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At least 1,225 records · Page 68

Evaluating human performance modeling for system assessment: Promise and problems

The development and evaluation of computational human performance models is examined. An intention is to develop models which can be used to interact with system prototypes and simulations to perform system assessment. Currently LR is working on a set of models emulating cognitive, psychomotor, auditory, and visual activity for multiple operator positions of a command and control simulation system. These models, developed in conjunction with BBN Systems and Technologies, function within the simulation environment and allow for both unmanned system assessment and manned (human-in-loop) assessment of system interface and team interactions. These are relatively generic models with built-in flexibility which allows modification of some model parameters. These models have great potential for improving the efficiency and effectiveness of system design, test, and evaluation. However, the extent of the practical utility of these models is unclear. Initial verification efforts comparing model performance within the simulation to actual human operators on a similar, independent simulation have been performed and current efforts are directed at comparing human and model performance within the same simulation environment.

Patterson, Robert W.↗

Low and high velocity impact response of thick hybrid composites

The effects of low and high velocity impact on thick hybrid composites (THC's) were experimentally compared. Test Beams consisted of CFRP skins which were bonded onto an interleaved syntactic foam core and cured at 177 C (350 F). The impactor tip for both cases was a 16 mm (0.625 inch) steel hemisphere. In spite of the order of magnitude difference in velocity ranges and impactor weights, similar relationships between impact energy, damage size, and residual strength were found. The dependence of the skin compressive strength on damage size agree well with analytical open hole models for composite laminates and may enable the prediction of ultimate performance for the damaged composite, based on visual inspection.

Hiel, Clement↗

A study of the absorption-line spectra of six high-redshift quasi-stellar objects

High-resolution spectrograms of six QSOs with apparent visual magnitudes of 17.0 to 18.5 and redshifts greater than 2 are studied for absorption lines. Accurate wavelengths are measured for all the absorption lines that could be detected, attempts are made to identify redshift systems, and the redshifts in each object are examined. Analysis of the absorption-line spectra shows that: (1) a large number of redshifts covering a wide range of values are present in five of the QSOs; (2) about two-thirds of the absorption lines remain unidentified, cannot be of Galactic origin, and are not associated with existing redshift systems; (3) many comparatively small absorption redshifts exist which, if they are due to intervening galaxies, must be produced by very large halos; and (4) in one QSO there is a possible redshift system containing five lines with an absorption redshift that is significantly greater than the emission redshift.

Roberts, D. H.↗

The occultation of SAO 78505 by Jupiter

On 13 December 1989, Jupiter occulted a star with visual magnitude 8.7 and an estimated K magnitude of 7. We observed the event from Kitt Peak, Arizona, using a 64 x 64 infrared camera at a wavelength of 2.16 microns. The resulting data on refractive defocusing of the stellar signal give information on the temperature of the jovian atmosphere at pressures approximately 2 to 10 microbar, at near-equatorial latitudes. These are the first new stellar-occulation data for the high jovian atmosphere since the widely observed occulation of beta Sco A and C in 1971. Because of improvements in instrumental capability, our data are comparable to the best beta Sco A data though the star is six magnitudes fainter. We derive a mean atmospheric temperature of 176 +/- 12 K on a level surface corresponding to an equatorial radius of 71,880 km and a pressure of 1.8 microbar at a jovi- centric latitude of 8 deg. This result complements the beta Sco results by providing improved precision at low jovicentric latitudes where the fainter star beta Sco C was used in 1971.

Hubbard, W. B.↗

Deciphering the Precision of Stereo IKONOS Canopy Height Models for U.S. Forests with G-LiHT Airborne LiDAR

Few studies have evaluated the precision of IKONOS stereo data for measuring forest canopy height. The high cost of airborne light detection and ranging (LiDAR) data collection for large area studies and the present lack of a spaceborne instrument lead to the need to explore other low cost options. The US Government currently has access to a large archive of commercial high-resolution imagery, which could be quite valuable to forest structure studies. At 1 m resolution, we here compared canopy height models (CHMs) and height data derived from Goddard's airborne LiDAR Hyper-spectral and Thermal Imager (G-LiHT) with three types of IKONOS stereo derived digital surface models (DSMs) that estimate CHMs by subtracting National Elevation Data (NED) digital terrain models (DTMs). We found the following in three different forested regions of the US after excluding heterogeneous and disturbed forest samples: (1) G-LiHT DTMs were highly correlated with NED DTMs with R (sup 2) greater than 0.98 and root mean square errors (RMSEs) less than 2.96 m; (2) when using one visually identifiable ground control point (GCP) from NED, G-LiHT DSMs and IKONOS DSMs had R (sup 2) greater than 0.84 and RMSEs of 2.7 to 4.1 m; and (3) one GCP CHMs for two study sites had R (sup 2) greater than 0.7 and RMSEs of 2.6 to 3 m where data were collected less than four years apart. Our results suggest that IKONOS stereo data are a useful LiDAR alternative where high-quality DTMs are available.

IKONOS↗

The effect of spurious angular accelerations on tracking in dynamic simulation

A laboratory study was conducted to investigate the effect of spurious simulator yaw motions on a pilot's control performance. A second objective was to compare the efficiency of static and dynamic simulator tracking in previously unexamined vehicle dynamics. Twelve airline pilots served as subjects in a moving-base flight simulator under congruent-motion, spurious-motion, and no-motion conditions. The results indicated a significant increase in the amount of error with increasing levels of spurious motion during the initially administered series of trials. The influence of spurious motion, however, was absent in a second series of trials. The data suggest that the pilots learned to compensate in their performance for the spurious inputs. It was also found that congruent visual and rotational cueing produced superior performance to that of tracking with visual information alone.

Beck, L. J.↗

HST photometry of the trapezium cluster

We have obtained images of 11 fields in the Trapezium cluster with the Planetary Camera (PC) of the Hubble Space Telescope (HST) in order to extend Herbig & Terndrup's (1986) study of this prototype, dense embedded cluster to fainter magnitudes than is possible from the ground. Using these images, we have identified 319 stars within an area of approximately 12 sq arc min corresponding roughly to a volume of approximately 0.065 cu pc assuming the cluster is approximately spherically symmetric. Our completeness limits for star identification in V-band and I-band images are V approximately = 20 and I(sub c) approximately = 19 respectively, corresponding to a mass limit of approximately 0.15 solar mass if the faintest stars have the same average A(sub v) as that estimated for the brighter stars in the cluster. We have compared the V versus V-I color-magnitude diagram derived from the HST photometry to new theoretical isochrones. Star formation in the Trapezium appears to be remarkably coeval, with greater than or = 80% of the stars having inferred ages less than 1 Myr. Over the somewhat limited mass range of the observations, there is no evidence for 'bimodal' star formation-the high- and low-mass stars appear to have the same ages. The sharp cores of the HST images and the small angular size of the PC pixels has allowed us to identify 35 new visual binaries in the cluster with separations from approximately 0.06 arc sec (approximately 26 AU) to approximately 1.0 arc sec (approximately 440 AU). For the range of binary separations that we are sensitive to, the observed binary frequency for the Trapezium is essentially identical to that estimated for field low-mass stars by Duquennoy & Mayor (1991). The most straightfoward inference from this result is that binaries in this separation are unlikely to be formed by a tidal capture process. We have also identified three stars which have associated compact nebulosity visible in the HST images. One of these star + nebulosity cases was previously identified by O'Dell, Wen, & Hu (1993)-these objects appear to form a class of objects whose circumstellar matter is being 'lit up', most likely by Theta(sup 1) Ori C, enabling the gas to be observable at both optical and radio wavelengths (Felli et al. 1993a, b). We provide a brief summary of the optical properties of the other radio sources which appear in our PC images.

Prosser, Charles F.↗

Motion Cueing Algorithm Development: Piloted Performance Testing of the Cueing Algorithms

The relative effectiveness in simulating aircraft maneuvers with both current and newly developed motion cueing algorithms was assessed with an eleven-subject piloted performance evaluation conducted on the NASA Langley Visual Motion Simulator (VMS). In addition to the current NASA adaptive algorithm, two new cueing algorithms were evaluated: the optimal algorithm and the nonlinear algorithm. The test maneuvers included a straight-in approach with a rotating wind vector, an offset approach with severe turbulence and an on/off lateral gust that occurs as the aircraft approaches the runway threshold, and a takeoff both with and without engine failure after liftoff. The maneuvers were executed with each cueing algorithm with added visual display delay conditions ranging from zero to 200 msec. Two methods, the quasi-objective NASA Task Load Index (TLX), and power spectral density analysis of pilot control, were used to assess pilot workload. Piloted performance parameters for the approach maneuvers, the vertical velocity upon touchdown and the runway touchdown position, were also analyzed but did not show any noticeable difference among the cueing algorithms. TLX analysis reveals, in most cases, less workload and variation among pilots with the nonlinear algorithm. Control input analysis shows pilot-induced oscillations on a straight-in approach were less prevalent compared to the optimal algorithm. The augmented turbulence cues increased workload on an offset approach that the pilots deemed more realistic compared to the NASA adaptive algorithm. The takeoff with engine failure showed the least roll activity for the nonlinear algorithm, with the least rudder pedal activity for the optimal algorithm.

Houck, Jacob A.↗

Famine Early Warning Systems Network (FEWS NET) Land Data Assimilation System (LDAS) and Other Assimilated Hydrological Data at NASA GES DISC

The NASA Goddard Earth Sciences Data and Information Services Center (GES DISC) provides science support for several data sets relevant to agriculture and food security, including the Famine Early Warning Systems Network (FEWS NET) Land Data Assimilation System (LDAS), or FLDAS data set. The GES DISC is one of twelve NASA Earth Observing System (EOS) data centers that process, archive, document, and distribute data from Earth science missions and related projects. The GES DISC hosts a wide range of remote sensing and model data, and provides reliable and robust data access and other services to users worldwide. Beyond data archive and access, the GES DISC offers many services to visualize and analyze the data. This presentation provides a summary of the hydrological data available at the GES DISC, along with an overview of related data services. Specifically, the FLDAS data set has been adapted to work with domains, data streams, and monitoring and forecast requirements associated with food security assessment in data-sparse, developing country settings. The FLDAS global monthly data have a 0.1 x 0.1 degree spatial resolution covering the period from January 1982 to present. Global FLDAS monthly anomaly and monthly climatology data are also available at the GES DISC to evaluate how current conditions compare to averages over the FLDAS 35-year period. Several case studies using the FLDAS soil moisture, evapotranspiration, rainfall, runoff, and surface temperature data will be presented.

Loeser, Carlee↗

Automated anomaly detection for Orbiter High Temperature Reusable Surface Insulation

The description, analysis, and experimental results of a method for identifying possible defects on High Temperature Reusable Surface Insulation (HRSI) of the Orbiter Thermal Protection System (TPS) is presented. Currently, a visual postflight inspection of Orbiter TPS is conducted to detect and classify defects as part of the Orbiter maintenance flow. The objective of the method is to automate the detection of defects by identifying anomalies between preflight and postflight images of TPS components. The initial version is intended to detect and label gross (greater than 0.1 inches in the smallest dimension) anomalies on HRSI components for subsequent classification by a human inspector. The approach is a modified Golden Template technique where the preflight image of a tile serves as the template against which the postflight image of the tile is compared. Candidate anomalies are selected as a result of the comparison and processed to identify true anomalies. The processing methods are developed and discussed, and the results of testing on actual and simulated tile images are presented. Solutions to the problems of brightness and spatial normalization, timely execution, and minimization of false positives are also discussed.

Cooper, Eric G.↗

Full-scale S-76 rotor performance and loads at low speeds in the NASA Ames 80- by 120-Foot Wind Tunnel

A full-scale helicopter rotor test was conducted in the NASA Ames 80- by 120-Foot Wind Tunnel with a four-bladed S-76 rotor system. Rotor performance and loads data were obtained over a wide range of rotor shaft angles-of-attack and thrust conditions at tunnel speeds ranging from 0 to 100 kt. The primary objectives of this test were (1) to acquire forward flight rotor performance and loads data for comparison with analytical results; (2) to acquire S-76 forward flight rotor performance data in the 80- by 120-Foot Wind Tunnel to compare with existing full-scale 40- by 80-Foot Wind Tunnel test data that were acquired in 1977; (3) to evaluate the acoustic capability of the 80- by 120- Foot Wind Tunnel for acquiring blade vortex interaction (BVI) noise in the low speed range and compare BVI noise with in-flight test data; and (4) to evaluate the capability of the 80- by 120-Foot Wind Tunnel test section as a hover facility. The secondary objectives were (1) to evaluate rotor inflow and wake effects (variations in tunnel speed, shaft angle, and thrust condition) on wind tunnel test section wall and floor pressures; (2) to establish the criteria for the definition of flow breakdown (condition where wall corrections are no longer valid) for this size rotor and wind tunnel cross-sectional area; and (3) to evaluate the wide-field shadowgraph technique for visualizing full-scale rotor wakes. This data base of rotor performance and loads can be used for analytical and experimental comparison studies for full-scale, four-bladed, fully articulated rotor systems. Rotor performance and structural loads data are presented in this report.

Shinoda, Patrick M.↗

Benefit of "Push-pull" Locomotion for Planetary Rover Mobility

As NASAs exploration missions on planetary terrains become more aggressive, a focus on alternative modes of locomotion for rovers is necessary. In addition to climbing steep slopes, the terrain in these extreme environments is often unknown and can be extremely hard to traverse, increasing the likelihood of a vehicle or robot becoming damaged or immobilized. The conventional driving mode in which all wheels are either driven or free-rolling is very efficient on flat hard ground, but does not always provide enough traction to propel the vehicle through soft or steep terrain. This paper presents an alternative mode of travel and investigates the fundamental differences between these locomotion modes. The methods of push-pull locomotion discussed can be used with articulated wheeled vehicles and are identified as walking or inchinginch-worming. In both cases, the braked non-rolling wheels provide increased thrust. An in-depth study of how soil reacts under a rolling wheel vs. a braked wheel was performed by visually observing the motion of particles beneath the surface. This novel technique consists of driving or dragging a wheel in a soil bin against a transparent wall while high resolution, high-rate photographs are taken. Optical flow software was then used to determine shearing patterns in the soil. Different failure modes were observed for the rolling and braked wheel cases. A quantitative comparison of inching vs. conventional driving was also performed on a full-scale vehicle through a series of drawbar pull tests in the Lunar terrain strength simulant, GRC-1. The effect of tire stiffness was also compared; typically compliant tires provide better traction when driving in soft soil, however its been observed that rigid wheels may provide better thrust when non-rolling. Initial tests indicate up to a possible 40 increase in pull force capability at high slip when inching vs. rolling.

robotics↗

Evaluation of 2 1-D cloud models for the analysis of VAS soundings

Evaluation of the satellite Visual Infrared Spin Scan Radiometer Atmospheric Sounder (VISSR) has begun to document several of its critical shortcomings as far as numerical cloud models are concerned: excessive smoothing of thermal inversions; imprecise measurement of boundary layer moisture; and tendency to exaggerate atmospheric stability. The sensitivity of 1-D cloud models to their required inputs is stressed with special attention to those parameters obtained from atmospheric soundings taken by the VAS or rawinsonde. In addition to performing model experiments using temperature and moisture profiles having the general characteristics of VAS soundings, standard input sensitivity tests were made and 1-D model performance was compared with observations and the results of a 2-D model experiment using AVE/VAS data (Atmospheric Variability Experiment). Although very encouraging, the results are not sufficient to make any specific conclusions. In general, the VAS soundings are likely to be inadequate to provide the cloud base (and subcloud layer) information needed for inputs to current cumulus models. Above cloud base, the tendency to exaggerate the stability of the atmosphere requires solution before meaningful model experiments are run.

Emmitt, G. D.↗

Application of the wide-field shadowgraph technique to helicopters in forward flight

A test was conducted to examine the feasibility of using the wide-field shadowgraph method for visualizing the wake of a small-scale helicopter rotor in forward flight. A wide range of test conditions were examined, including thrust and forward speed variations. Shadowgraphs from the side and top of the rotor were obtained. The visibility of the tip vortices using the shadowgraph method was documented for advance ratios up to 0.175. It was demonstrated that shadowgraphs of the rotor wake in forward flight can be used to obtain qualitative and quantitative information about wake geometry, wake/body interactions, and blade/vortex interactions. Video cameras were used for the first time to record the shadowgraphs. These provided several advantages compared to still cameras and greatly enhanced the capabilities of the shadowgraph method.

Light, Jeffrey S.↗

Characterization of Mesoscale Convective Systems by Means of Composite Radar Reflectivity Data

A mesoscale convective system (MCS) is broadly defined as a cloud and precipitation system of mesoscale dimensions (often too large for most aircraft to circumnavigate) with deep-convective activity concentrated in at least part of the MCS, or present during part of its evolution. A large areal fraction of MCSs is stratiform in nature, yet estimates from MCSs over the Great Plains, the Southeast, and tropical waters indicate that at least half of the precipitation is of convective origin. The presence of localized convection is important, because within convective towers cloud particles and hydrometeors are carried upward towards the cloud top. Ice crystals then move over more stratiform regions, either laterally, or through in situ settling over decaying and spreading convection. These ice crystals then grow to precipitation-size particles in mid- to upper tropospheric mesoscale updrafts. The convective portion of a MCS is often a more or less continuous line of thunderstorms, and may be either short-lived or long-lived. Geerts (1997) presents a preliminary climatology of MCSs in the southeastern USA, using just one year of composite digital radar reflectivity data. In this study MCSs are identified and characterized by means of visual inspection of animated images. A total of 398 MCSs were identified. In the warm season MCSs were found to be about twice as frequent as in the cold season. The average lifetime and maximum length of MCSs are 9 hours, and 350 km, respectively, but some MCSs are much larger and more persistent. In the summer months small and short-lived MCSs are relatively more common, whereas in winter larger and longer-lived systems occur more frequently. MCSs occur more commonly in the afternoon, in phase with thunderstorm activity, but the amplitude of the diurnal cycle is small compared to that of observed thunderstorms. It is estimated that in the Southeast more than half of all precipitation and severe weather results from MCSs.

Geerts, Bart↗

Double Cantilever Beam and End Notched Flexure Fracture Toughness Testing of Two Composite Materials

Two different unidirectional composite materials were provided by NASA Langley Research Center and tested by the Composite Materials Research Group within the Department of Mechanical Engineering at the University of Wyoming. Double cantilever beam and end notched flexure tests were performed to measure the mode I (crack opening) and mode II (sliding or shear) interlaminar fracture toughness of the two materials. The two composites consisted of IM7 carbon fiber combined with either RP46 resin toughened with special formulation of LaRC IA resin, known as JJS1356; or PES chain extended thermoplastic resin known as JJS1361. Double Cantilever Beam Specimen Configuration and Test Methods As received from NASA, the test specimens were nominally 0.5 inch wide, 6 inches long, and 0.2 inch thick. A 1 inch long Kapton insert at the midplane of one end of the specimen (placed during laminate fabrication) facilitated crack initiation and extension. It was noted that the specimens provided were smaller than the nominal 1.5 inch wide, 9.0 inch long configuration specified. Similarly, the Kapton inserts were of greater length than those in the present specimens. Hence, the data below should not be compared directly to those generated with the referenced methods. No preconditioning was performed on the specimens prior to testing. In general, the methodology was used for the present work. Crack opening loads were introduced to the specimens via piano hinges attached to the main specimen faces at a single end of each specimen. Hinges were bolted to the specimens using the technique presented. The cracks were extended a small distance from the end of the Kapton insert prior to testing. Just before precracking, the sides of the specimens were coated with water-soluble typewriter correction fluid to aid in crack visualization. Scribe marks were then made in the coating at half-inch intervals.

Kessler, Jeff A.↗

Timescale Correlation between Marine Atmospheric Exposure and Accelerated Corrosion Testing - Part 2

Evaluation of metals to predict service life of metal-based structures in corrosive environments has long relied on atmospheric exposure test sites. Traditional accelerated corrosion testing relies on mimicking the exposure conditions, often incorporating salt spray and ultraviolet (UV) radiation, and exposing the metal to continuous or cyclic conditions similar to those of the corrosive environment. Their reliability to correlate to atmospheric exposure test results is often a concern when determining the timescale to which the accelerated tests can be related. Accelerated corrosion testing has yet to be universally accepted as a useful tool in predicting the long-term service life of a metal, despite its ability to rapidly induce corrosion. Although visual and mass loss methods of evaluating corrosion are the standard, and their use is crucial, a method that correlates timescales from accelerated testing to atmospheric exposure would be very valuable. This paper presents work that began with the characterization of the atmospheric environment at the Kennedy Space Center (KSC) Beachside Corrosion Test Site. The chemical changes that occur on low carbon steel, during atmospheric and accelerated corrosion conditions, were investigated using surface chemistry analytical methods. The corrosion rates and behaviors of panels subjected to long-term and accelerated corrosion conditions, involving neutral salt fog and alternating seawater spray, were compared to identify possible timescale correlations between accelerated and long-term corrosion performance. The results, as well as preliminary findings on the correlation investigation, are presented.

Montgomery, Eliza L.↗

Evaluating the Subjective Straight Ahead Before and After Spaceflight

Introduction. This joint European Space Agency/NASA pre- and post-flight study investigates the influence of exposure to microgravity on the subjective straight ahead (SSA) in crewmembers returning from long-duration expeditions to the International Space Station (ISS). The SSA is a measure of the internal representation of body orientation and to be influenced by stimulation of sensory systems involved in postural control. The use of a vibrotactile sensory aid to correct the representation of body tilted relative to gravity is also tested as a countermeasure. This study addresses the sensorimotor research gap to "determine the changes in sensorimotor function over the course of a mission and during recovery after landing." Research Plans. The ISS study will involve eight crewmembers who will participate in three pre-flight sessions (between 120 and 60 days before launch) and then three post-flight sessions on R plus 0/1 day, R plus 4 days, and R plus 8 days. Sixteen control subjects were also tested during three sessions to evaluate the effects of repeated testing and to establish normative values. The experimental protocol includes measurements of gaze and arm movements during the following tasks: (1) Near & Far Fixation: The subject is asked to look at actual targets in the true straight-ahead direction or to imagine these targets in the dark. Targets are located at near distance (arm's length) and far distance (beyond 2 meters). This task is successively performed with the subject's body aligned with the gravitational vertical, and with the subject's body tilted in pitch relative to the gravitational vertical using a tilt chair. Measures are then compared with and without a vibrotactile sensory aid that indicates how far one has tilted relative to the vertical; (2) Eye and Arm Movements: The subject is asked to look and point in the SSA direction in darkness and then make horizontal and vertical eye or arm movements, relative to Earth coordinates (allocentric) and to the subject's head/body reference (egocentric). This task is successively performed with the subject's body aligned with the gravitational vertical, and with subject's body tilted in roll using a tilt chair; (3) Linear Vestibulo-Ocular Reflex: The subject is asked to fixate actual visual targets at near and far distances in the true straight-ahead direction, and to evaluate the distance of these targets. The subject is asked to continue fixating the same imagined targets in darkness while he/she is passively accelerated up and down on a spring-loaded vertical linear accelerator. Results. In the control subject population, the perceived tilt angles, translations, and distances were remarkably close to the actual values. The pointing tasks indicated that the orientation of arm saccades was influenced by both the gravitational vertical and the body idiotropic vector. Repeating the testing did not reveal any significant changes. Preliminary results obtained in three crewmembers before and after flight will also be presented. Applications. A change in an individual's egocentric reference might have negative consequences on evaluating the direction of an approaching object or on the accuracy of reaching movements or locomotion. Consequently, investigating how microgravity affects the target location will have theoretical, operational, and even clinical implications for future space exploration missions. The use of vibrotactile feedback as a sensorimotor countermeasure is applicable to balance therapy applications for patients with vestibular loss and the elderly to mitigate risks due to loss of spatial orientation.

Campbell, D. J.↗