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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 NTRS1973

Evaluation of the electro-optic direction sensor

Evaluation of a no-moving-parts single-axis star tracker called an electro-optic direction sensor (EODS) concept is described and the results are given in detail. The work involved experimental evaluation of a breadboard sensor yielding results which would permit design of a prototype sensor for a specific application. The laboratory work included evaluation of the noise equivalent input angle of the sensor, demonstration of a technique for producing an acquisition signal, constraints on the useful field-of-view, and a qualitative evaluation of the effects of stray light. In addition, the potential of the silicon avalanche-type photodiode for this application was investigated. No benefit in noise figure was found, but the easily adjustable gain of the avalanche device was useful. The use of mechanical tuning of the modulating element to reduce voltage requirements was also explored. The predicted performance of EODS in both photomultiplier and solid state detector configurations was compared to an existing state-of-the-art star tracker.

Johnson, A. R.↗
NASA NTRS1973

An electron-lens for opaque photocathodes.

It is possible to employ opaque photocathodes in image tubes having a special electromagnetic lens without the use of special internal image-forming optical lenses or mirrors. The special electron lens, having flat object and image planes, is found to provide excellent quality electron-optical image transfer. Stray light reflection inside the tube is expected to be less serious in this electron lens than in a conventional magnetically focused image tube lens due to the offset image plane, and due to the increased absorption of photons in opaque photocathode applications.

Johnson, C. B.↗
NASA NTRS1975

Angular device for optical filters

Device provides a means for precise angular adjustment of optical filters in Raman calibration detector units. Device prevents stray light from entering system and has the capability of repeated alignments to predetermined angles.

Overbay, L. W.↗
NASA NTRS1975

The effects of out-of-field radiation on earth-observing telescopes

The stray radiation rejection requirements for the Synchronous Earth Observation Satellite telescope were determined and compared with estimated stray radiation rejection performance. It was found that normal baffle design practice and 0.05 wavelength rms surface roughness on the mirrors is adequate to prevent stray light from limiting the telescope measurements as long as the sun is 10 deg or more from the edge of the field of view for a baffle tube length-to-aperture diameter ratio of 6.

Young, P. J.↗
NASA NTRS1975

Optical design of the SBUV/TOMS experiment on Nimbus G

The paper examines the tradeoffs performed in optimizing the optical design of the solar backscatter ultraviolet/total ozone mapping spectrometer (SBUV/TOMS) experiment on Nimbus G to stringent performance requirements within the limitations of the spacecraft interface. The SBUV portion of the experiment incorporates a double monochromator optimized for better than 1.0 A spectral resolution over the wavelength range 1600-4000 A. The TOMS portion of the experiment is a stepped line scanning system with a 105-deg total field of view. Special techniques are used to reduce the polarization sensitivity of the instrument to less than 5% for 100% linearly polarized incident radiation and to keep the spectral stray light to less than 0.000001 of the incident solar spectrum. Optical material selection is imperative in order to minimize the effects of fluorescence and phosphorescence arising from the bombardment of particulate radiation in space.

Henderson, B. D.↗
NASA NTRS1977

Optical proximity detector

Sensitive, relatively inexpensive instrument uses phase-detection techniques to sense presence of objects. Phase-sensitive detectors, LED, photodiode with response matched to LED output, and filtering lens allow detector to operate over narrow radiation band, giving selectivity over stray light.

Hermann, W. A.↗
NASA NTRS1977

Anastigmatic three-mirror telescope

Proposed three-mirror telescope provides high resolution over flat image field of 1.5 degrees. Telescope also suppresses stray-light without elaborate baffling system, making it well suited for space astronomy and other high performance and low-light level applications.

Korsch, D.↗
NASA NTRS1978

Diffuse-direct ultraviolet ratios with a compact double monochromator

An improved system has been implemented for measuring the ratio of the diffuse skylight to the direct sunlight in the biologically active region of the UV near the atmospheric limit. It combines a double monochromator employing holographic gratings for reduction of stray light with a cooled photomultiplier tube to provide a greatly improved SNR below 300 nm. Data may be obtained in either a scan mode or a narrowband photometry mode; in the latter mode accurate ratios have been obtained near 290 nm. Representative data are discussed along with a theoretical model of the ratio. The system is compact enough for use in a mobile monitoring system.

Garrison, L. M.↗
NASA NTRS1979

The application of laser Rayleigh scattering to gas density measurements in hypersonic helium flows

Measurements of the mean static free-stream gas density have been made in two Langley Research Center helium facilities, the 3-inch leg of the high-Reynolds-number helium complex and the 22-inch hypersonic helium tunnel. Rayleigh scattering of a CW argon ion laser beam at 514.5 nm provided the basic physical mechanism. The behavior of the scattered signal was linear, confirmed by a preliminary laboratory study. That study also revealed the need to introduce baffles to reduce stray light. A relatively simple optical system and associated photon-counting electronics were utilized to obtain data for densities from 10 to the 23rd to 10 to the 25th per cu m. The major purpose, to confirm the applicability of this technique in the hypersonic helium flow, was accomplished.

Hoppe, J. C.↗
NASA NTRS1979

On-orbit control system performance of the HEAO-2 observatory

The on-orbit performance of the High Energy Astronomy Observatory is described. The control system utilizes precision gyros for attitude reference and skewed reaction wheels controlled by a reprogrammable computer. The observatory points at selected targets, maneuvers automatically and acquires guide stars for updating at each target. Performance data indicates maneuver accuracies less than one arc minute and pointing accuracies of 2-5 arc seconds. Use of 7th-9th magnitude guide stars has resulted in several improper updates caused by 'flat-field' stray light effects in the star trackers. The method used to discriminate true stars from the flat-field is also presented.

Rose, R. E.↗
NASA NTRS1979

Report of Optical Radiometric Instruments and Calibration Panel

Measurement and accuracy needs for remote sensing are analyzed. Topics discussed include: (1) in orbit performance degradation due to contamination; (2) increased radiometric accuracy required for detecting small changes over long periods of time in environmental parameters; (3) references for verifying calibration in orbit; (4) high attenuation neutral density filters; (5) the sun as a radiation source for testing; (6) rejection of stray light; (7) development of spectrally flat detectors for flight sensors; and (8) long term stability of sensor components.

Source record↗
NASA NTRS1979

The space telescope observatory

A guide to the expected characteristics of the space telescope (ST) observatory is presented. The general objectives of the ST observatory are summarized. The plans for the development of the observatory are described with a brief history of the scientific activities; an account of the scope of the present program; a summary of the major responsibilities of the contractors; and a list of the project milestones are included. The performance characteristics of the observatory are provided including the imaging and stray light characteristics, pointing capability, and operational access. The expected performance characteristics of all six of the first generation science instruments are summarized. The mode of operations is described which includes a discussion of program options, guide star selection, methods of acquisition, and quick look data capabilities.

Bahcall, J. N.↗
NASA NTRS1979

Narrow-field radiometry in a quasi-isotropic atmosphere

If a radiometer having a narrow field of view is used to measure the radiance of a source such as a quasi-isotropic atmosphere, a knowledge of the out-of-field responsivity is critical. For example, if a radiometer with a field of view of 5 deg (full-angle) has a relative responsivity of 0.0001 for the out-of-field radiation, the contribution of the out-of-field radiation (assuming an isotropic source subtending 2 steradians) is 10.5% of the total signal. Either the stray light suppression of the radiometer must be extremely high or methods of determining the out-of-field response must be developed. A description of one method of determining the effect of out-of-field response and its application to a planetary atmospheric radiometer is presented.

Holmes, A.↗
NASA NTRS1980

Velocity measurements by laser resonance fluorescence

The photonburst correlation method was used to detect single atoms in a buffer gas. Real time flow velocity measurements with laser induced resonance fluorescence from single or multiple atoms was demonstrated and this method was investigated as a tool for wind tunnel flow measurement. Investigations show that single atoms and their real time diffusional motion on a buffer gas can be measured by resonance fluorescence. By averaging over many atoms, flow velocities up to 88 m/s were measured in a time of 0.5 sec. It is expected that higher flow speeds can be measured and that the measurement time can be reduced by a factor of 10 or more by careful experimental design. The method is clearly not ready for incorporation in high speed wind tunnels because it is not yet known whether the stray light level will be higher or lower, and it is not known what detection efficiency can be obtained in a wind tunnel situation.

She, C. Y.↗
NASA NTRS1978

Infrared Astronomical Satellite (IRAS) analysis, introduction

Stray light transmittance analysis on a design of the Infrared Astronomical Satellite (IRAS) is presented. The system was evaluated for scattered radiation propagation with the use of the APART (Arizon's Paraxial Analysis of Radiation Transfer), and the propagation of diffracted energy with both PADE (Paraxial Analysis of Diffracted Energy) and the GUERAP II programs. The scattered radiation analysis was performed by using both a 5% diffuse black on the baffle and vane surfaces and by using a mathematical model of the Martin Black scattering characteristics. The sources of infrared radiation and of radiation in the visible wavelengths are identified. Diffraction effects are dominant only at the large off-axis angles, except for a few specific cases and smaller angles. At the longer wavelengths the diffraction contributions go up significantly. It is the comparative increase which determines which propagation process predominates. Combined transmittance values are presented.

Source record↗
NASA NTRS1981

Space Telescope orbital viewing constraints

Astronomical observations with the Space Telescope will be constrained by spacecraft operational requirements and capabilities, orbital viewing conditions, and the space environment. While ultraviolet or bright visual-range observations may be performed for 53 to 94.6 minutes per orbit (from a 500 kilometer altitude), certain stray light sensitive experiments may be limited to 0-48 minutes of viewing per orbit. Careful operations planning may make possible observations of 'secondary' targets while a primary target is occulted, of objects as close as 18 deg to the sun, or of objects visible when the spacecraft is in a high radiation environment.

Sherrill, T. J.↗
NASA NTRS1981

Particle contamination from Martin Optical Black

The design of the barrel baffle of the Infrared Astronomical Satellite (IRAS) Optical Subsystem to minimize production of particulate contamination is described. The configuration of the 50-inch long, 28.5-inch diameter baffle required pop-rivet assembly after coating with Martin Optical Black for stray light suppression. An experiment to determine the contamination produced at assembly led to the modification of the baffle construction to preclude such damage to the coated surfaces.

Young, P. J.↗