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At least 1,225 records · Page 68
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Stripline feed for a microstrip array of patch elements with teardrop shaped probes

A circularly polarized microstrip array antenna utilizing a honeycomb substrate made of dielectric material to support on one side the microstrip patch elements in an array, and on the other side a stripline circuit for feeding the patch elements in subarray groups of four with angular orientation and phase for producing circularly polarized radiation, preferably at a 0, 90, 180, and 270 degree relationship is described. The probe used for coupling each feed point in the stripline circuit to a microstrip patch element is teardrop shaped in order to introduce capacitance between the coupling probe and the metal sheet of the stripline circuit that serves as an antenna ground plane. The capacitance thus introduced tunes out inductance of the probe. The shape of the teardrop probe is not critical. The probe capacitance required is controlled by the maximum diameter for the teardrop shaped probe, which can be empirically determined for the operating frequency. An aluminum baffle around each subarray blocks out surface wave between subarrays.

Huang, John↗
NASA NTRS2004

Testing the Predictive Capability of the High-Fidelity Generalized Method of Cells Using an Efficient Reformulation

The High-Fidelity Generalized Method of Cells is a new micromechanics model for unidirectionally reinforced periodic multiphase materials that was developed to overcome the original model's shortcomings. The high-fidelity version predicts the local stress and strain fields with dramatically greater accuracy relative to the original model through the use of a better displacement field representation. Herein, we test the high-fidelity model's predictive capability in estimating the elastic moduli of periodic composites characterized by repeating unit cells obtained by rotation of an infinite square fiber array through an angle about the fiber axis. Such repeating unit cells may contain a few or many fibers, depending on the rotation angle. In order to analyze such multi-inclusion repeating unit cells efficiently, the high-fidelity micromechanics model's framework is reformulated using the local/global stiffness matrix approach. The excellent agreement with the corresponding results obtained from the standard transformation equations confirms the new model's predictive capability for periodic composites characterized by multi-inclusion repeating unit cells lacking planes of material symmetry. Comparison of the effective moduli and local stress fields with the corresponding results obtained from the original Generalized Method of Cells dramatically highlights the original model's shortcomings for certain classes of unidirectional composites.

Arnold, Steven M.↗
NASA NTRS2011

Multi-Segment Radius Measurement Using an Absolute Distance Meter Through a Null Assembly

This system was one of the test methods considered for measuring the radius of curvature of one or more of the 18 segmented mirrors that form the 6.5 m diameter primary mirror (PM) of the James Webb Space Telescope (JWST). The assembled telescope will be tested at cryogenic temperatures in a 17-m diameter by 27-m high vacuum chamber at the Johnson Space Center. This system uses a Leica Absolute Distance Meter (ADM), at a wavelength of 780 nm, combined with beam-steering and beam-shaping optics to make a differential distance measurement between a ring mirror on the reflective null assembly and individual PM segments. The ADM is located inside the same Pressure-Tight Enclosure (PTE) that houses the test interferometer. The PTE maintains the ADM and interferometer at ambient temperature and pressure so that they are not directly exposed to the telescope s harsh cryogenic and vacuum environment. This system takes advantage of the existing achromatic objective and reflective null assembly used by the test interferometer to direct four ADM beamlets to four PM segments through an optical path that is coincident with the interferometer beam. A mask, positioned on a linear slide, contains an array of 1.25 mm diameter circular subapertures that map to each of the 18 PM segments as well as six positions around the ring mirror. A down-collimated 4 mm ADM beam simultaneously covers 4 adjacent PM segment beamlets and one ring mirror beamlet. The radius, or spacing, of all 18 segments can be measured with the addition of two orthogonally-oriented scanning pentaprisms used to steer the ADM beam to any one of six different sub-aperture configurations at the plane of the ring mirror. The interferometer beam, at a wavelength of 687 nm, and the ADM beamlets, at a wavelength of 780 nm, pass through the objective and null so that the rays are normally incident on the parabolic PM surface. After reflecting off the PM, both the ADM and interferometer beams return to their respective instruments on nearly the same path. A fifth beamlet, acting as a differential reference, reflects off a ring mirror attached to the objective and null and returns to the ADM. The spacings between the ring mirror, objective, and null are known through manufacturing tolerances as well as through an in situ null wavefront alignment of the interferometer test beam with a reflective hologram located near the caustic of the null. Since total path length between the ring mirror and PM segments is highly deterministic, any ADM-measured departures from the predicted path length can be attributed to either spacing error or radius error in the PM. It is estimated that the path length measurement between the ring mirror and a PM segment is accurate to better than 100 m. The unique features of this invention include the differential distance measuring capability and its integration into an existing cryogenic and vacuum compatible interferometric optical test.

Merle, Cormic↗
NASA NTRS1986

Design and performance of 4 x 5120-element visible and 2 x 2560-element shortwave infrared multispectral focal planes

Two solid-state sensors for use in remote sensing instruments operating in the pushbroom mode are examined. The design and characteristics of the visible/near-infrared (VIS/NIR) device and the short-wavelength infrared (SWIR) device are described. The VIS/NIR is a CCD imager with four parallel sensor lines, each 1024 pixel long; the chip design and filter system of the VIS/NIR are studied. The performance of the VIS/NIR sensor with mask and its system performance are measured. The SWIR is a dual-band line imager consisting of palladium silicide Schottky-barrier detectors coupled to CCD multiplexers; the performance of the device is analyzed. The substrate materials and layout designs used to assemble the 4 x 5120-element VIS/NIR array and the 2 x 2560-element SWIR array are discussed, and the planarity of the butted arrays are verified using a profilometer. The optical and electrical characteristics, and the placement and butting accuracy of the arrays are evaluated. It is noted that the arrays met or exceed their expected performance.

Tower, J. R.↗
NASA NTRS1981

Cartographic potential of a spacecraft line-array camera system - Stereosat

A study of the Stereosat mission, which may acquire analog/digital stereo image data of cartographic quality with linear array camera systems, is presented, with attention given to the Stereosat system and the mission parameters, the utilization of the Stereosat studies in order to indicate the nature and scope of the problems associated with recording image data of high geometric fidelity from spacecraft equipped with line array sensors, and the assessing of the possibilities of meeting the completeness and accuracy requirements of cartographic products. A 713-km circular, sun-synchronous, near polar orbit, with an inclination of 98.24 deg and a repeat cycle of 48 days is designed to insure global coverage of the earth's land masses during the three-year lifetime of the mission. Three cameras (fore, vertical, and aft looking), mounted so as to record stereotriplets for a 61.4 km wide swath at a nominal focal plane scale of 1:1,000,000, are considered. The IFOV of 15 m should be adequate for producing thematic and image maps at scales of 1:50,000 to 1:250,000. The value of the coverage to cartographers will be dictated by the accuracy of the digital image data, which is largely a function of satellite control.

Welch, R.↗
NASA NTRS1987

A digital video model deformation system

The use of solid-state array cameras and a PC-controlled image acquisition system to measure model deformation in a wind tunnel is discussed. This digital system improves an earlier video model deformation system that used high-resolution tube cameras and required the manual measurement of targets on video hardcopy images. The new system eliminates both the vibration-induced distortion associated with tube cameras and the manual readup of video images necessary in the earlier version. Camera calibration and data reduction procedures necessary to convert pixel image plane data from two cameras into wing deflections are presented. Laboratory tests to establish the uncertainty of the system with the geometry to be used are described.

Burner, A. W.↗
NASA NTRS1989

An experimental study of forced streamwise vortical structures in a plane mixing layer

Streamwise structures have been shown to ride among the primary spanwise vortices in past flow visualization investigations of plane mixing layers. More recently, quantitative measurements were obtained which showed the origin and evolution of streamwise vortices within a mixing layer. In the present study, the effects of perturbing the mixing layer using two different mechanisms are investigated. A serration on the splitter plate trailing edge was found to have a relatively small effect, confined to the near-field development of the streamwise structures. The installation of cylindrical pegs in the high-speed side boundary layer, however, not only generated a regular array of vortex pairs, but also affected the mean development of the mixing layer far downstream. In both cases, the mean streamwise vorticity was found to decay rapidly with increasing downstream distance.

Mehta, Rabindra D.↗
NASA NTRS2004

Swift/BAT Calibration and Spectral Response

The Burst Alert Telescope (BAT) aboard NASA#s Swift Gamma-Ray Burst Explorer is a large coded aperture gamma-ray telescope consisting of a 2.4 m (8#) x 1.2 m (4#) coded aperture mask supported 1 meter above a 5200 square cm area detector plane containing 32,768 individual 4 mm x 4 mm x 2 mm CZT detectors. The BAT is now completely assembled and integrated with the Swift spacecraft in anticipation of an October 2004 launch. Extensive ground calibration measurements using a variety of radioactive sources have resulted in a moderately high fidelity model for the BAT spectral and photometric response. This paper describes these ground calibration measurements as well as related computer simulations used to study the efficiency and individual detector properties of the BAT detector array. The creation of a single spectral response model representative of the fully integrated BAT posed an interesting challenge and is at the heart of the public analysis tool #batdrmgen# which computes a response matrix for any given sky position within the BAT FOV. This paper will describe the batdrmgen response generator tool and conclude with a description of the on-orbit calibration plans as well as plans for the future improvements needed to produce the more detailed spectral response model that is required for the construction of an all-sky hard x-ray survey.

Parsons, A.↗
NASA NTRS1993

Low impedance printed circuit radiating element

A printed circuit radiating element comprises a geometrically symmetric planar area of a conducting material separated from a ground plane by a dielectric medium. The driving point of the radiating element is at the base of a notch in one side thereof so that the driving impedance is reduced from that obtained when the element is driven at its edge. Symmetrically disposed on opposite sides of an axis of symmetry of the element along which the driving point lies are two notches which restore the electrical symmetry of the radiating element thereby to suppress higher order modes. The suppression of these higher order modes results in a radiation pattern with minimal cross-polarized energy in the principal planes and high port-to-port isolation which could not be achieved with an asymmetrical element. Two driving points may be employed with the radiating element to produce a dual linearly polarized antenna and a reactive combiner or hybrid may be employed to obtain circularly-polarized radiations. The shape of the radiating element may be square, rectangular or circular, for example, in accordance with the desired characteristics. A plurality of radiating elements may be interconnected via appropriate transmission paths to form an antenna array.

Rahm, James K.↗
NASA NTRS1986

Intensified-CCD focal plane detector for space applications A second generation

An intensified-CCD detector system developed for space applications from commercially available components is described. This detector uses components which are readily available and are mechanically, thermally, and optically coupled to produce the final compact system. The CCD is cooled using a Peltier-effect thermoelectric cooler to reduce thermal noise. The image is formed on the photocathode of a proximity-focused image intensifier and is transferred fiber-optically from the intensifier to the CDD. Various photocathode and window materials are used to optimize the system for use within the wavelength range extending from the far UV to the near IR. The basic design, including the image intensifier, intensifier-CCD interface, CCD array, cooling, electronics, and mounting, and the detector performance are described in detail.

Torr, M. R.↗
NASA NTRS2006

Polarimeter Arrays for Cosmic Microwave Background Measurements

We discuss general system architectures and specific work towards precision measurements of Cosmic Microwave Background (CMB) polarization. The CMB and its polarization carry fundamental information on the origin, structure, and evolution of the universe. Detecting the imprint of primordial gravitational radiation on the faint polarization of the CMB will be difficult. The two primary challenges will be achieving both the required sensitivity and precise control over systematic errors. At anisotropy levels possibly as small as a few nanokelvin, the gravity-wave signal is faint compared to the fundamental sensitivity limit imposed by photon arrival statistics, and one must make simultaneous measurements with large numbers, hundreds to thousands, of independent background-limited direct detectors. Highly integrated focal plane architectures, and multiplexing of detector outputs, will be essential. Because the detectors, optics, and even the CMB itself are brighter than the faint gravity-wave signal by six to nine orders of magnitude, even a tiny leakage of polarized light reflected or diffracted from warm objects could overwhelm the primordial signal. Advanced methods of modulating only the polarized component of the incident radiation will play an essential role in measurements of CMB polarization. One promising general polarimeter concept that is under investigation by a number of institutions is to first use planar antennas to separate millimeter-wave radiation collected by a lens or horn into two polarization channels. Then the signals can be fed to a pair of direct detectors through a planar circuit consisting of superconducting niobium microstrip transmission lines, hybrid couplers, band-pass filters, and phase modulators to measure the Stokes parameters of the incoming radiation.

Stevenson, Thomas↗
NASA NTRS2012

NASA Tech Briefs, April 2012

Topics include: Computational Ghost Imaging for Remote Sensing; Digital Architecture for a Trace Gas Sensor Platform; Dispersed Fringe Sensing Analysis - DFSA; Indium Tin Oxide Resistor-Based Nitric Oxide Microsensors; Gas Composition Sensing Using Carbon Nanotube Arrays; Sensor for Boundary Shear Stress in Fluid Flow; Model-Based Method for Sensor Validation; Qualification of Engineering Camera for Long-Duration Deep Space Missions; Remotely Powered Reconfigurable Receiver for Extreme Environment Sensing Platforms; Bump Bonding Using Metal-Coated Carbon Nanotubes; In Situ Mosaic Brightness Correction; Simplex GPS and InSAR Inversion Software; Virtual Machine Language 2.1; Multi-Scale Three-Dimensional Variational Data Assimilation System for Coastal Ocean Prediction; Pandora Operation and Analysis Software; Fabrication of a Cryogenic Bias Filter for Ultrasensitive Focal Plane; Processing of Nanosensors Using a Sacrificial Template Approach; High-Temperature Shape Memory Polymers; Modular Flooring System; Non-Toxic, Low-Freezing, Drop-In Replacement Heat Transfer Fluids; Materials That Enhance Efficiency and Radiation Resistance of Solar Cells; Low-Cost, Rugged High-Vacuum System; Static Gas-Charging Plug; Floating Oil-Spill Containment Device; Stemless Ball Valve; Improving Balance Function Using Low Levels of Electrical Stimulation of the Balance Organs; Oxygen-Methane Thruster; Lunar Navigation Determination System - LaNDS; Launch Method for Kites in Low-Wind or No-Wind Conditions; Supercritical CO2 Cleaning System for Planetary Protection and Contamination Control Applications; Design and Performance of a Wideband Radio Telescope; Finite Element Models for Electron Beam Freeform Fabrication Process Autonomous Information Unit for Fine-Grain Data Access Control and Information Protection in a Net-Centric System; Vehicle Detection for RCTA/ANS (Autonomous Navigation System); Image Mapping and Visual Attention on the Sensory Ego-Sphere; HyDE Framework for Stochastic and Hybrid Model-Based Diagnosis; and IMAGESEER - IMAGEs for Education and Research.

Source record↗
NASA NTRS1987

Measured noise of a scale model high speed propeller at simulated takeoff/approach conditions

A model high-speed advanced propeller, SR-7A, was tested in the NASA Lewis 9x15 foot anechoic wind tunnel at simulated takeoff/approach conditions of 0.2 Mach number. These tests were in support of the full-scale Propfan Text Assessment (PTA) flight program. Acoustic measurements were taken with fixed microphone arrays and with an axially translating microphone probe. Limited aerodynamic measurements were also taken to establish the propeller operating conditions. Tests were conducted with the propeller alone and with three down-stream wing configurations. The propeller was run over a range of blade setting angles from 32.0 deg. to 43.6 deg., tip speeds from 183 to 290 m/sec (600 to 950 ft/sec), and angles of attack from -10 deg. to +15 deg. The propeller alone BPF tone noise was found to increase 10 dB in the flyover plane at 15 deg. propeller axis angle of attack. The installation of the straight wing at minimum spacing of 0.54 wing chord increased the tone noise 5 dB under the wing of 10 deg. propeller axis angle of attack, while a similarly spaced inboard upswept wing only increased the tone noise 2 dB.

Woodward, Richard P.↗
NASA NTRS1987

Measured noise of a scale model high speed propeller at simulated takeoff/approach conditions

A model high-speed advanced propeller, SR-7A, was tested in the NASA Lewis 9 x 15 foot anechoic wind tunnel at simulated takeoff/approach conditions of 0.2 Mach number. These tests were in support of the full-scale Propfan Text Assessment (PTA) flight program. Acoustic measurements were taken with fixed microphone arrays and with an axially translating microphone probe. Limited aerodynamic measurements were also taken to establish the propeller operating conditions. Tests were conducted with the propeller alone and with three down-stream wing configurations. The propeller was run over a range of blade setting angles from 32.0 deg. to 43.6 deg., tip speeds from 183 to 290 m/sec (600 to 950 ft/sec), and angles of attack from -10 deg. to +15 deg. The propeller alone BPF tone noise was found to increase 10 dB in the flyover plane at 15 deg. propeller axis angle of attack. The installation of the straight wing at minimum spacing of 0.54 wing chord increased the tone noise 5 dB under the wing of 10 deg. propeller axis angle of attack, while a similarly spaced inboard upswept wing only increased the tone noise 2 dB.

Woodward, Richard P.↗
NASA NTRS1982

Extended range X-ray telescope: X-ray microscope design

A glancing incidence X-ray microscope using a confocal hyperboloid ellipsoid mirror was designed to couple optically a Wolter 1 telescope to a CCD focal plane detector. Both the RMS spot size and the point spread function calculations were used to evaluate the resolution, defocusing, and vignetting effects of the system for microscope focal lengths of 1, 1.5, and 2 meters and for magnifications varying from 2 to 10x. For the specific application with the S-056 telescope, a 2 meter, 8x microscope with a fabrication ratio of the microscope mirror length to the inner diameter at hyperboloid ellipsoid intersection of 2.5 was designed to be used with a thinned, back illuminated CCD detector array with 320 by 512, 30 micron pixels.

Shealy, D. L.↗
NASA NTRSDate not supplied

u-Spec Spectrometers for the EXCLAIM Instrument

The EXperiment for Cryogenic Large-aperture Intensity Mapping (EXCLAIM) is a cryogenic balloon-borne instrument that will map carbon monoxide and singly-ionized carbon emission lines across redshifts from 0to 3.5, using an intensity mapping approach. EXCLAIM will broaden our understanding of these elemental and molecular gases, and the role they play in star formation processes across cosmic time scales. The focal plane of EXCLAIM’s cryogenic telescope features sixμ-Spec spectrometers.μ-Spec is a compact, integrated grating-analog spectrometer, which uses meandered superconducting niobium microstrip transmission lines on a single-crystal silicon dielectric to synthesize the grating. It features superconducting aluminum microwave kinetic inductance detectors (MKIDs), also in a microstrip architecture. The spectrometers for EXCLAIM couple to the telescope optics via a hybrid planar antenna coupled to a silicon lenslet. The spectrometers operate from420−540 GHz with a resolving power R=λ/∆λ= 512, and employ an array of 355 MKIDs on each spectrometer. The spectrometer design targets a noise equivalent power (NEP) of 2×10−18W/√Hz (defined at the input to the main lobe of the spectrometer lenslet beam, within a 9◦half width), enabled by the cryogenic telescope environment, the sensitive MKID detectors, and the low dielectric loss of single-crystal silicon. We report on these spectrometers under development for EXCLAIM, providing an overview of the spectrometer and component designs, the spectrometer fabrication process, fabrication developments since previous prototype demonstrations, and the current status of their development for the EXCLAIM mission.

EXCLAIM Instrument↗
NASA NTRS1993

Specular scattering on a terrestrial playa and implications for planetary surface studies

Multiangle Advanced Solid State Array Spectroradiometer (ASAS) and Portable Apparatus for Rapid Acquisition of Bidirectional Observations of Land and Atmosphere (PARABOLA) visible and near infrared reflectance data covering the Lunar Lake playa, Nevada, were modeled using specular and volume scattering theory. The volume component used to model the data was based on the Hapke (1986) model and the specular scattering component was based on Fresnel reflection from surface facets with a distribution of tilts. Specular scattering was needed to explain the several-fold increase in reflectance observed at high phase angles in the solar principal plane. Results imply single scattering albedos of approximately 0.93 to 0.95, a real index of refraction value of approximately 1.52 (at a wavelength of 0.66 micron), a small imaginary index of refraction and an exponential facet tilt probability function for the playa. Electron micrographs showed th playa surface to consist of ensembles of smooth, micrometer-scale ellipsoidal particles on gently undulating topography at the millimeter to centimeter scale. The exponential probability function is consistent with this observation. Mars and the icy satellites are discussed as possible places to look for a significant specular scattering component.

Shepard, Michael K.↗
NASA NTRS1986

A Digital Video Model Deformation System

The use of slid-state array cameras and a PC controlled image acquisition system to measure model deformation in a wind tunnel is discussed. This digital system is an improvement to an earlier video model deformation system used at the National Transonic Facility (NTF) which employed high-resolution tube cameras and required the manual measurement of targets on video hardcopy images. The new system eliminates both the vibration-induced distortion associated with tube cameras and the manual readup of video images necessary in the earlier version. Camera calibration and data reduction procedures necessary to convert pixel image plane data from two cameras into wing deflections are presented. Laboratory tests to establish the uncertainty of the new system with the geometry to be used at the NTF are described.

Burner, A. W.↗