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At least 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Knowledge based imaging for terrain analysis

A planetary rover will have various vision based requirements for navigation, terrain characterization, and geological sample analysis. In this paper we describe a knowledge-based controller and sensor development system for terrain analysis. The sensor system consists of a laser ranger and a CCD camera. The controller, under the input of high-level commands, performs such functions as multisensor data gathering, data quality monitoring, and automatic extraction of sample images meeting various criteria. In addition to large scale terrain analysis, the system's ability to extract useful geological information from rock samples is illustrated. Image and data compression strategies are also discussed in light of the requirements of earth bound investigators.

Holben, Rick↗
NASA NTRS1988

A unified process for systems identification based on performance assessment

Many modern spacecraft are complex multi-body dynamic systems where the bodies are connected by several active control systems for pointing and isolation. Mission requirements indicate that many structural modes and possibly some nonlinear effects will require characterization. Thus, even characterization at the subsystem level will become more difficult than usual. System level characterization difficulties will be compounded by the fact that only limited ground testing will be possible on the full up system, and flight testing will be restricted by an extremely limited measurements set. The object of the present discussion is the application of matrix majorant theory to the problem of assessing dynamic system performance when knowledge of the system is uncertain. We show how majorants provide an effective tool to relate required performance output to system identification test quality in terms of residual uncertainty in input-output relations, parameter values, nonlinearities, and interactions. The underlying machinery consists of the block-norm matrix which is a nonnegative matrix each of whose elements is the norm of a block of a suitably partitioned matrix. A matrix which bounds the block-norm matrix in the sense of nonnegative matrices, i.e., element by element is known as a majorant.

Hyland, C.↗
NASA NTRSDate not supplied

Runway Configuration Management with Offline Reinforcement Learning

Runway configuration management (RCM) is a challenging task, and it affects the efficiency of the National Airspace System (NAS) and airport surface operations significantly. Each airport, depending on the geometry, capacity, local climate patterns, etc. has multiple configurations for the runway usage for arriving and departing flights. Many factors such as the incoming/outgoing traffic load, wind direction and speed, convective weather, cloud ceiling and other environmental factors might affect the choice of a runway configuration at any point in time. However, other factors such as safety measures and regulations, noise abatement, capacity of each configuration, and preference of the air traffic controllers (ATCs) can also play a significant role in selecting the configuration. A sub-optimal selection of the runway configuration, or delay in making configuration changes might result in significant increase in taxi times for aircraft on the surface of the airport, fuel and energy use of the aircraft, and maintenance costs. It can also lead to safety concerns, such as an aircraft performing one or more go-arounds before being able to land. All these factors make RCM an extremely important and challenging decision-making process for the ATCs. The current state of practice sets the runway configuration by the ATCs based on relevant information available at the time including weather, traffic, noise abatement, safety bounds, etc. This makes the decision-making process subjective based on the accuracy of the available information and the bias in human decision making. Unfortunately, this approach yields poor results (e.g., significant delays) if the predicted outcomes are uncertain and their relative impact is not well understood. This is especially evident when the uncertainty increases the size of possible predicted outcomes (combinatorial explosion in possible scenarios) that cannot be handled by human reasoning. On the other hand, an automated approach based on machine intelligence can make use of historical data and search through all (or significant amount of) possible scenarios under uncertainty and make well-informed decisions.

Milad Memarzadeh↗
NASA NTRS1975

Propellers of Minimum Induced Loss, and Water Tunnel Tests of Such a Propeller

The fundamental vortex theory for a single rotation propeller with a finite number of blades is reviewed. The theory leads to the specification of a radial distribution of bound circulation on each blade for minimum induced loss, analogous to the elliptic spanwise distribution of bound circulation on a wing for minimum induced drag. A propeller designed in accord with this theory has been tested in a water tunnel where it exhibited high efficiency in spite of localized cavitating flow. A knowledge of the flow field for an optimum propeller is of value to the airframe designer seeking to maximize the performance of the airplane-propeller combination.

Larrabee, E. E.↗
NASA NTRS1995

Calibration and postlaunch performance of the Meteor 3/TOMS instrument

Prelaunch and postlaunch calibration results for the Meteor 3/total ozone mapping spectrometer (TOMS) instrument are presented here. Ozone amounts are retrieved from measurements of Earth albedo in the 312- to 380-nm range. The accuracy of albedo measurements is primarily tied to knowledge of the reflective properties of diffusers used in the calibrations and to the instrument's wavelength selection. These and other important prelaunch calibrations are presented. Their estimated accuracies are within the bounds necessary to determine column ozone to better than 1%. However, postlaunch validation results indicate some prelaunch calibration uncertainties may be larger than originally estimated. Instrument calibrations have been maintained postlaunch to within a corresponding 1% error in retrieved ozone. Onboard calibrations, including wavelength monitoring and a three-diffuser solar measurement system, are described and specific results are presented. Other issues, such as the effects of orbital precession on calibration and recent chopper wheel malfunctions, are also discussed.

Jaross, G.↗
NASA NTRS1989

Global models: Robot sensing, control, and sensory-motor skills

Robotics research has begun to address the modeling and implementation of a wide variety of unstructured tasks. Examples include automated navigation, platform servicing, custom fabrication and repair, deployment and recovery, and science exploration. Such tasks are poorly described at onset; the workspace layout is partially unfamiliar, and the task control sequence is only qualitatively characterized. The robot must model the workspace, plan detailed physical actions from qualitative goals, and adapt its instantaneous control regimes to unpredicted events. Developing robust representations and computational approaches for these sensing, planning, and control functions is a major challenge. The underlying domain constraints are very general, and seem to offer little guidance for well-bounded approximation of object shape and motion, manipulation postures and trajectories, and the like. This generalized modeling problem is discussed, with an emphasis on the role of sensing. It is also discussed that unstructured tasks often have, in fact, a high degree of underlying physical symmetry, and such implicit knowledge should be drawn on to model task performance strategies in a methodological fashion. A group-theoretic decomposition of the workspace organization, task goals, and their admissible interactions are proposed. This group-mechanical approach to task representation helps to clarify the functional interplay of perception and control, in essence, describing what perception is specifically for, versus how it is generically modeled. One also gains insight how perception might logically evolve in response to needs of more complex motor skills. It is discussed why, of the many solutions that are often mathematically admissible to a given sensory motor-coordination problem, one may be preferred over others.

Schenker, Paul S.↗
NASA NTRS1990

Control/structure interaction study of a Space Station Freedom first flight concept during reboost

In the current design, the Space Station first-flight configuration will be assembled in a LEO and reboosted to a higher altitude such that the orbital decay due to atmospheric drag forces will lower the spacecraft to the proper altitude at the appropriate time to rendezvous with the next-assembly flight of the orbiter. The reboost maneuver will be performed by firing the on/off reaction control system jets to increase the forward velocity. This paper describes the design of a basic orbital reboost maneuver based on a burn-coast-burn scenario and a closed-loop attitude control system which will control the firing sequences of the jets to maintain the spacecraft attitude within required bounds. The design is then used to investigate the infuence of the elastic component response on the reboost jet firing logic.

Lim, Tae W.↗
NASA NTRS2006

Using the Climbing Drum Peel (CDP) Test to Obtain a G(sub IC) value for Core/Facesheet Bonds

A method of measuring the Mode I fracture toughness of core/facesheet bonds in sandwich Structures is desired, particularly with the widespread use of models that need this data as input. This study examined if a critical strain energy release rate, G(sub IC), can be obtained from the climbing drum peel (CDP) test. The CDP test is relatively simple to perform and does not rely on measuring small crack lengths such as required by the double cantilever beam (DCB) test. Simple energy methods were used to calculate G(sub IC) from CDP test data on composite facesheets bonded to a honeycomb core. Facesheet thicknesses from 2 to 5 plies were tested to examine the upper and lower bounds on facesheet thickness requirements. Results from the study suggest that the CDP test, with certain provisions, can be used to find the GIG value of a core/facesheet bond.

Nettles, A. T.↗
NASA NTRS2010

Stereoscopic Machine-Vision System Using Projected Circles

A machine-vision system capable of detecting obstacles large enough to damage or trap a robotic vehicle is undergoing development. The system includes (1) a pattern generator that projects concentric circles of laser light forward onto the terrain, (2) a stereoscopic pair of cameras that are aimed forward to acquire images of the circles, (3) a frame grabber and digitizer for acquiring image data from the cameras, and (4) a single-board computer that processes the data. The system is being developed as a prototype of machine- vision systems to enable robotic vehicles ( rovers ) on remote planets to avoid craters, large rocks, and other terrain features that could capture or damage the vehicles. Potential terrestrial applications of systems like this one could include terrain mapping, collision avoidance, navigation of robotic vehicles, mining, and robotic rescue. This system is based partly on the same principles as those of a prior stereoscopic machine-vision system in which the cameras acquire images of a single stripe of laser light that is swept forward across the terrain. However, this system is designed to afford improvements over some of the undesirable features of the prior system, including the need for a pan-and-tilt mechanism to aim the laser to generate the swept stripe, ambiguities in interpretation of the single-stripe image, the time needed to sweep the stripe across the terrain and process the data from many images acquired during that time, and difficulty of calibration because of the narrowness of the stripe. In this system, the pattern generator does not contain any moving parts and need not be mounted on a pan-and-tilt mechanism: the pattern of concentric circles is projected steadily in the forward direction. The system calibrates itself by use of data acquired during projection of the concentric-circle pattern onto a known target representing flat ground. The calibration- target image data are stored in the computer memory for use as a template in processing terrain images. During operation on terrain, the images acquired by the left and right cameras are analyzed. The analysis includes (1) computation of the horizontal and vertical dimensions and the aspect ratios of rectangles that bound the circle images and (2) comparison of these aspect ratios with those of the template. Coordinates of distortions of the circles are used to identify and locate objects. If the analysis leads to identification of an object of significant size, then stereoscopicvision algorithms are used to estimate the distance to the object. The time taken in performing this analysis on a single pair of images acquired by the left and right cameras in this system is a fraction of the time taken in processing the many pairs of images acquired in a sweep of the laser stripe across the field of view in the prior system. The results of the analysis include data on sizes and shapes of, and distances and directions to, objects. Coordinates of objects are updated as the vehicle moves so that intelligent decisions regarding speed and direction can be made. The results of the analysis are utilized in a computational decision-making process that generates obstacle-avoidance data and feeds those data to the control system of the robotic vehicle.

Mackey, Jeffrey R.↗
NASA NTRS1978

High-flying Mini-Sniffer RPV - Mars bound

The Mini-Sniffer is a small unmanned survey aircraft developed by NASA to conduct turbulence and atmospheric pollution measurements from ground level to an altitude of 90,000 ft. Carrying a 25-lb air sampling apparatus, the Mini-Sniffer typically cruises for one hour at 70,000 ft before being remotely piloted back to earth. A hydrazine monopropellant engine powers the craft, while a PCM telemetering system and a radar transponder provide control functions. Development of a high-performance low-Reynolds-number airfoil could make the research craft suitable for a low-altitude terrain-following mission on Mars.

Reed, R. D.↗
NASA NTRS2010

Experimental Charging Behavior of Orion UltraFlex Array Designs

The present ground based investigations give the first definitive look describing the charging behavior of Orion UltraFlex arrays in both the Low Earth Orbital (LEO) and geosynchronous (GEO) environments. Note the LEO charging environment also applies to the International Space Station (ISS). The GEO charging environment includes the bounding case for all lunar mission environments. The UltraFlex photovoltaic array technology is targeted to become the sole power system for life support and on-orbit power for the manned Orion Crew Exploration Vehicle (CEV). The purpose of the experimental tests is to gain an understanding of the complex charging behavior to answer some of the basic performance and survivability issues to ascertain if a single UltraFlex array design will be able to cope with the projected worst case LEO and GEO charging environments. Stage 1 LEO plasma testing revealed that all four arrays successfully passed arc threshold bias tests down to -240 V. Stage 2 GEO electron gun charging tests revealed that only the front side area of indium tin oxide coated array designs successfully passed the arc frequency tests

Golofaro, Joel T.↗
NASA NTRS2011

Multiple Damage Progression Paths in Model-Based Prognostics

Model-based prognostics approaches employ domain knowledge about a system, its components, and how they fail through the use of physics-based models. Component wear is driven by several different degradation phenomena, each resulting in their own damage progression path, overlapping to contribute to the overall degradation of the component. We develop a model-based prognostics methodology using particle filters, in which the problem of characterizing multiple damage progression paths is cast as a joint state-parameter estimation problem. The estimate is represented as a probability distribution, allowing the prediction of end of life and remaining useful life within a probabilistic framework that supports uncertainty management. We also develop a novel variance control mechanism that maintains an uncertainty bound around the hidden parameters to limit the amount of estimation uncertainty and, consequently, reduce prediction uncertainty. We construct a detailed physics-based model of a centrifugal pump, to which we apply our model-based prognostics algorithms. We illustrate the operation of the prognostic solution with a number of simulation-based experiments and demonstrate the performance of the chosen approach when multiple damage mechanisms are active

Daigle, Matthew↗
NASA NTRS2017

Characterization of Volatiles Loss from Soil Samples at Lunar Environments

Resource Prospector Integrated Thermal Vacuum Test Program A series of ground based dirty thermal vacuum tests are being conducted to better understand the subsurface sampling operations for RP Volatiles loss during sampling operations Hardware performance Sample removal and transfer Concept of operationsInstrumentation5 test campaigns over 5 years have been conducted with RP hardware with advancing hardware designs and additional RP subsystems Volatiles sampling 4 years Using flight-forward regolith sampling hardware, empirically determine volatile retention at lunar-relevant conditions Use data to improve theoretical predictions Determine driving variables for retention Bound water loss potential to define measurement uncertainties. The main goal of this talk is to introduce you to our approach to characterizing volatiles loss for RP. Introduce the facility and its capabilities Overview of the RP hardware used in integrated testing (most recent iteration) Summarize the test variables used thus farReview a sample of the results.

In Situ Resource Utilization↗
NASA NTRS2020

Demonstration of Deployment Accuracy of the Starshade Inner Disk Subsystem

We present experimental results that demonstrate the required in-plane deployment accuracy of the starshade Inner Disk Subsystem (IDS). This effort was to address Milestone 7C of the Starshade Technology Activity S5, which requires that the in-plane deployment accuracy of the petal interfaces on the IDS be within +/-300um. A full-scale 10m-diameter IDS prototype was constructed. This prototype comprised a medium-fidelity perimeter truss, medium-fidelity spokes, and a low-fidelity optical shield (OS). The testbed also included gravity compensation systems and a laser tracker metrology system. The post-processed measurement uncertainties of the laser tracker were less than 30um at the 3 sigma level. Design, engineering and fabrication of these components was done by JPL, Tendeg, and Roccor. Testing was performed at the Tendeg facility in Louisville, Colorado. The IDS prototype was deployed 22 times and the locations of petal interfaces on the IDS were measured after each deployment. Based on this data, tolerance intervals were calculated that would contain 99.73% of future deployment accuracy errors with 90% confidence. These tolerance intervals are conservative estimates for 3 sigma bounds. The tolerance intervals for the three pertinent error components were found to be within the required allocations, with at least 19% margin.

Turse, Dana↗
NASA NTRS1977

Fundamental electronic mechanisms limiting the performance of solar cells

Attention is focused on distortion in the energy band, and carrier recombination and generation rates (lifetimes), as the two dominant mechanisms. Spatial dependences associated with these two mechanisms, in the direction normal to the surface illuminated by the sun and in the direction tangential to that surface, are also emphasized as crucial factors in governing the efficiency of solar cells. Electronic parameters for the set of differential equations characterizing transport, recombination, and generation of carriers, and interband and band-bound transition rates, are studied.

Lindholm, F. A.↗
NASA NTRS1991

Performance Analysis of Garbage Collection and Dynamic Reordering in a Lisp System

Generation based garbage collection and dynamic reordering of objects are two techniques for improving the efficiency of memory management in Lisp and similar dynamic language systems. An analysis of the effect of generation configuration is presented, focusing on the effect of a number of generations and generation capabilities. Analytic timing and survival models are used to represent garbage collection runtime and to derive structural results on its behavior. The survival model provides bounds on the age of objects surviving a garbage collection at a particular level. Empirical results show that execution time is most sensitive to the capacity of the youngest generation. A technique called scanning for transport statistics, for evaluating the effectiveness of reordering independent of main memory size, is presented.

Llames, Rene Lim↗
NASA NTRS1993

A numerical study of confined turbulent jets

A numerical investigation is reported of turbulent incompressible jets confined in two ducts, one cylindrical and the other conical with a 5 degree divergence. In each case, three Craya-Curtet numbers are considered which correspond, respectively, to flow situations with no moderate and strong recirculation. Turbulence closure is achieved by using the k-epsilon model and a recently proposed realizable Reynolds stress algebraic equation model that relates the Reynolds stresses explicitly to the quadratic terms of the mean velocity gradients and ensures the positiveness of each component of the turbulent kinetic energy. Calculations are carried out with a finite-volume procedure using boundary-fitted curvilinear coordinates. A second-order accurate, bounded convection scheme and sufficiently fine grids are used to prevent the solutions from being contaminated by numerical diffusion. The calculated results are compared extensively with the available experimental data. It is shown that the numerical methods presented are capable of capturing the essential flow features observed in the experiments and that the realizable Reynolds stress algebraic equation model performs much better than the k-epsilon model for this class of flows of great practical importance.

Zhu, J.↗
NASA NTRS2010

The First Detection of (O IV) from an Ultraluminous X-Ray Source with Spitzer. 2. Evidence for High Luminosity in Holmberg II ULX

This is the second of two papers examining Spitzer Infrared Spectrograph observations of the ultraluminous X-ray source (ULX) in Holmberg II. Here, we perform detailed photoionization modeling of the infrared lines. Our analysis suggests that the luminosity and morphology of the [Oiv] 25.89 micronmeters emission line is consistent with photoionization by the soft X-ray and far ultraviolet (FUV) radiation from the accretion disk of the binary system and inconsistent with narrow beaming. We show that the emission nebula is matter bounded both in the line-of-sight direction and to the east, and probably radiation-bounded to the west. A bolometric luminosity in excess of 10(exp 40) erg s(exp -1) would be needed to produce the measured [O iv] flux. We use modeling and previously published studies to conclude that shocks likely contribute very little, if at all,to the high-ionization line fluxes observed in the Holmberg II ULX. Additionally, we find that the spectral type of the companion star has a surprisingly strong effect on the predicted strength of the [O iv] emission. This finding could explain the origin of [O iv] in some starburst systems containing black hole binaries.

GALAXIES↗