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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 NTRS2006

Electro-Optical Imaging Fourier-Transform Spectrometer

An electro-optical (E-O) imaging Fourier-transform spectrometer (IFTS), now under development, is a prototype of improved imaging spectrometers to be used for hyperspectral imaging, especially in the infrared spectral region. Unlike both imaging and non-imaging traditional Fourier-transform spectrometers, the E-O IFTS does not contain any moving parts. Elimination of the moving parts and the associated actuator mechanisms and supporting structures would increase reliability while enabling reductions in size and mass, relative to traditional Fourier-transform spectrometers that offer equivalent capabilities. Elimination of moving parts would also eliminate the vibrations caused by the motions of those parts. Figure 1 schematically depicts a traditional Fourier-transform spectrometer, wherein a critical time delay is varied by translating one the mirrors of a Michelson interferometer. The time-dependent optical output is a periodic representation of the input spectrum. Data characterizing the input spectrum are generated through fast-Fourier-transform (FFT) post-processing of the output in conjunction with the varying time delay.

Chao, Tien-Hsin↗
NASA NTRS1982

Integrated optics in an electrically scanned imaging Fourier transform spectrometer

An efficient, lightweight and stable, Fourier transform spectrometer was developed. The mechanical slide mechanism needed to create a path difference was eliminated by the use of retro-reflecting mirrors in a monolithic interferometer assembly in which the mirrors are not at 90 degrees to the propagation vector of the radiation, but rather at a small angle. The resulting plane wave fronts create a double-sided inteferogram of the source irradiance distribution which is detected by a charge-coupled device image sensor array. The position of each CCD pixel in the array is an indication of the path difference between the two retro-reflecting mirrors in the monolithic optical structure. The Fourier transform of the signals generated by the image sensor provide the spectral irradiance distribution of the source. For imaging, the interferometer assembly scans the source of irradiation by moving the entire instrument, such as would occur if it was fixedly mounted to a moving platform, i.e., a spacecraft. During scanning, the entrace slot to the monolithic optical structure sends different pixels to corresponding interferograms detected by adjacent columns of pixels of the image sensor.

Breckinridge, James B.↗
NASA NTRS1994

Investigations into mirror fabrication metrology analysis

This final report describes the work performed under this delivery order from June 1993 through August 1994. The scope of work included three distinct tasks in support of the AXAF-I program. The objective of the first task was to perform investigations of the grinding and polishing characteristics of the zerodur material by fabricating several samples. The second task was to continue the development of the integrated optical performance modeling software for AXAF-I. The purpose of third and final task was to develop and update the database of AXAF technical documents for an easy and rapid access. The MSFC optical and metrology shops were relocated from the B-wing of Building 4487 to Room BC 144 of Building 4466 in the beginning of this contract. This included dismantling, packing, and moving the equipment from its old location, and then reassembling it at the new location. A total of 65 zerodur samples, measuring 1 inch x 2 inches x 6 inches were ground and polished to a surface figure of lambda/10 p-v, and a surface finish of 5A rms were fabricated for coating tests. A number of special purpose tools and metal mirrors were also fabricated to support various AXAF-I development activities. In the metrology area, the ZYGO Mark 4 interferometer was relocated and also upgraded with a faster and more powerful processor. Surface metrology work was also performed on the coating samples and other optics using ZYGO interferometer and WYKO profilometer. A number of new features have been added to the GRAZTRACE program to enhance its analysis and modeling capabilities. A number of new commands have been added to the command mode GRAZTRACE program to provide a better control to the user on the program execution and data manipulation. Some commands and parameter entries have been reorganized for a uniform format. The command mode version of the convolution program CONVOLVE has been developed. An on-line help system and a user's manual have also been developed for the benefit of the users. The database of AXAF technical documents continues to progress. The titles, company name, date, and location of over 390 documents have been entered in this database. This database provides both a data search and retrieval function, and a data adding function. These functions allow a user to quickly search the data files for documents or add new information. A detailed user's guide has also been prepared. This user guide includes a document classification guide, a list of abbreviations, and a list of acronyms, which have been used in compiling this database of AXAF-I technical documents.

Dimmock, John O.↗
NASA NTRS2010

X-Ray Optics for the 2020's

X-ray optics is an essential and enabling technology for x-ray astronomy. This slide presentation presents the authors views on the requirements for x-ray optics as progress is made toward building IXO and preparing for the 2020's. The presentation reviews the status of several technologies that are being developed and outlines the steps that we as a community needs to take to move toward x-ray optics meeting the five key requirements: (1) high angular resolution, (2) large effective area, (3) low mass, (4) fast production, and (5) low cost. There is discussion of segmentation vs full shell, size of the mirror segment, mirror segment frabrication, post-slumping figure improvement, and characterization of coating quality.

Zhang, Will↗
NASA NTRSDate not supplied

Spectral Measurement Errors due to CCD Serial Pixel-to-Pixel Readout Interference in the Ocean Color Instrument of the NASA PACE Mission

The Ocean Color Instrument on NASA’s PACE mission is a hyperspectral imager with a spatial resolution of 1km x 1km and spectral resolution of 5nm in 2.5nm steps over 320-890nm. The detection system is based on two Charge-Coupled Devices (CCDs) operating in Time Delay Integration (TDI) mode to achieve high signal-to-noise ratio. The front-end optical imager is a rotating mirror-based system that images the ground-scene onto a slit with a field of view of 16km x 1km. The slit-image is re-imaged and wavelength dispersed on the CCDs. As the ground-scene moves through the slit, it moves along the CCD columns as charge is moved along with it. The accumulated charge at the end of each column is collected in a serial pixel. Each of the 16 CCD outputs read out 32 columns of the same ground scene spaced 0.625nm apart. The 32-pixel serial register is swiftly read out before the next TDI cycle. The telescope is spinning at 5.77Hz to achieve the required spatial resolution. This results in a serial pixel readout speed of 8.5MHz. Each serial read-cycle goes through a reset and video period that are each sampled to create a low-noise correlated double sample value. This only allows 59ns for the reset and video to be asserted and settled before sampling. Due to the short time period, the response of the CCD exhibits serial pixel-to-pixel readout interference as the reset and video signals do not have time to fully settle before sampling. Each serial pixel value therefore has a dependence on the value of the preceding pixel value. This leads to a spectral measurement error of up to 0.3%. We explain the operation of the detection system, the behavior of the interference and the resulting wavelength error with results from ground testing and on-orbit characterization.

Ulrik B Gliese↗
NASA NTRS1990

Numerical solution of the time-dependent kinetic equation for electrons in magnetized plasma

A numerical solution is developed for the time-dependent kinetic equation describing the evolution of arbitrary distributions of electrons injected into a magnetized plasma. Included in the equation are pitch-angle scattering and energy loss because of Coulomb collisions and magnetic mirroring. The numerical code can be easily modified to include other scattering or radiation terms. The numerical results are shown to agree well with known analytic solutions for various simplified configurations such as homogeneous injection in a homogeneous plasma, electron beams moving with small pitch angle with respect to the magnetic field, and injection into a magnetic trap.

Hamilton, Russell J.↗
NASA NTRS2005

Fabrication of Spherical Reflectors in Outer Space

A process is proposed for fabrication of lightweight spherical reflectors in outer space for telescopes, radio antennas, and light collectors that would be operated there. The process would obviate the relatively massive substrates and frames needed to support such reflectors in normal Earth gravitation. According to the proposal, fabrication of a reflector would begin with blowing of a bubble to the specified reflector radius. Taking advantage of the outer-space vacuum as a suitable environment for evaporative deposition of metal, a metal-evaporation source would be turned on and moved around the bubble to deposit a reflective metal film over the specified reflector area to a thickness of several microns. Then the source would be moved and aimed to deposit more metal around the edge of the reflector area, increasing the thickness there to approximately equal to 100 micron to form a frame. Then the bubble would be deflated and peeled off the metal, leaving a thin-film spherical mirror having an integral frame. The mirror would then be mounted for use. The feasibility of this technology has been proved by fabricating a prototype at JPL. As shown in the figure, a 2-in. (.5-cm) diameter hemispherical prototype reflector was made from a polymer bubble coated with silver, forming a very smooth surface.

Wang, Yu↗
NASA NTRS2004

Algorithm Determines Wind Speed and Direction from Venturi-Sensor Data

An algorithm computes the velocity of wind from the readings of an instrument like the one described in another Tech Brief. To recapitulate: The sensor has no moving parts and is a compact, rugged means of measuring wind vectors having magnitudes of as much as 300 mph (134 m/s). The sensor includes a Venturi gap bounded by a curved upper and a curved lower surface that are axisymmetric with respect to a vertical axis and mirror-symmetric with respect to a horizontal midplane. One of the curved surfaces is instrumented with multiple ports for measuring dynamic pressures. The sensor also incorporates auxiliary sensors for measuring temperature, relative humidity, and static atmospheric pressure. The design and operation of the sensor are based on the concepts of (1) using Bernoulli's equation (which expresses the relationship among variations of speed, density, and pressure along a streamline) to calculate the speed of the wind from differences among the pressure readings at the various ports; and (2) calculating the direction of the wind from the angular positions of ports selected according to comparisons among their pressure readings. The present algorithm performs these calculations.

Zysko, Jan A.↗
NASA NTRS1974

Single reflector interference spectrometer and drive system therefor

In a Fourier interference spectrometer of the doublepass retroreflector type, a single mirror is employed in the path of both split beams of an incoming ray to cause them to double back through separate retroreflectors. Changes in optical path length are achieved by linear displacement of both retroreflectors using a motor driven lead screw on one for large, low frequency changes, a moving-coil actuator on the other for smaller, mid-frequency changes and a piezoelectric actuator on one of these two for small, high frequency changes.

Schindler, R. A.↗
NASA NTRS2003

Three-Dimensional Venturi Sensor for Measuring Extreme Winds

A three-dimensional (3D) Venturi sensor is being developed as a compact, rugged means of measuring wind vectors having magnitudes of as much as 300 mph (134 m/s). This sensor also incorporates auxiliary sensors for measuring temperature from -40 to +120 F (-40 to +49 C), relative humidity from 0 to 100 percent, and atmospheric pressure from 846 to 1,084 millibar (85 to 108 kPa). Conventional cup-and-vane anemometers are highly susceptible to damage by both high wind forces and debris, due to their moving parts and large profiles. In addition, they exhibit slow recovery times contributing to an inaccurately high average-speed reading. Ultrasonic and hot-wire anemometers overcome some of the disadvantages of the cup and-vane anemometers, but they have other disadvantageous features, including limited dynamic range and susceptibility to errors caused by external acoustic noise and rain. In contrast, the novel 3D Venturi sensor is less vulnerable to wind damage because of its smaller profile and ruggedness. Since the sensor has no moving parts, it provides increased reliability and lower maintenance costs. It has faster response and recovery times to changing wind conditions than traditional systems. In addition, it offers wide dynamic range and is expected to be relatively insensitive to rain and acoustic energy. The Venturi effect in this sensor is achieved by the mirrored double-inflection curve, which is then rotated 360 to create the desired detection surfaces. The curve is optimized to provide a good balance of pressure difference between sensor ports and overall maximum fluid velocity while in the shape. Four posts are used to separate the two shapes, and their size and location were chosen to minimize effects on the pressure measurements. The 3D Venturi sensor has smart software algorithms to map the wind pressure exerted on the surfaces of the design. Using Bernoulli's equation, the speed of the wind is calculated from the differences among the pressure readings at the various ports. The direction of the wind is calculated from the spatial distribution and magnitude of the pressure readings. All of the pressure port sizes and locations have been optimized to minimize measurement errors and to reside in areas demonstrating a stable pressure reading proportional to the velocity range.

Zysko, Jan A.↗
NASA NTRS1982

Plasma pitch angle distributions near the substorm injection front

ATS-6 spacecraft hot plasma instrument data obtained during January, 1980 is presented, which provides electron and ion pitch distributions in the vicinity of an earthward-propagating, substorm-associated abrupt plasma change near synchronous orbit. Evidence is found of symmetric atmospheric source cones for few 100-eV electrons after front passage, supporting both (1) concept of atmospheric electron degradation of the hot, high-altitude plasma, and (2) the proposal that the injection front is a moving, precipitation-flow boundary between the hot plasma and the cooler plasma that has become spectrally degraded via interaction with the atmosphere. The enhanced hot plasma electron intensities appearing in association with front passage exhibit a modest, field-aligned anisotropy with minima at pitch angles characteristic of symmetric loss cones, consistent with mirror compression of the electrons on inward-collapsing field lines.

Moore, T. E.↗
NASA NTRS1986

Automatic Guidance for Remote Manipulator

Position sensor and mirror guides manipulator toward object. Grasping becomes automatic when sensor begins to receive signal from reflector on object to be manipulated. Light-emitting diodes on manipulator produce light signals for reflector, which is composite of plane and corner reflectors. Proposed scheme especially useful when manipulator arm tends to flex or when object is moving. Sensor and microprocessor designed to compensate for manipulatorarm oscillation.

Johnston, A. R.↗
NASA NTRS1996

Homochirality as the signature of life: the SETH Cigar

A characteristic hallmark of life is its homochirality: all biomolecules are usually of one hand, e.g. on Earth life uses only L-amino acids for protein synthesis and not their D mirror images. It is therefore suggested that a search for extra-terrestrial life can be approached as a Search for Extra-Terrestrial Homochirality (SETH). A novel miniaturized space polarimeter, called the SETH Cigar, is described which could he used to detect optical rotation as the homochiral signature of life on other planets. Moving parts are avoided by replacing the normal rotating polarizer by multiple fixed polarizers at different angles as in the eye of the bee. It is believed that homochirality will be found in the subsurface layers on Mars as a relic of extinct life.

NASA Center ARC↗
NASA NTRS1989

Deferred electronic heterodyne moire deflectometry: A method for transient density fields measurement

Effects of spherical aberrations of the mirror used in the moire system on the angular resolution of the system are investigated. It is shown that the spherical aberrations may reduce significantly the performance of the conventional moire deflectometer. However, due to the heterodyne procedure, this is not the case with the heterodyne moire system. A moire system with a constant speed moving grating is demonstrated. It is shown that the system readout is linear and the system does not need calibration. In addition, the repeatability of the measurements is improved in this system as compared to the sinusoidally moving grating setup. The problem of the photographic plates alignment is solved by using a mechanical system in which the plate is held firmly throughout the experiment and accurately replaced after removing for photographic processing. The effect of a circular detector's aperture size on readout was tested. It is shown that the spatial phase variations, observed when scanning along a straight moire fringe, may considerably be reduced. At present we may say that both the on-line and the deferred heterodyne moire techniques may reliably be used. The errors of phase readings are 1 deg and 5 deg for the on-line and deferred methods. The total error due to subtraction of two readings at each position is, therefore, 1.4 deg and 7 deg, respectively. Further research for improving the deferred system is suggested.

Stricker, Josef↗
NASA NTRS1993

Effect of jet engine exhaust on SOFIA straylight performance

The Stratospheric Observatory For Infrared Astronomy (SOFIA) is being designed at NASA's Ames Research Center as a replacement for the Kuiper Airborne Observatory (KAO). A 2.5-m Nasmyth telescope will be mounted in a Boeing 747 SP and flown at 41,000 ft, above most of the H2O in the earth's atmosphere. In the original SOFIA design, the telescope is located in front of the wings, as it is in the KAO. An alternative design with the telescope placed behind the wings is being studied as part of an effort to reduce cost and weight. In this location, the emission from the engines and the hot H2O molecules in the exhaust become significant straylight sources. The engines and exhaust radiate into the telescope cavity, and illuminate the primary and tertiary mirrors at low telescope elevation angles. The APART/PADE program was used to analyze the straylight at the SOFIA focal plane as a function of wavelength and telescope elevation angle. The emission from the engines and exhaust gas is compared to that from the earth and the telescope itself. Based on the results of this analysis, the SOFIA telescope has been moved behind the wings.

St. Clair Dinger, Ann↗
NASA NTRS1995

Wide scanning spherical antenna

A novel method for calculating the surface shapes for subreflectors in a suboptic assembly of a tri-reflector spherical antenna system is introduced, modeled from a generalization of Galindo-Israel's method of solving partial differential equations to correct for spherical aberration and provide uniform feed to aperture mapping. In a first embodiment, the suboptic assembly moves as a single unit to achieve scan while the main reflector remains stationary. A feed horn is tilted during scan to maintain the illuminated area on the main spherical reflector fixed throughout the scan thereby eliminating the need to oversize the main spherical reflector. In an alternate embodiment, both the main spherical reflector and the suboptic assembly are fixed. A flat mirror is used to create a virtual image of the suboptic assembly. Scan is achieved by rotating the mirror about the spherical center of the main reflector. The feed horn is tilted during scan to maintain the illuminated area on the main spherical reflector fixed throughout the scan.

Shen, Bing↗
NASA NTRS2013

Practical UAV Optical Sensor Bench with Minimal Adjustability

A multiple-pass optical platform eliminates essentially all optical alignment degrees of freedom, save one. A four-pass absorption spectrometer architecture is made rigid by firmly mounting dielectric-coated mirror prisms with no alignment capability to the platform. The laser diode beam is collimated by a small, custom-developed lens, which has only a rotational degree of freedom along the standard optical "z" axis. This degree is itself eliminated by adhesive after laser collimation. Only one degree of freedom is preserved by allowing the laser diode chip and mount subassembly to move relative to the collimating lens by using over-sized mounting holes. This allows full 360 deg motion of a few millimeters relative to the lens, which, due to the high numerical aperture of the lens, provides wide directional steering of the collimated laser beam.

Pilgrim, Jeffrey↗
NASA NTRS1987

Single-color laser ranging with a cube-corner-retroreflector array

Lidar cross section of some typical types of cube-corner retroreflectors (CCRs) having a three corner mirror system is investigated for the case that the CCR is tilted from the normal illumination axis. Analytic expressions for the effective aperture area for the two typical window types (circular and hexagonal) of CCRs are obtained for the case that the CCR is tilted. The range of incidence angle in which only the total reflection occurs at all three uncoated corner mirrors has been found to vary considerably with the orientation of CCR and the refractive index of the CCR prism. The analytical expression for the far-field diffraction pattern of a tilted CCR is obtained by taking different polarization transformation of the six sectors of the effective reflecting aperture into account. This expression is essential when evaluating the lidar cross section of a moving CCR which is tilted in general. Formulas for the angles defining the six sectors have also been obtained.

Song, G. Hugh↗