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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Recent developments in monolithic phase-locked semiconductor laser arrays

Coherent combination of the power of several semiconductor lasers fabricated on the same substrate has been the subject of an intense research effort in recent years, the main motivation being to obtain higher power levels than those available from a single laser in a stable radiation pattern. Best results reported so far include 2.6 watts CW emitted power and less than 1 deg far-field angle (in the array plane) in arrays where all the lasers are electrically connected in parallel. A different type of coherent array, where each element has a separate contact, has been recently demonstrated. While requiring the more complex two-level metallization technology, applying a separate contact to each laser provides an additional degree of freedom in the design and the operation of monolithic arrays. The separate contacts can be employed to tailor the near-field and far-field distributions and to compensate for device-to-device nonuniformities. Furthermore, the control of the currents of the array elements allows the performance of a variety of other functions, such as beam scanning, spectral mode control, wavelength tuning and control of the mutual coherence between array elements.

Katz, J.↗
NASA NTRS1992

Effects of orbital exposure on Halar during the LDEF mission

Thermomechanical Analysis (TMA), Differential Scanning Calorimetry (DSC), and Thermogravimetric Analysis (TGA) were performed on samples of Halar exposed on the LDEF Mission for 6 years in orbit and unexposed Halar control samples. Sections 10-100 microns thick were removed from the exposed surface down to a depth of 1,000 microns through the 3 mm thick samples. The TMA and DSC results, which arise from the entire slice and not just its surface, showed no differences between the LDEF and the control samples. TMA scans were run from ambient to 300 C; results were compared by a tabulation of the glass transition temperatures. DSC scans were run from ambient to 700 C; the enthalpy of melting was compared for the samples as a function of section depth with the sample. The TGA results, which arise from the surface of the sample initially, showed a sharp increase in the topmost 50 micron section (the exposed, discolored side) in the weight loss of 170 C in oxygen. This weight loss dropped to bulk values in the range of depth of 50-200 microns. The control sample showed only a slight increase in weight loss as the top surface was approached. The LDEF Halar sample appears to be mechanically undamaged, with a surface layer which oxidizes faster as a result of orbital exposure.

Brower, William E., Jr.↗
NASA NTRS1971

Antenna control system

The objective of the antenna control system is to utilize the analysis and software developed for the simulated 40 foot antenna system to produce a unified software package providing complete computer control of the 40 foot antenna. The control system comprises a position programmer, scan generator and a digital controller.

Source record↗
NASA NTRS2000

BOREAS TE-8 Aspen Bark Spectral Reflectance Data

The BOREAS TE-08 team collected in-lab spectral reflectance data for aspen bark and leaves from three sites within the BOREAS SSA from 24-May-1994 to 16-Jun-1994 (IFC 1), 19-Jul-1994 to 08-Aug-1994 (IFC 2), and 30-Aug-1994 to 19-Sep-1994 (IFC 3). One to nine trees from each site were sampled during the three IFCs. Each tree was sampled in five different locations for bark spectral properties: BS, US, BR, BT, and BO. Additionally, a limited number of LV were collected. Bark samples were removed from the stem of the tree and placed in ziplock bags for transport to UNH, where they were scanned with a spectroradiometer in a controlled environment. Each sample was scanned twice: the first set of measurements was made with the bark surface moistened, and the second set was made with the bark surface air-dried for a period of 30 minutes. These data represent continuous spectra of bark reflectance. Each sample was scanned three times, rotating the sample when possible. The reported values for each sample are an average over the three scans. The data are provided in tabular ASCII files. The data files are available on a CD-ROM (see document number 20010000884), or from the Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC).

Hall, Forrest G.↗
DOE OSTI2025

Learning and Controlling Silicon Dopant Transitions in Graphene Using Scanning Transmission Electron Microscopy

A machine learning approach is introduced to determine the transition dynamics of silicon atoms on a single layer of carbon atoms, when stimulated by the electron beam of a scanning transmission electron microscope (STEM). This method is data-centric, leveraging data collected on a STEM. The data samples are processed and filtered to produce symbolic representations, which is used to train a neural network to predict transition probabilities. These learned transition dynamics are then leveraged to guide a single silicon atom throughout the lattice to pre-determined target destinations. Empirical analyses are presented that demonstrate the efficacy and generality of the approach.

36 MATERIALS SCIENCE↗
NASA NTRS1998

Dynamic Models of Instruments Using Rotating Unbalanced Masses

The motion of telescopes, satellites, and other flight bodies have been controlled by various means in the past. For example, gimbal mounted devices can use electric motors to produce pointing and scanning motions. Reaction wheels, control moment gyros, and propellant-charged reaction jets are other technologies that have also been used. Each of these methods has its advantages, but all actuator systems used in a flight environment face the challenges of minimizing weight, reducing energy consumption, and maximizing reliability. Recently, Polites invented and patented the Rotating Unbalanced Mass (RUM) device as a means for generation scanning motion on flight experiments. RUM devices together with traditional servomechanisms have been successfully used to generate various scanning motions: linear, raster, and circular. The basic principle can be described: A RUM rotating at constant angular velocity exerts a cyclic centrifugal force on the instrument or main body, thus producing a periodic scanning motion. A system of RUM devices exerts no reaction forces on the main body, requires very little energy to rotate the RUMS, and is simple to construct. These are significant advantages over electric motors, reaction wheels, and control moment gyroscopes. Although the RUM device very easily produces scanning motion, an auxiliary control system has been required to maintain the proper orientation, or pointing of the main body. It has been suggested that RUM devices can be used to control pointing dynamics, as well as generate the desired periodic scanning motion. The idea is that the RUM velocity will not be kept constant, but will vary over the period of one RUM rotation. The thought is that the changing angular velocity produces a centrifugal force having time-varying magnitude and direction. The scope of this ongoing research project is to study the pointing control concept, and recommend a direction of study for advanced pointing control using only RUM devices. This report is subdivided into three sections. Three dynamic models and one proposed control principle are described first. Then, the results of model analyses and some experiments are discussed. Finally, suggestions for future work are presented.

Hung, John Y.↗
NASA NTRS1984

Effects of the motions of a platform-mounted payload on the nutational stability of a dual-spin spacecraft - A Galileo case study

In the presence of spacecraft nutation, tracking of an inertially fixed target by the Galileo scan platform requires the use of two control loops to move the scan platform and the stator in such a way as to compensate for spacecraft motion. The effect of these control loops on spacecraft nutational stability is examined using an eigenvalue analysis approach as well as several computer analysis packages. It was found that the actions of these control loops tend to drive nutation to the point of neutralizing, and even overpowering the damping actions of the spacecraft nutation damper, for pointing directions close to the spacecraft's poles. Stable and unstable zones are mapped out for two sets of spacecraft mass properties, and contributions of rotor asymmetry and stator flexibility are also discussed.

Man, G. K.↗
NASA NTRS1981

Visual scanning behavior and pilot workload

An experimental paradigm and a set of results which demonstrate a relationship between the level of performance on a skilled man-machine control task, the skill of the operator, the level of mental difficulty induced by an additional task imposed on the basic control task, and visual scanning performance. During a constant, simulated piloting task, visual scanning of instruments was found to vary as a function of the level of difficulty of a verbal mental loading task. The average dwell time of each fixation on the pilot's primary instrument increased as a function of the estimated skill level of the pilots, with novices being affected by the loading task much more than the experts. The results suggest that visual scanning of instruments in a controlled task may be an indicator of both workload and skill.

Harris, R. L., Sr.↗
NASA NTRS1992

Automated Weld Characterization Using the Thermoelectric Method

The effective assessment of the integrity of welds is a complicated NDE problem that continues to be a challenge. To be able to completely characterize a weld, detailed knowledge of its tensile strength, ductility, hardness, microstructure, macrostructure, and chemical composition is needed. NDE techniques which can provide information on any of these features are extremely important. In this paper, we examine a seldom used approach based on the thermoelectric (TE) effect for characterizing welds and their associated heat affected zone (HAZ). The thermoelectric method monitors the thermoelectric power which is sensitive to small changes in the kinetics of the conduction electrons near the Fermi surface that can be caused by changes in the local microstructure. The technique has been applied to metal sorting, quality testing, flaw detection, thickness gauging of layers, and microscopic structural analysis. To demonstrate the effectiveness of the technique for characterizing welds, a series of tungsten-inert-gas welded Inconel-718 samples were scanned with a computer controlled TE probe. The samples were then analyzed using a scanning electron microscope and Rockwell hardness tests to characterize the weld and the associated HAZ. We then correlated the results with the TE measurements to provide quantitative information on the size of the HAZ and the degree of hardness of the material in the weld region. This provides potentially valuable information on the strength and fatigue life of the weld. We begin the paper by providing a brief review of the TE technique and then highlight some of the factors that can effect the measurements. Next, we provide an overview of the experimental procedure and discuss the results. Finally, we summarize our findings and consider areas for future research.

Fulton, J. P.↗
NASA NTRS1975

A coherent light scanner for optical processing of large format transparencies

A laser scanner is discussed in which the scanning beam is random-access addressable and perpendicular to the image input plane and the irradiance of the scanned beam is controlled so that a constant average irradiance is maintained after passage through the image plane. The scanner's optical system and design are described, and its performance is evaluated. It is noted that with this scanner, data in the form of large-format transparencies can be processed without the expense, space, maintenance, and precautions attendant to the operation of a high-power laser with large-aperture collimating optics. It is shown that the scanned format as well as the diameter of the scanning beam may be increased by simple design modifications and that higher scan rates can be achieved at the expense of resolution by employing acousto-optic deflectors with different relay optics.

Callen, W. R.↗
NASA NTRS1982

Visual scanning behavior and pilot workload

This paper describes an experimental paradigm and a set of results which demonstrate a relationship between the level of performance on a skilled man-machine control task, the skill of the operator, the level of mental difficulty induced by an additional task imposed on the basic control task, and visual scanning performance. During a constant, simulated piloting task, visual scanning of instruments was found to vary with the difficulty of a verbal mental loading task. The average dwell time of each fixation on the pilot's primary instrument increased with the estimated skill level of the pilots, with novices being affected by the loading task much more than experts. The results suggest that visual scanning of instruments in a controlled task may be an indicator of both workload and skill.

Harris, R. L., Sr.↗
NASA NTRS1990

Rotating-unbalanced-mass Devices for Scanning Balloon-borne Experiments, Free-flying Spacecraft, and Space Shuttle/space Station Experiments

A new method is presented for scanning balloon-borne experiments, free-flying spacecraft, and gimballed experiments mounted to the space shuttle or the space station. It uses rotating-unbalanced-mass (RUM) devices for generating circular, line, or raster scan patterns and an auxiliary control system for target acquisition, keeping the scan centered on the target, and producing complementary motion for raster scanning. It is ideal for applications where the only possible way to accomplish the required scan is to physically scan the entire experiment or spacecraft as in x ray and gamma ray experiments. In such cases, this new method should have advantages over prior methods in terms of either power, weight, cost, performance, stability, or a combination of these.

Polites, Michael E.↗
NASA NTRS1991

New method for scanning spacecraft and balloon-borne/space-based experiments

A new method is presented for scanning balloon-borne experiments, free-flying spacecraft, and gimballed experiments mounted to the space shuttle or the space station. It uses rotating-unbalanced-mass (RUM) devices for generating circular, line, or raster scan patterns and an auxiliary control system for target acquisition, keeping the scan centered on the target, and producing complementary motion for raster scanning. It is ideal for applications where the only possible way to accomplish the required scan is to physically scan the entire experiment or spacecraft as in X-ray and gamma ray experiments. In such cases, this new method should have advantages over prior methods in terms of either power, weight, cost, performance, stability, or a combination of these.

Polites, Michael E.↗
NASA NTRS1982

Visual scanning behavior and mental workload in aircraft pilots

This paper describes an experimental paradigm and a set of preliminary results which demonstrate a relationship between the level of performance on a skilled man-machine control task, the skill of the operator, the level of mental difficulty induced by an additional task imposed on the basic control task, and visual scanning performance. During a constant, simulated piloting task, visual scanning of instruments was found to vary as a function of the level of difficulty of a verbal loading task. The average dwell time of each fixation on the pilot's primary instrument increased as a function of the loading. The scanning behavior was also a function of the estimated skill level of the pilots, with novices being affected by the loading task much more than experts. The results suggest that visual scanning of instruments in a controlled task may be an indicator of both workload and skill.

Tole, J. R.↗
DOE OSTI2022

High resolution atomic force microscopy with an active piezoelectric microcantilever

Active microcantilevers with on-chip sensing and actuation provide significant advantages in tapping mode Atomic Force Microscopy (AFM). Collocated transduction allows for effective manipulation of cantilever dynamics through feedback control, enabling higher scan rates. However, the adjacency of the sensing and actuation electrodes is known to result in a high level of feedthrough, leading to a low imaging resolution. Readout circuit noise further deteriorates the imaging precision. Here, we investigate the noise sources that affect AFM microcantilevers with collocated aluminum nitride (AlN) actuator–sensor pairs. We reported these cantilevers in earlier work and demonstrated that they display a very low level of feedthrough between the actuation and sensing electrodes. We present a high signal-to-noise ratio (SNR) sensing method that enables us to demonstrate high-resolution AFM on a calibration grating with nm-step silicon carbide (SiC) terraces. In conclusion, measuring the Lorentzian response of the cantilever’s Brownian motion with the on-chip active sensor at resonance enables us to calibrate the dynamic stiffness at the first fundamental resonance mode, without utilizing an optical sensor.

47 OTHER INSTRUMENTATION↗
NASA NTRS1972

Surface colour photometry of galaxies with Schmidt telescopes.

A method is described which owes its practicality to the capability of Schmidt telescopes to record a number of galaxy images on a single plate and to the existence of high speed computer controlled area-scanning precision microdensitometers such as the Photometric Data Systems model 1010. The method of analysis results in quantitative color-index information which is displayed in a manner that allows any user to effectively study the morphological properties of the distribution of color-index in galaxies.

Wray, J. D.↗
NASA NTRS1974

A balloon-borne cryogenically cooled filter radiometer

The development of a cryogenically cooled filter radiometer for use with high altitude balloons is discussed. The radiometer has features which include the options for remote operation of two filter wheels each containing six filters at helium temperature and a cryogenic rotary chopper which may be run at 200 cycles per second or positioned open or closed, and a remotely operable chopped blackbody calibration source. The radiometer contains a ten inch diameter liquid nitrogen cooled Cassegrain telescope with nine individually filtered field stops in the focal plane. The telescope is mounted on a two-axis servo operated gimbal which is used to make sky scans under the control of an onboard programmer.

Debell, A. G.↗
NASA NTRS1977

Calibration of Viking imaging system pointing, image extraction, and optical navigation measure

Pointing control and knowledge accuracy of Viking Orbiter science instruments is controlled by the scan platform. Calibration of the scan platform and the imaging system was accomplished through mathematical models. The calibration procedure and results obtained for the two Viking spacecraft are described. Included are both ground and in-flight scan platform calibrations, and the additional calibrations unique to optical navigation.

Breckenridge, W. G.↗