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At least 505 records · Page 28

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NASA NTRS1986

Wave-front correctors by diamond turning

The production of wave-front correctors by single-point diamond turning is reported. Interferograms are shown which demonstrate excellent agreement between the diamond-turned surface and the desired surface. It is concluded from this experiment that it is now feasible by means of single-point diamond turning to make generalized wave-front control surfaces or to produce any unusual surface desired by the optical designer. The maximum departure from the nearest regular surface is set by the dynamic range and maximum diamond point acceleration permitted by the machine.

Meinel, A. B.↗

NASA NTRS1987

Making Optical Correctors by Diamond Turning

Large Optics Diamond Turning Machine (LODTM) at Lawrence Livermore National Laboratory used to make highly amorphic reflecting wavefront-corrector plates with rms difference between desired and measured reflector surfaces of only 0.075 wave. Measured errors correspond to one standard deviation of uncertainties in digitization and reduction of interferograms of surface. Appears accuracy of LODTM-generated surface exceeds current ability to measure it. Work demonstrates feasibility of single-point diamond turning for manufacture of generalized wavefront-control surfaces or other unusual surfaces desired by optical designers.

Meinel, Aden B.↗

NASA NTRS1987

Edge detection - Image-plane versus digital processing

To optimize edge detection with the familiar Laplacian-of-Gaussian operator, it has become common to implement this operator with a large digital convolution mask followed by some interpolation of the processed data to determine the zero crossings that locate edges. It is generally recognized that this large mask causes substantial blurring of fine detail. It is shown that the spatial detail can be improved by a factor of about four with either the Wiener-Laplacian-of-Gaussian filter or an image-plane processor. The Wiener-Laplacian-of-Gaussian filter minimizes the image-gathering degradations if the scene statistics are at least approximately known and also serves as an interpolator to determine the desired zero crossings directly. The image-plane processor forms the Laplacian-of-Gaussian response by properly combining the optical design of the image-gathering system with a minimal three-by-three lateral-inhibitory processing mask. This approach, which is suggested by Marr's model of early processing in human vision, also reduces data processing by about two orders of magnitude and data transmission by up to an order of magnitude.

Huck, Friedrich O.↗

NASA NTRS1987

Broadband imaging system with three fields of view

Payload space limitations, high optical fidelity and the desirability of fast slew rates imply that certain broadband active pointing systems should be lightweight, compact and high performance with small moments of inertia. This paper describes a 12 inch diameter, F/5 reflective hybrid with two fields of view in the visible SWIR, and one field of view in the LWIR region. By incorporating two classic optical designs, these stringent requirements are met at a level as to assure reasonably attainable weight, size and performance estimates.

Manhart, Paul K.↗

NASA NTRS1987

The PMIRR optical system for Mars observer

The optical design of the pressure modulator infrared radiometer (PMIRR) is described. This limb and nadir scanning instrument will be used for remote sounding of the Martian atmosphere. To do this, the instrument has two pressure modulator cells and nine channels distributed over the wavelength range 0.3 to 50 microns.

Chrisp, Michael P.↗

NASA NTRS1988

Encircled energy correction method for raytrace programs

Program adjustments to increase the accuracy of the diffraction-based encircled energy analysis algorithms of the optical design computer programs ACCOS-V and SYNOPSYS are proposed. It is noted that the erroneous algorithms are based on the incorrect assumption that all the energy in a diffraction point spread function is contained within a circle of finite radius. Using these adjustments, more accurate encircled energy results are obtained for circles of radii less than or equal to the 100 percent boundary.

Dantzler, Andrew A.↗

NASA NTRS1989

A 58 x 62 pixel Si:Ga array camera for 5 - 14 micron astronomical imaging

A new infrared array camera system has been successfully applied to high background 5 - 14 micron astronomical imaging photometry observations, using a hybrid 58 x 62 pixel Si:Ga array detector. The off-axis reflective optical design incorporating a parabolic camera mirror, circular variable filter wheel, and cold aperture stop produces diffraction-limited images with negligible spatial distortion and minimum thermal background loading. The camera electronic system architecture is divided into three subsystems: (1) high-speed analog front end, including 2-channel preamp module, array address timing generator, bias power suppies, (2) two 16 bit, 3 microsec per conversion A/D converters interfaced to an arithmetic array processor, and (3) an LSI 11/73 camera control and data analysis computer. The background-limited observational noise performance of the camera at the NASA/IRTF telescope is NEFD (1 sigma) = 0.05 Jy/pixel min exp 1/2.

Gezari, D. Y.↗

NASA NTRS1989

Analysis of the 23 June 1988 flare using NIXT multilayer X-ray images

Results obtained during the June 23, 1988 flight of the normal incidence X-ray telescope (NIXT) sounding rocket payload are reported. The telescope primary is 25 cm in diameter, in a 750 cm e.f.l. (f/30) Ritchey-Chretien configuration, with multilayer coatings on the optics designed to image the Fe XVI and Mg X coronal emission lines near 63.5 A. Images of the onset phase of a large (M8) Solar flare were recorded during the flight on a modified T-max 400 film manufactured by Kodak. Some of the results obtained by comparison of the NIXT data with ground-based observations of the sun obtained simultaneously to the flight are also reported.

Golub, Leon↗

NASA NTRS1991

Three-component laser anemometer measurement systems

A brief overview of the different laser anemometer (LA) optical designs available is presented. Then, the LA techniques that can be used to design a three-component measurement system for annular geometries are described. Some of the facility design considerations unique to these LA systems are also addressed. Following this, the facilities and the LA systems that were used to successfully measure the three components of velocity in the blading of annular-flow machines are reviewed. Finally, possible LA system enhancements and future research directions are presented.

Goldman, Louis J.↗

NASA NTRS1990

Large-format electrographic and array detectors for a space Schmidt imaging telescope

Possible optical designs of imaging detectors for the spaceborne Schmidt telescope proposed by Carruthers et al. (1990) are discussed, surveying the currently or potentially available technology. Consideration is given to FUV electrographic detectors of large format (e.g., 120 mm with 10-micron resolution) using CsI photocathodes, the possible extension of the same technology to the mid-UV using Cs2Te instead of CsI, large CCD arrays for the visible and NIR, electron-bombarded CCDs for the FUV and mid-UV, and the data handling and processing requirements of these detectors.

Carruthers, George R.↗

NASA NTRS1991

Photomultiplier for optically probing Comet Halley

A low mass eight-color channel photopolarimeter was developed for the Giotto spacecraft. Utilizing the spin of the spacecraft, a multichannel plate photomultiplier, and a unique optical design, the instrument required no moving parts to measure color and linear polarization. The photopolarimeter collected data as the spacecraft passed through the coma of Comet Halley on March 13 and 14, 1986. This instrument's design, calibration, and reduction are discussed and some final results are presented.

Giovane, F.↗

NASA NTRS1992

A 5-18 micron array camera for high-background astronomical imaging

A new infrared array camera system using a Hughes/SBRC 58 x 62 pixel hybrid Si:Ga array detector has been successfully applied to high-background 5-18-micron astronomical imaging observations. The off-axis reflective optical system minimizes thermal background loading and produces diffraction-limited images with negligible spatial distortion. The noise equivalent flux density (NEFD) of the camera at 10 microns on the 3.0-m NASA/Infrared Telescope Facility with broadband interference filters and 0.26 arcsec pixel is NEFD = 0.01 Jy/sq rt min per pixel (1sigma), and it operates at a frame rate of 30 Hz with no compromise in observational efficiency. The electronic and optical design of the camera, its photometric characteristics, examples of observational results, and techniques for successful array imaging in a high- background astronomical application are discussed.

Gezari, Daniel Y.↗

NASA NTRS1991

Space astronomical telescopes and instruments; Proceedings of the Meeting, Orlando, FL, Apr. 1-4, 1991

The present volume on space astronomical telescopes and instruments discusses lessons from the HST, telescopes on the moon, future space missions, and mirror fabrication and active control. Attention is given to the in-flight performance of the Goddard high-resolution spectrograph of the HST, the initial performance of the high-speed photometer, results from HST fine-guidance sensors, and reconstruction of the HST mirror figure from out-of-focus stellar images. Topics addressed include system concepts for a large UV/optical/IR telescope on the moon, optical design considerations for next-generation space and lunar telescopes, the implications of lunar dust for astronomical observatories, and lunar liquid-mirror telescopes. Also discussed are space design considerations for the Space Infrared Telescope Facility, the Hubble extrasolar planet interferometer, Si:Ga focal-plane arrays for satellite and ground-based telescopes, microchannel-plate detectors for space-based astronomy, and a method for making ultralight primary mirrors.

Bely, Pierre Y.↗

NASA NTRS1991

A laser fluorescence anemometer system for the Langley 16- by 24-inch water tunnel

A laser fluorescence anemometer which comprises a three-component laser Doppler velocimeter system with a fourth channel to measure fluorescent dye concentration has been installed in the NASA Langley 16- by 24-in water tunnel. The system includes custom designed optics, data acquisition, and traverse control instruments and a custom software package. Feasibility studies demonstrated how water tunnels can be used in conjunction with advanced optical techniques to provide nonintrusive detailed flow field measurements of complex fluid flows with a minimum of expense. The measurements show that the laser fluorescence anemometer can provide new insight into the structure, entrainment, control and of mixing vortical and shear layer flows.

Owen, F. K.↗

NASA NTRS1993

Detection of Other Planetary Systems Using Photometry

Detection of extrasolar short-period planets, particularly if they are in the liquid-water zone, would be one of the most exciting discoveries of our lifetime. A well-planned space mission has the capability of making this discovery using the photometric method. An Earth-sized planet transiting a Sun-like star will cause a decrease in the apparent luminosity of the star by one part in 10,000 with a duration of about 12 hours and a period of about one year. Given a random orientation of orbital plane alignments with the line-of-sight to a star, and assuming our solar system to be typical, one would expect 1 percent of the stars monitored to exhibit planetary transits. A null result would also be significant and indicate that Earth-sized planets are rare. For the mission to be successful one needs a sensor system that can simultaneously monitor many thousands of stars with a photometric precision of one part in 30,000 per hour of integration. Confirmation of a detection will involve detection of a second transit that will yield a period and predict the time for a third and subsequent transits. The technology issues that need to be addressed are twofold: one is for an appropriate optical design; the other is for a detector system with the necessary photometric precision. Two candidates for the detector system are silicon diodes and CCD's.

Koch, D.↗

NASA NTRS1993

Development of a 9.3 micrometer CW LIDAR for the study of atmospheric aerosol

This report provides a brief summary of the basic requirements to obtain coherent or heterodyne mixing of the optical radiation backscattered by atmospheric aerosols with that from a fixed frequency source. The continuous wave (CW) mode of operation for a coherent lidar is reviewed along with the associated lidar transfer equation. A complete optical design of the three major subsystems of a CW, coherent lidar is given. Lens design software is implemented to model and optimize receiver performance. Techniques for the opto-mechanical assembly and some of the critical tolerances of the coherent lidar are provided along with preliminary tests of the subsystems. Included in these tests is a comparison of the experimental and the theoretical average power signal-to-noise ratio. The analog to digital software used to evaluate the power spectrum of the backscattered signal is presented in the Appendix of this report.

Whiteside, B. N.↗

NASA NTRS1990

The Hubble Space Telescope

The Hubble Space Telescope was launched from the Kennedy Space Center on April 24, 1990. Its initial check-out indicates that all sub-systems of the satellite are working very well, with two key exceptions: The line-of-sight pointing is subject to occasional jitter apparently induced by thermal stresses in the solar arrays; this is expected to be overcome. The telescope mirrors are found to contain approximately 0.5 wave rms of spherical aberration which cannot be overcome by any controls on board the satellite. This defect will limit the scientific performance of the telescope in the short run. However, the aberration can be fully corrected in the optical designs of future replacement instruments, and the delivery schedules of these instruments are being accelerated.

Boggess, Albert↗

NASA NTRS1991

Moderate Resolution Imaging Spectrometer-Tilt (MODIS-T) baseline concept

There will be several state of the art spectrometers in operation on the NASA Polar Orbiting Platform (NPOP-1) as part of the Earth Observing System (EOS). The Moderate Resolution Imaging Spectrometer (MODIS) will consist of two imaging spectroradiometric instruments, one nadir viewing (MODIS-N) and the other tiltable (MODIS-T) for ocean observation and land bidirectional reflectance studies. The Moderate Resolution Imaging Spectrometer-Tilt (MODIS-T) instrument is presently being constructed for flight on the EOS. It is an imaging spectrometer utilizing a grating type, reflecting Schmidt optical design that must provide a 1.1 kilometer spatial resolution at nadir from a spacecraft altitude of 705 kilometers with a 1500 kilometer cross-track swath and a +/- 50 degree forward and aft tilt capability. The instrument is required to cover the wavelength range from 400 to 880 nanometers in approximately 15 nanometer steps with less than 2.3 percent instrument induced polarization. The absolute radiometric accuracy must be at least 5 percent over the full dynamic range of the instrument.

Magner, Thomas J.↗