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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

Cross polarization in beam waveguide-fed Cassegrain reflector antennas

The sensitivity of the cross-polarization level to a deviation from the geometrical condition derived by Mizusawa and Kitsuregawa (1973) for different geometrical configurations is studied. This condition restricts the number of possible beam waveguide configurations for beam waveguide-fed Cassegrain reflector (BFCR) antennas. For a symmetrical feed, this condition results in a symmetrical aperture distribution with no cross-polarized component. By examining a number of beam waveguide configurations satisfying the condition, it was observed that for linearly polarized feed, the cross-polarization level is very sensitive to a deviation from this condition. For circularly polarized feed, deviation from this condition does not increase the cross-polarization level; however, it results in the squinting of the beam for BFCRs.

Houshmand, Bijan↗
NASA NTRS1968

Computer program for machine design of Cassegrain feed systems

Program designs the feed system geometry and the subreflector surface, with the main reflector configuration and frequency of operation as input data. Although the feedhorn is not designed, its required gain, beamwidth, and approximate radiation pattern are specified.

Potter, P. D.↗
NASA NTRS1991

A Cassegrain echelle spectrograph

The 'LPL echelle' is a CCD spectrograph with a resolving power of 160,000 and enough sensitivity to detect the brighter airglow emissions in a few minutes. It uses an R3.2 grating in a novel out-of-plane mounting that permits any wavelength to be placed on the blaze. A single order is selected by a medium-band interference filter. Lower dispersions and broader wavelength coverage are obtained by replacing the echelle by a 600 line/mm grating or a Littrow prism.

Hunten, D. M.↗
NASA NTRS1994

High-resolution imaging with a tip-tilt Cassegrain secondary

A prototype adaptive secondary mirror has been developed on a 2.3-m telescope to stabilize rapid motion caused by atmospheric turbulence. The instantaneous position of an image's centroid, or brightest speckle, is measured by a near-infrared camera system which enables the tip-tilt mirror to recenter the image. Correction is accomplished at closed-loop frequencies of less than or = 100 Hz on guide stars with K (2.2 micrometers) magnitudes less than or = 8. Image motion is reduced to less than 0.1 sec rms, removing over 90% of low-frequency (f less than or = 5 Hz) tilt power, leaving less than or = 1 rad exp 2 mean square wave front tilt phase error. In seeing conditions where D/r sub o approximately = 4, long exposures in the H band (1.6 micrometers) exhibit a nearly diffraction-limited resolution of 0.19 sec full width at half maximum (FWHM) (Strehl ratio aprroximately = 0.14)-a factor of 4 improvement over uncorrected images. Reduction of the present static optical errors will improve the Strehl ratio another factor of 2, leading to approximately 70% of the maximum possible Strehl ratio.

Close, L. M.↗
NASA NTRS1999

Design and Evaluation of a Telecompressor for a Cassegrain

In order to make better use of their telescope's available field for imaging, avid telescope users make use of an optical device known as a telecompressor also known as a Shapley lens or a focal reducer. Rather than widening the field like a Barlow lens by increasing the telescope's focal length a telecompressor does the opposite compressing the field by shortening the telescope's focal length. This allows for shorter exposure times for film and the potential to fit a telescope's entire field onto a CCD camera. A simple telecompressor would consist of a single positive lens. Such a system would be in adequate for astrophotography, which is why telecompressors like many other refractive optical systems are corrected for certain wavelengths of light. Sometimes a telescope can benefit from having the telecompressor designed just for that particular telescope. The director of the observatory at Texas A&M University Kingsville has been contemplating whether or not a custom made telecompressor would hold any benefits. The report discusses the preliminary design and evaluation of an astronomical achromat according to the third order aberration theory. The achromat is then optimized by finite ray-tracing. The achromat's performance as a telecompressor is compared to the performance of a telecompressor designed just for the telescope at TAMUK. The results indicate that the achromat performs about as well as the custom telecompressor. Analysis also presented that the custom telecompressor was optimized for the wrong system could potentially perform much better if it were optimized on the correct system. However in the meantime an ordinary achromat should suit the system well enough for CCD astroimaging.

Carden, Russell↗
NASA NTRS1997

MEASUREMENT OF THE NOISE IMPROVEMENT OF A 34-METER CASSEGRAIN ANTENNA RETROFITTED WITH A LOW-BACKSCATTERING STRUT

Large axially-symmetric ground-based dual-reflector antennas are used in a variety of applications simultaneously requiring very high gain and very low noise (e.g., satellite communications, radio astronomy, deep-space communications, and radar). In these systems, reducing the noise by 10 % is equivalent to increasing the antenna gain by roughly 0.5 dB. Since the early days of radio-astronomy this fact has continuously driven efforts to reduce the noise of front-end low-noise amplifiers--a major noise contributor. As the performance of the front-end amplifiers improved, the relative importance of the noise generated by the surrounding warm ground increased, causing the antenna noise to become a major factor in the overall system sensitivity. Since large ground-based reflectors have been around for several decades, the various electrical and mechanical parameters affecting their performance have received considerable attention and are generally well understood. However, the impact of the subreflector supporting struts on the antenna noise performance remains a source of uncertainty. The reason for this stems from the usually large electrical dimensions involved, which precludes the accurate modeling of the various strut-scattering mechanisms. For the particular antennas used on NASA's Deep Space Network, which have been designed to minimize all noise sources, several studies have typically reported measured noise temperatures between 2 and 3 K (at approx. 8.45 GHz, antenna pointing at zenith), attributed to the struts and other unknown effects (see for example [1] and [2]). With this in mind, an effort has recently been conducted to determine optimal strut shapes to reduce the associated noise contribution [3].

Prata, A., Jr.↗
NASA NTRS2016

Khayyam; Progress and Prospects of Coupling a Spatial Heterodyne Spectrometer (SHS) to a Cassegrain Telescope for Optical Interferometry

In the temporal study of faint, extended sources at high resolving power, Spatial Heterodyne Spectrometer (SHS) can offer significant advantages about conventional dispersive grating spectrometers. We describe here a four-year continuous progress in Mt. Hamilton, Lick Observatory, toward development of a prototype reflective Spacial Heterodyne Spectrometer, Khayyam, instrument-telescope configuration to combine all of the capabilities necessary to obtain high resolving power visible band spectra of diffuse targets from small aperture on-axis telescopes where significant observing time can be obtained. We will discuss the design considerations going into this new system, installation, testing of the interferometer-telescope combination, the technical challenges and procedures moving forward.

extended targets↗
NASA NTRSDate not supplied

Multipurpose Cassegrain System

Explore the source record for details and available documents.

solar sintering, space construction, space telesco↗
NASA NTRS1971

Comparison of various methods for mathematical analysis of the Foucault knife edge test pattern to determine optical imperfections

The linearized integral equation for the Foucault test of a solid mirror was solved by various methods: power series, Fourier series, collocation, iteration, and inversion integral. The case of the Cassegrain mirror was solved by a particular power series method, collocation, and inversion integral. The inversion integral method appears to be the best overall method for both the solid and Cassegrain mirrors. Certain particular types of power series and Fourier series are satisfactory for the Cassegrain mirror. Numerical integration of the nonlinear equation for selected surface imperfections showed that results start to deviate from those given by the linearized equation at a surface deviation of about 3 percent of the wavelength of light. Several possible procedures for calibrating and scaling the input data for the integral equation are described.

Gatewood, B. E.↗
NASA NTRS1984

The astrometry programme at Mt. John Observatory

The comet (and minor planet) astrometry program uses one of two 0.6 meter (24 in.) Cassegrain telescopes at Mt. John University Observatory. For astrometric photographs of comets and minor planets a simple guide probe camera is attached to the Cassegrain. Frequently the Cassegrain field does not include sufficient cataloged stars for a satisfactory reduction. In these cases the comet position is transferred to an astrograph plate. Ephemeris data are calculated to the tenth of a day nearest the meridian transit of the object or for dusk or dawn twilight for low objects. Star measurement and identification are checked by reducing positions of cataloged stars.

Gilmore, A. C.↗
NASA NTRS1984

Advanced wide-field broad-passband refracting field correctors for large telescopes

Design objectives, constraints, and optical data are presented for specific corrector designs under consideration for several large telescope projects. These include a preliminary 30-arcmin prime focus (f/2.0) refracting field corrector system for the University of California Ten-Meter Telescope (UC TMT); a compact 40-arcmin internal Cassegrain (f/1.75 hyperbola to f/5.0) broad-passband (3300 A to 1.0 micron) corrector suitable for imaging and multi-object spectroscopy at the UC TMT; three 60-arcmin Cassegrain correctors for 300-inch f/1.8 and f/2.0 parabolic primary mirrors suitable for a Fifteen-Meter NNTT/MMT; and a 300-inch 40-arcmin external Cassegrain (f/1.0 parabola to f/4.0) broad-passband (3300 A to 1.0 micron) corrector with ADC.

Epps, H. W.↗
NASA NTRS1990

Astronomical observations with normal incidence multilayer optics - Recent results and future prospects

High-resolution X-ray and EUV images of the solar corona have been obtained with two rocket-borne normal incidence Cassegrain multilayer telescopes. The Cassegrain images correspond to material at about 10 to the 6th K and about 80,000 K. Other images, at somewhat lower resolution, were obtained with Herschelian multilayer telescopes and Wolter-Schwarzschild hybrid grazing incidence/multilayer optical systems. The Cassegrain and Herschelian images are discussed emphasizing the analysis of polar plumes observed at the limb of the sun. The application of specific multilayer techniques to astronomical observations is discussed, emphasizing observations of the sun. Current efforts to develop a comprehensive Multi-Spectral Solar Telescope Array rocket instrument for the study of a wide variety of problems related to the solar atmosphere are reported.

Walker, Arthur B. C., Jr.↗
NASA NTRS2018

The NEID Precision Radial Velocity Spectrometer: Port Adapter Overview, Requirements, and Test Plan

The NEID spectrometer is an optical (380-930 nm), fiber-fed, precision Doppler spectrometer currently in development for the WIYN 3.5 m telescope at Kitt Peak National Observatory as part of the NN-EXPLORE partnership. Designed to achieve a radial velocity precision of < 30 cm/s, NEID will be sensitive enough to detect terrestrial-mass exoplanets around low-mass stars. Light from the target stars is focused by the telescope to a bent Cassegrain port at the edge of the primary mirror mechanical support. The specialized NEID "Port Adapter" system is mounted at this bent Cassegrain port and is responsible for delivering the incident light from the telescope to the NEID fibers. In order to provide stable, high-quality images to the science instrument, the Port Adapter houses several sub-components designed to acquire the target stars, correct for atmospheric dispersion, stabilize the light onto the science fibers, and calibrate the spectrometer by injecting known wavelength sources such as a laser frequency comb. Here we provide an overview of the overall opto-mechanical design and system requirements of the Port Adapter. We also describe the development of system error budgets and testplans to meet those requirements.

Cassegrain port↗
NASA NTRS1972

The spectrum of the quasi-stellar object PHL 957.

Spectra of the radio-quiet quasar PHL 957 were obtained at a 200-in. telescope with a Cassegrain image tube, a Cassegrain multichannel spectrometer, and an integrating television camera on the spectrograph. The image-tube spectra revealed 64 absorption lines between 3200 and 6800 A. The absolute energy distribution indicates that this quasar is one of the most luminous known. The absorption line redshifts and line profiles observed are discussed.

Lowrance, J. L.↗
NASA NTRS1974

Variable-beamwidth antennas

Two effective designs have been developed for Cassegrain and Gregorian antenna configurations. Each provides for both high-gain and low-gain operations. Cassegrain system sacrifices some efficiency due to small amount of increased spillover loss. Gregorian system provides for independent spillover control with two feeds.

Schmidt, R. F.↗
NASA NTRS1973

Bifocal dual reflector antenna

A bifocal dual reflector antenna is similar to and has better scan capability than classical cassegrain reflector antenna. The method used in determining the reflector surfaces is a modification of a design method for the dielectric bifocal lens. The three dimensional dual reflector is obtained by first designing an exact (in geometrical optics sense) two-point corrected two dimensional reflector and then rotating it around its axis of symmetry. A point by point technique is used in computing the reflector surfaces. Computed radiation characteristics of the dual reflector are compared with those of a cassegrain reflector. The results confirm that the bifocal antenna has superior performance.

Rao, B. L. J.↗