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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 523 records · Page 29
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

High-performance visible/UV CCD focal plane technology for spacebased applications

We describe recent technology developments aimed at large CCD imagers for space based applications in the visible and UV. Some of the principal areas of effort include work on reducing device degradation in the natural space-radiation environment, improvements in quantum efficiency in the visible and UV, and larger-device formats. One of the most serious hazards for space based CCD's operating at low signal levels is the displacement damage resulting from bombardment by energetic protons. Such damage degrades charge-transfer efficiency and increases dark current. We have achieved improved hardness to proton-induced displacement damage by selective ion implants into the CCD channel and by reduced temperature of operation. To attain high quantum efficiency across the visible and UV we have developed a technology for back-illuminated CCD's. With suitable antireflection (AR) coatings such devices have quantum efficiencies near 90 percent in the 500-700-nm band. In the UV band from 200 to 400 nm, where it is difficult to find coatings that are sufficiently transparent and can provide good matching to the high refractive index of silicon, we have been able to substantially increase the quantum efficiency using a thin film of HfO2 as an AR coating. These technology efforts were applied to a 420 x 420-pixel frame-transfer imager, and future work will be extended to a 1024 x 1024-pixel device now under development.

Burke, B. E.↗
NASA NTRS2012

Thermal Imaging with Novel Infrared Focal Plane Arrays and Quantitative Analysis of Thermal Imagery

We have developed a single long-wavelength infrared (LWIR) quantum well infrared photodetector (QWIP) camera for thermography. This camera has been used to measure the temperature profile of patients. A pixel coregistered simultaneously reading mid-wavelength infrared (MWIR)/LWIR dual-band QWIP camera was developed to improve the accuracy of temperature measurements especially with objects with unknown emissivity. Even the dualband measurement can provide inaccurate results due to the fact that emissivity is a function of wavelength. Thus we have been developing a four-band QWIP camera for accurate temperature measurement of remote object.

Thermography↗
DOE OSTI2020

Loop Antennas for Use On/Off Ground Planes

Many applications benefit from the ability of an RFID tag to operate both on and off a conducting ground plane. This paper presents an electrically small loop antenna at 433 MHz that passively maintains its free-space tune and match when located a certain distance away from a large conducting ground plane. The design achieves this using a single radiation mechanism (that of a loop) in both environments without the use of a ground plane or EBG/AMC structure. An equivalent circuit model is developed that explains the dual-environment behavior and shows that the geometry balances inductive and capacitive parasitics introduced by the ground plane such that the free-space loop reactance, and thus resonant frequency, does not change. A design equation for balancing the inductive and capacitive parasitic effects is derived. Finally, experimental data showing the design eliminates ground plane detuning in practice is presented. The design is suitable for active, “hard” RFID tag applications.

42 ENGINEERING↗
NASA NTRS2003

A miniature mass spectrometer for hydrazine detection

A Miniature Mass Spectrometer (MMS) with a focal plane (Mattauch-Herzog) geometry has been developed at the Jet Propulsion Laboratory. The MMS has the potential to meet the NASA requirements of 10 parts per billion sensitivity for Hydrazine detection, as well as the requirements for instant response, portability, and low maintenance.

MMS Miniature Mass Spectrometer hydrazine detectio↗
NASA NTRS1992

Analytic orbit plane targeting for orbit transfers about an oblate planet

This paper develops closed-form expressions which accurately model variations in orbital inclination and longitude of the ascending node due to the influence of the J2 oblateness perturbation. These analytic expressions are particularly useful in defining perturbed orbit transfer planes which naturally regress into the target intercept position for Lambert-type transfers and in compensating for differential nodal regression between two orbiting vehicles in rendezvous targeting problems. Results of example problems for each of these scenarios demonstrate that they accurately compensate for these oblateness effects.

Mchenry, R. L.↗
NASA NTRS1986

The development of optimal control laws for orbiting tethered platform systems

A mathematical model of the open and closed loop in-orbit plane dynamics of a space platform-tethered-subsatellite system is developed. The system consists of a rigid platform from which an (assumed massless) tether is deploying (retrieving) a subsatellite from an attachment point which is, in general, offset from the platform's mass center. A Lagrangian formulation yields equations describing platform pitch, subsatellite tether-line swing, and varying tether length motions. These equations are linearized about the nominal station keeping motion. Control can be provided by both modulation of the tether tension level and by a momentum type platform-mounted device; system controllability depends on the presence of both control inputs. Stability criteria are developed in terms of the control law gains, the platform inertia ratio, and tether offset parameter. Control law gains are obtained based on linear quadratic regulator techniques. Typical transient responses of both the state and required control effort are presented.

Bainum, P. M.↗
DOE OSTI2016

Nanoscale effects in the characterization of viscoelastic materials with atomic force microscopy: Coupling of a quasi-three-dimensional standard linear solid model with in-plane surface interactions

Significant progress has been accomplished in the development of experimental contact-mode and dynamic-mode atomic force microscopy (AFM) methods designed to measure surface material properties. However, current methods are based on one-dimensional (1D) descriptions of the tip-sample interaction forces, thus neglecting the intricacies involved in the material behavior of complex samples (such as soft viscoelastic materials) as well as the differences in material response between the surface and the bulk. In order to begin to address this gap, a computational study is presented where the sample is simulated using an enhanced version of a recently introduced model that treats the surface as a collection of standard-linear-solid viscoelastic elements. The enhanced model introduces in-plane surface elastic forces that can be approximately related to a two-dimensional (2D) Young's modulus. Relevant cases are discussed for single-and multifrequency intermittent-contact AFM imaging, with focus on the calculated surface indentation profiles and tip-sample interaction force curves, as well as their implications with regards to experimental interpretation. A variety of phenomena are examined in detail, which highlight the need for further development of more physically accurate sample models that are specifically designed for AFM simulation. As a result, a multifrequency AFM simulation tool based on the above sample model is provided as supporting information.

36 MATERIALS SCIENCE↗
NASA NTRSDate not supplied

Tendon-Actuated Lightweight In-Space MANipulator (TALISMAN) Hinge Joint Structural Performance

The Tendon Actuated Lightweight In-Space MANipulator (TALISMAN), invented and initially developed under the Space Technology Mission Directorate Human Robotics Systems program, is a tendon-actuated robot that established a new structural architecture for long-reach space manipulators. The TALISMAN is designed to have significant stiffness and strength in the plane of the tendons or cables, and operations are designed such that all primary loads are applied in that same plane. However, during normal operations it is possible for out-of-plane forces to be applied on the TALISMAN when secondary loads are imparted by a tool or action at the wrist. These secondary loading conditions will induce out-of-plane bending loads in the TALISMAN hinge joints. The TALISMAN hinge joints must be designed for these out-of-plane loads, to ensure no failure of the joint occurs during operations. A series hinge joint out-of-plane stiffness tests were conducted at five different joint angles; at three cable pre-loads from 25-lbf to 100-lbf; up to an equivalent out-of-plane tip load of 27.28-lbf at the end of a 51-in. long distal link. The objective of the tests was to provide an initial set of deflection, cable load, and strain data to inform accurate modeling of the hinge joint out-of-plane stiffness. The test objective was achieved by developing an FEM of the hinge joint able to predict tip displacement to within 10% of values measured in tests. The hinge joint FEM may now be implemented into a full-scale analysis model of the TALISMAN V2.0 to provide predictions of out-of-plane displacement under different load and joint angle conditions.

Matthew K Mahlin↗
NASA NTRS1998

Quantum Well Infrared Photodetector (QWIP) Focal Planes for Long Wave Imaging

In this paper, we discuss the development of very sensitive long wavelength infrared GaAs/AlxGa1-xAs quantum well infrared photodetectors (QWIPs) based on bound-to-quasibound intersubband transition, fabrication of light coupling schemes for efficient light coupling, and demonstration of several long wavelength infrared cameras based on QWIP focal plane arrays.

long wavelength infrared quantum well infrared pho↗
DOE OSTI2018

Development of Discharge in a Saline Solution at Near-Threshold Voltages

The development of a discharge in a point−plane gap filled with a saline solution with a salt content of 3% was studied experimentally. The duration of the voltage pulse applied to the gap was about 2 ms. Data are presented on the formation dynamics of gas microcavities at near-threshold voltages at which gas-discharge plasma appears in some microcavities. The cavities are conglomerates of microbubbles with a typical size of ≈100 μm. At the threshold voltage (≈750 V), the active electrode is covered with a gas layer and the gap voltage is in fact applied to this layer, which leads to the development of discharges in individual microbubbles. In this case, the discharge operates in the form of short current pulses. The number of microcavities filled with plasma increases as the voltage grows above the threshold value. At the plasma boundary, new microbubbles are formed, in which discharges are ignited. As a result, the plasma front propagates from the active electrode into the gap with a characteristic velocity of 10{sup 3} cm/s.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
NASA NTRS1994

An optical technique for examining aircraft shock wave structures in flight

The detailed properties of sonic booms have to be better understood before commercial, next generation, supersonic and hypersonic aircraft can be properly developed. Experimental tests and measurements are needed to help sort the physical details of the flows at realistic test conditions. Some of these tests can be made in wind tunnels, but the need for full flight conditions simulation, the problem of tunnel wall interference, and the short distance the shocks can be examined from the aircraft, limit the usefulness of wind tunnel tests. Previous measurement techniques for examining the flow field of aircraft in flight have included pressure measurements on the aircraft, ground based pressure measurements, and flow field measurements made with chase aircraft. Obtaining data with chase planes is a slow and difficult process, and is limited in how close it can be obtained to the test aircraft. A need clearly existed for a better technique to examine the shock structure from the plane to large distances from the plane. A new technique has been recently developed to obtain schlieren photographs of aircraft in flight (SAF). Preliminary results have been obtained, and the technique holds promise as a tool to study the shape and approximate strength of the shock wave structure around the test aircraft, and examine shock wave details all the way from the aircraft to near the ground. The current paper describes this approach, and gives some preliminary test results.

Weinstein, Leonard M.↗
DOE OSTI2018

Corresponding Orbitals Derived from Periodic Bloch States for Electron Transfer Calculations of Transition Metal Oxides

An approach for modeling electron transfer in solids and at surfaces of iron - (oxy- hydr)oxides and other redox active solids has been developed for electronic structure methods (i.e., plane-wave DFT) capable of performing ab initio molecular dynamics eciently with periodic cells and large system sizes while at the same time being accurate enough to be used in the estimation of the electron-transfer coupling matrix element, VAB, and the electron transfer transmission factor, el. This method is an extension of the valence bond theory ET method for molecules and clusters, imple- mented by Dupuis and co-workers and used extensively by Rosso and co-workers, in which scaled corresponding orbitals derived from the Bloch states are used to calculate the o-diagonal matrix elements HAB and SAB. A key development of the present work is the formulation of algorithms to improve of the accuracy of integration of the exact exchange integral in periodic boundary conditions. This method is demonstrated on model systems for electron small polaron transfer in iron-(oxyhydr)oxides, including bare Fe2+{Fe3+ ions, and in [Fe3+(OH2)2(OH)2)]n+ n chains representing the common edge-sharing Fe octahedral motif in these materials.

Bylaska, Eric J.↗
NASA NTRS1977

Developments in fracture mechanics test methods standardization; Proceedings of the Symposium, St. Louis, Mo., May 4, 1976

Experience in plane-strain fracture toughness testing per ASTM Method E 399 is considered along with fracture toughness testing using the C-shaped specimen, an analysis of radially cracked ring segments subject to forces and couples, compliance calibration of specimens used in the R-curve practice, heavy-section fracture toughness screening specimen, and sharply notched cylindrical tension specimens for screening plane-strain fracture toughness. Attention is also given to an investigation of some problems in developing standards for precracked Charpy specimen strength ratios, fracture testing with surface crack specimens, and the estimation of plane strain fracture toughness values from slow bend precracked Charpy specimen strength ratios.

Brown, W. F., Jr.↗
DOE OSTI2016

Scattering of radio frequency waves by cylindrical density filaments in tokamak plasmas

In tokamak fusion plasmas, coherent fluctuations in the form of blobs or filaments are routinely observed in the scrape-off layer. Radio frequency (RF) electromagnetic waves, excited by antenna structures placed near the wall of a tokamak, have to propagate through the scrape-off layer before reaching the core of the plasma. While the effect of fluctuations on the properties of RF waves has not been quantified experimentally, it is of interest to carry out a theoretical study to determine if fluctuations can affect the propagation characteristics of RF waves. Usually, the difference between the plasma density inside the filament and the background plasma density is sizable, the ratio of the density difference to the background density being of order one. Generally, this precludes the use of geometrical optics in determining the effect of fluctuations, since the relevant ratio has to be much less than one, typically, of the order of 10% or less. In this study, a full-wave, analytical model is developed for the scattering of a RF plane wave by a cylindrical plasma filament. It is assumed that the plasma inside and outside the filament is cold and uniform and that the major axis of the filament is aligned along the toroidal magnetic field. The ratio of the density inside the filament to the density of the background plasma is not restricted. The theoretical framework applies to the scattering of any cold plasma wave. In order to satisfy the boundary conditions at the interface between the filament and the background plasma, the electromagnetic fields inside and outside the filament need to have the same k ∥ , the wave vector parallel to the ambient magnetic field, as the incident plane wave. Consequently, in contrast to the scattering of a RF wave by a spherical blob [Ram et al., Phys. Plasmas 20, 056110-1–056110-10 (2013)], the scattering by a field-aligned filament does not broaden the k ∥ spectrum. However, the filament induces side-scattering leading to surface waves and can also couple some power to the cold plasma wave different from the incident wave. The changes induced by a filament in the propagation of electron cyclotron waves and lower hybrid waves are illustrated by numerical results displaying the properties of the Poynting vector. The Poynting flux in the wake of the filament, and directed towards the core of the plasma, develops a spatial structure due to diffraction and shadowing. Finally and thus, the fluctuations affect the uniformity of power flow into the plasma.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS2016

Band Engineering, Growth and Characteristics of Type-II InAs/GaSb Superlattice-Based Detectors

We report on band engineering, growth and device performance of infrared photodetectors based on type II InAs/Ga(In)Sb strain layer superlattices (SLs) using the complementary barrier infrared detector (CBIRD) design. The unipolar barriers on either side of the absorber in the CBIRD design in combination with the type-II InAs/GaSb superlattice material system are expected to outperform traditional III-V LWIR (Long-Wave InfraRed) imaging technologies and offer significant advantages over the conventional II-VI material based FPAs (Focal Plane Arrays). The innovative design of CBIRDS, barrier and band offset engineering , low defect density material growth, and robust fabrication processes have resulted in the development of high performance long wave infrared (LWIR) focal plane arrays at JPL (Jet Propulsion Laboratory).

Khoshakhlagh, A.↗