately, efficiently, and effectively when working with a robot. By understanding the effects of interface design on human performance, workload, and situation awareness, interfaces can be developed to appropriately support the human in performing tasks with minimal errors and with appropriate interaction time and effort. Thus, the results of research on human-robot interfaces have direct implications for the design of robotic systems. This DRP concentrates on three areas associated with interfaces and command modalities in HRI which are applicable to NASA robot systems: 1) Video Overlays, 2) Camera Views, and 3) Command Modalities. The first study focused on video overlays that investigated how Augmented Reality (AR) symbology can be added to the human-robot interface to improve teleoperation performance. Three types of AR symbology were explored in this study, command guidance (CG), situation guidance (SG), and both (SCG). CG symbology gives operators explicit instructions on what commands to input, whereas SG symbology gives operators implicit cues so that operators can infer the input commands. The combination of CG and SG provided operators with explicit and implicit cues allowing the operator to choose which symbology to utilize. The objective of the study was to understand how AR symbology affects the human operator's ability to align a robot arm to a target using a flight stick and the ability to allocate attention between the symbology and external views of the world. The study evaluated the effects type of symbology (CG and SG) has on operator tasks performance and attention allocation during teleoperation of a robot arm. The second study expanded on the first study by evaluating the effects of the type of navigational guidance (CG and SG) on operator task performance and attention allocation during teleoperation of a robot arm through uplinked commands. Although this study complements the first study on navigational guidance with hand controllers, it is a separate investigation due to the distinction in intended operators (i.e., crewmembers versus ground-operators). A third study looked at superimposed and integrated overlays for teleoperation of a mobile robot using a hand controller. When AR is superimposed on the external world, it appears to be fixed onto the display and internal to the operators' workstation. Unlike superimposed overlays, integrated overlays often appear as three-dimensional objects and move as if part of the external world. Studies conducted in the aviation domain show that integrated overlays can improve situation awareness and reduce the amount of deviation from the optimal path. The purpose of the study was to investigate whether these results apply to HRI tasks, such as navigation with a mobile robot. HRP GAPS This HRI research contributes to closure of HRP gaps by providing information on how display and control characteristics - those related to guidance, feedback, and command modalities - affect operator performance. The overarching goals are to improve interface usability, reduce operator error, and develop candidate guidelines to design effective human-robot interfaces.

Sandor, Aniko↗
NASA NTRS2020

Improving Rain/No-Rain Detection Skill by Merging Precipitation Estimates from Different Sources

Rain/no-rain detection error is a key source of uncertainty in regional and global precipitation products that propagates into offline hydrological and land surface modeling simulations. Such detection error is difficult to evaluate and/or filter without access to high-quality reference precipitation datasets. For cases where such access is not available, this study proposes a novel approach for improved rain/no-rain detection. Based on categorical triple collocation (CTC) and a probabilistic framework, a weighted merging algorithm (CTC-M) is developed to combine noisy, but independent, precipitation products into an optimal binary rain/no-rain time series. Compared with commonly used approaches that directly apply the best parent product for rain/no-rain detection, the superiority of CTC-M is demonstrated analytically and numerically using spatially dense precipitation measurements over Europe. Our analysis also suggests that CTC-M is tolerant to a range of cross-correlated rain/no-rain detection errors and detection biases of the parent products. As a result, CTC-M will benefit global precipitation estimation by improving the representation of precipitation occurrence in gauge-based and multisource merged precipitation products.

Jianzhi Dong↗
NASA NTRS1984

Precise time transfer using MKIII VLBI technology

It is well known that Very Long Baseline Interferometry (VLBI) is capable of precise time synchronization at subnanosecond levels. This paper deals with a demonstration of clock synchronization using the MKIII VBLI system. The results are compared with clock synchronization by traveling cesium clocks and GPS. The comparison agrees within the errors of the portable clocks (+ 5 ns) and GPS(+ or - 30 ns) systems. The MKIII technology appears to be capable of clock synchronization at subnanosecond levels and appears to be very good benchmark system against which future time synchronization systems can be evaluated.

Johnston, K. J.↗
NASA NTRS1987

Measurement-based reliability/performability models

Measurement-based models based on real error-data collected on a multiprocessor system are described. Model development from the raw error-data to the estimation of cumulative reward is also described. A workload/reliability model is developed based on low-level error and resource usage data collected on an IBM 3081 system during its normal operation in order to evaluate the resource usage/error/recovery process in a large mainframe system. Thus, both normal and erroneous behavior of the system are modeled. The results provide an understanding of the different types of errors and recovery processes. The measured data show that the holding times in key operational and error states are not simple exponentials and that a semi-Markov process is necessary to model the system behavior. A sensitivity analysis is performed to investigate the significance of using a semi-Markov process, as opposed to a Markov process, to model the measured system.

Hsueh, Mei-Chen↗
NASA NTRS1990

Pipeline Time- And Transform-Domain Reed-Solomon Decoders

Modification of decoding algorithms leads to simplified conceptual designs for time- and transform-domain Reed-Soloman (RS) decoders suitable for implementation as very-large-scale integrated (VLSI) circuits. New conceptual decoders determine simultaneously errata-locator and errata-evaluator polynomials as part of simplified scheme for corrections of errors and erasures in RS codes. Highly suitable for implementation in both VLSI circuitry and in software on general-purpose computer.

Hsu, In-Shek↗
NASA NTRS1999

Five-Hole Flow Angle Probe Calibration for the NASA Glenn Icing Research Tunnel

A spring 1997 test section calibration program is scheduled for the NASA Glenn Research Center Icing Research Tunnel following the installation of new water injecting spray bars. A set of new five-hole flow angle pressure probes was fabricated to properly calibrate the test section for total pressure, static pressure, and flow angle. The probes have nine pressure ports: five total pressure ports on a hemispherical head and four static pressure ports located 14.7 diameters downstream of the head. The probes were calibrated in the NASA Glenn 3.5-in.-diameter free-jet calibration facility. After completing calibration data acquisition for two probes, two data prediction models were evaluated. Prediction errors from a linear discrete model proved to be no worse than those from a full third-order multiple regression model. The linear discrete model only required calibration data acquisition according to an abridged test matrix, thus saving considerable time and financial resources over the multiple regression model that required calibration data acquisition according to a more extensive test matrix. Uncertainties in calibration coefficients and predicted values of flow angle, total pressure, static pressure. Mach number. and velocity were examined. These uncertainties consider the instrumentation that will be available in the Icing Research Tunnel for future test section calibration testing.

Gonsalez, Jose C.↗
NASA NTRS2005

Contour Error Map Algorithm

The contour error map (CEM) algorithm and the software that implements the algorithm are means of quantifying correlations between sets of time-varying data that are binarized and registered on spatial grids. The present version of the software is intended for use in evaluating numerical weather forecasts against observational sea-breeze data. In cases in which observational data come from off-grid stations, it is necessary to preprocess the observational data to transform them into gridded data. First, the wind direction is gridded and binarized so that D(i,j;n) is the input to CEM based on forecast data and d(i,j;n) is the input to CEM based on gridded observational data. Here, i and j are spatial indices representing 1.25-km intervals along the west-to-east and south-to-north directions, respectively; and n is a time index representing 5-minute intervals. A binary value of D or d = 0 corresponds to an offshore wind, whereas a value of D or d = 1 corresponds to an onshore wind. CEM includes two notable subalgorithms: One identifies and verifies sea-breeze boundaries; the other, which can be invoked optionally, performs an image-erosion function for the purpose of attempting to eliminate river-breeze contributions in the wind fields.

Merceret, Francis↗
NASA NTRS2011

Simulations of Recovery of Time-Varying Gravity from DECIGO Pathfinder

We simulated time-varying Earth's gravity field recovered from DPF to evaluate an impact of DPF and future satellite gradiometry mission on earth science. From hydrological water movement data and orbit information, gravity gradients to be measured at altitude about ~500km were generated. Errors caused by atmospheric and oceanic variations and instrumental noise were added. Monthly gravity fields were estimated solving normal equations between spherical harmonic coefficients and simulated gravity gradient data. Simulation results show that DPF likely provides monthly hydrological water storage change with spatial scale between 400 and 1000km. Sensitivities to large scale estimates depends on long-term stability of gravity gradient measurement, and errors in short scale estimates are caused by instrumental noise and imperfections in atmospheric and ocean model. With acceleration noise level is lower than ~5 x 10(exp -14) [m/s2/sqrtHz] at frequency higher than 3mHz, water storage changes at limited small basins will be provided by DPF. To monitor continental scale hydrological water movement, noise level must be lower than ~5 x 10(exp -14) [m/s2/sqrtHz] at frequency higher than 1mHz.

Hasegawa, Takashi↗
NASA NTRS2012

Jason-1 and Jason-2 POD Using GPS

The Jason-2 satellite, launched in June 2008, is the latest follow-on to the successful Jason-1 altimetry satellite mission launched in December 7, 2001. Both, Jason-2 and Jason-1 are equipped with a GPS dual-frequency receiver, a laser retroreflector array, and a DORIS receiver for precise orbit determination (POD). A series of dynamic and reduced-dynamic Jason-2 orbits computed at NASA GSFC, based on GPS-only data and the std0905 standards, have been completed till cy74through cycle 74 using the IGS05 framework. These orbits, now publicly available, have been shown to agree radially at 1 cm RMS with the GSFC std0905 SLR/DORIS orbits and in comparison with orbits produced by JPL, ESA and CNES. In this paper, we describe the implementation of the IGS08 and repro1 framework for the Jason-2 and Jason-1 GPS POD processing with the NASA GSFC GEODYN software. . In our updated GPS POD, ambiguity fixing and updated time variable and static gravity fields. We also evaluate the implementation of non-tidal and degree-1 loading displacement as forward modeling to the tracking stations. Reduced-dynamic versus dynamic orbit differences are used to characterize the remaining force model errors and TRF instability. In particular, we assess their consistency radially and the stability of the altimeter satellite reference frame in the North/South direction as a proxy to assess the consistency of the reference frame.

Melachroinos, Stavros↗
NASA NTRS1998

Theoretical Accuracy for ESTL Bit Error Rate Tests

"Bit error rate" [BER] for the purposes of this paper is the fraction of binary bits which are inverted by passage through a communication system. BER can be measured for a block of sample bits by comparing a received block with the transmitted block and counting the erroneous bits. Bit Error Rate [BER] tests are the most common type of test used by the ESTL for evaluating system-level performance. The resolution of the test is obvious: the measurement cannot be resolved more finely than 1/N, the number of bits tested. The tolerance is not. This paper examines the measurement accuracy of the bit error rate test. It is intended that this information will be useful in analyzing data taken in the ESTL. This paper is divided into four sections and follows a logically ordered presentation, with results developed before they are evaluated. However, first-time readers will derive the greatest benefit from this paper by skipping the lengthy section devoted to analysis, and treating it as reference material. The analysis performed in this paper is based on a Probability Density Function [PDF] which is developed with greater detail in a past paper, Theoretical Accuracy for ESTL Probability of Acquisition Tests, EV4-98-609.

Lansdowne, Chatwin↗
NASA NTRS1997

Autonomous Navigation with Ground-to-Space Doppler Measurements Referenced to a Temperature-Compensated Crystal Oscillator

The National Aeronautics and Space Administration (NASA) Goddard Space Flight Center (GSFC) has spent several years developing operational Onboard Navigation Systems (ONS's) to provide real-time autonomous, high-accuracy navigation products for spacecraft using NASA's space and ground communication systems. The highly successful Tracking and Data Relay Satellite System (TDRSS) ONS (TONS) experiment on the Explorer Platform/Extreme Ultraviolet Explorer (EP/EUVE) spacecraft, launched June 7, 1992, flight-demonstrated the ONS for high-accuracy navigation using TDRSS forward- link communications services, In late 1994, the ground station ONS (GONS) experiment, using the same EP/EUVE flight hardware, flight-demonstrated the feasibility of high-accuracy autonomous navigation using ground station forward-link communication services, with an ultrastable oscillator (USO) as the frequency reference (1 part in 10(exp 10) over 24 hours). This paper provides a follow-on analysis of GONS performance to assess the navigation accuracy achievable if GONS uses the significantly less stable (5 parts in 10(exp 8) over 24 hours, compared with a specification of 1 part in 10(exp 6)) Temperature-Compensated Crystal Oscillator (TCXO), which is integral to the transponder, as a frequency reference rather than an external USO. The GONS TCXO experiment results from a 20-day period are used to project the expected performance of an operational system. The GONS processes Doppler data derived from nominally scheduled ground station forward-link communication services using a sequential estimation algorithm enhanced by a sophisticated process noise model to provide onboard orbit and frequency determination. To evaluate the navigation accuracies achievable if a TCXO were used, actual experiment data (which used the USO as the frequency reference) were corrupted with errors from real TDRSS one-way return tracking measurements taken from EP/EUVE's TCXO. Analysis of the GONS TCXO experiment performance indicates that real-time onboard position accuracies of better than 300 meters (1 sigma) are achievable with as few as two tracking contacts per day for the EP/EUVE 525-kilometer altitude, 28.5-degree inclination orbit, provided the TCXO is as stable as that in EP/EUVE's TDRSS transponder. GONS using a TCXO frequency reference provides a viable option for many upcoming spacecraft missions with moderate position accuracy requirements and an interest in reducing their operational costs with autonomous navigation.

Radomski, M. S.↗
NASA NTRS1989

Real-time closed-loop simulation and upset evaluation of control systems in harsh electromagnetic environments

Digital control systems for applications such as aircraft avionics and multibody systems must maintain adequate control integrity in adverse as well as nominal operating conditions. For example, control systems for advanced aircraft, and especially those with relaxed static stability, will be critical to flight and will, therefore, have very high reliability specifications which must be met regardless of operating conditions. In addition, multibody systems such as robotic manipulators performing critical functions must have control systems capable of robust performance in any operating environment in order to complete the assigned task reliably. Severe operating conditions for electronic control systems can result from electromagnetic disturbances caused by lightning, high energy radio frequency (HERF) transmitters, and nuclear electromagnetic pulses (NEMP). For this reason, techniques must be developed to evaluate the integrity of the control system in adverse operating environments. The most difficult and illusive perturbations to computer-based control systems that can be caused by an electromagnetic environment (EME) are functional error modes that involve no component damage. These error modes are collectively known as upset, can occur simultaneously in all of the channels of a redundant control system, and are software dependent. Upset studies performed to date have not addressed the assessment of fault tolerant systems and do not involve the evaluation of a control system operating in a closed-loop with the plant. A methodology for performing a real-time simulation of the closed-loop dynamics of a fault tolerant control system with a simulated plant operating in an electromagnetically harsh environment is presented. In particular, considerations for performing upset tests on the controller are discussed. Some of these considerations are the generation and coupling of analog signals representative of electromagnetic disturbances to a control system under test, analog data acquisition, and digital data acquisition from fault tolerant systems. In addition, a case study of an upset test methodology for a fault tolerant electromagnetic aircraft engine control system is presented.

Belcastro, Celeste M.↗