Search NASA⌕ Search

SEARCH · Search NASA

Results for “REFRACTING TELESCOPE”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS2007

High-Resolution, Wide-Field-of-View Scanning Telescope

A proposed telescope would afford high resolution over a narrow field of view (<0.10 ) while scanning over a total field of view nominally 16 wide without need to slew the entire massive telescope structure. The telescope design enables resolution of a 1-m-wide object in a 50- km-wide area of the surface of the Earth as part of a 200-km-wide area field of view monitored from an orbit at an altitude of 700 km. The conceptual design of this telescope could also be adapted to other applications both terrestrial and extraterrestrial in which there are requirements for telescopes that afford both wide- and narrow-field capabilities. In the proposed telescope, the scanning would be effected according to a principle similar to that of the Arecibo radio telescope, in which the primary mirror is stationary with respect to the ground and a receiver is moved across the focal surface of the primary mirror. The proposed telescope would comprise (1) a large spherical primary mirror that would afford high resolution over a narrow field of view and (2) a small displaceable optical relay segment that would be pivoted about the center of an aperture stop to effect the required scanning (see figure). Taken together, both comprise a scanning narrow-angle telescope that does not require slewing the telescope structure. In normal operation, the massive telescope structure would stare at a fixed location on the ground. The inner moveable relay optic would be pivoted to scan the narrower field of view over the wider one, making it possible to retain a fixed telescope orientation, while obtaining high-resolution images over multiple target areas during an interval of 3 to 4 minutes in the intended orbit. The pivoting relay segment of the narrow-angle telescope would include refractive and reflective optical elements, including two aspherical mirrors, to counteract the spherical aberration of the primary mirror. Overall, the combination of the primary mirror and the smaller relay optic would provide narrow-angle, diffraction-limited high resolution at a wavelength of 500 nm.

Sepulveda, Cesar↗
NASA NTRS1987

Wide-Angle, Flat-Field Telescope

All-reflective system unvignetted. Wide-angle telescope uses unobstructed reflecting elements to produce flat image. No refracting elements, no chromatic aberration, and telescope operates over spectral range from infrared to far ultraviolet. Telescope used with such image detectors as photographic firm, vidicons, and solid-state image arrays.

Hallam, K. L.↗
NASA NTRS2021

Baseline Optical Design for an Integrated Radio and Optical Communication System

This document outlines the baseline optical design for an Integrated Radio and Optical communication (iROC) system, specifically the version labeled in-house as Lunar R1.2a. The version number corresponds to the particular design iteration, including major and minor changes that have been made throughout the design process. The catadioptric design is based on a reflective Cassegrain telescope configuration united with refractive tertiary components in order to approach a diffraction limited, laser beam expander communication transmitter. The configuration presented is intended to be used as an optical transmitter only. Optical design parameters, far-field beam propagations, optical component sensitivity studies, and design explorations are included to provide a high-level understanding of the beam expander’s basic design requirements and optical performance.

optics↗
NASA NTRS1975

Properties of a silica aerogel Cerenkov radiator used in a cosmic ray telescope

A silica aerogel Cerenkov radiator with a refractive index of 1.06 has been flown in a balloon borne cosmic ray telescope. Clear separation of the elements in the iron group was achieved even at high energies. No detectable scintillation component was found. Some optical properties of the silica aerogel used in this flight are presented.

Cantin, M.↗
DOE OSTI2020

Updated design of the CMB polarization experiment satellite LiteBIRD

Recent developments of transition-edge sensors (TESs), based on extensive experience in ground-based experiments, have been making the sensor techniques mature enough for their application on future satellite CMB polarization experiments. LiteBIRD is in the most advanced phase among such future satellites, targeting its launch in Japanese Fiscal Year 2027 (2027FY) with JAXA's H3 rocket. It will accommodate more than 4000 TESs in focal planes of reflective low-frequency and refractive medium-and-high-frequency telescopes in order to detect a signature imprinted on the cosmic microwave background (CMB) by the primordial gravitational waves predicted in cosmic inflation. The total wide frequency coverage between 34GHz and 448GHz enables us to extract such weak spiral polarization patterns through the precise subtraction of our Galaxy's foreground emission by using spectral differences among CMB and foreground signals. Telescopes are cooled down to 5Kelvin for suppressing thermal noise and contain polarization modulators with transmissive half-wave plates at individual apertures for separating sky polarization signals from artificial polarization and for mitigating from instrumental 1/f noise. Passive cooling by using V-grooves supports active cooling with mechanical coolers as well as adiabatic demagnetization refrigerators. Sky observations from the second Sun-Earth Lagrangian point, L2, are planned for three years. An international collaboration between Japan, USA, Canada, and Europe is sharing various roles. In May 2019, the Institute of Space and Astronautical Science (ISAS), JAXA selected LiteBIRD as the strategic large mission No. 2.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1992

Useful receiver telescope diameter of ground-based and airborne 1-, 2-, and 10-micron coherent lidars in the presence of atmospheric refractive turbulence

Calculations of the integrated effect of atmospheric refractive turbulence on 1-, 2-, and 10-micron coherent lidar performance are presented for a series of different lidar propagation geometries. The effective lidar receiver telescope diameter is evaluated for each case. The results indicate that atmospheric turbulence should not be a significant factor in the performance of a downward-looking high-altitude or satellite-borne coherent lidar system. It is also shown that ground-based 1-2-micron coherent lidars may be limited in their useful telescope aperture, especially for horizontal or nearly horizontal path measurements near the ground.

Chan, Kin P.↗
NASA NTRS2005

High Accuracy, Absolute, Cryogenic Refractive Index Measurements of Infrared Lens Materials for JWST NIRCam using CHARMS

The current refractive optical design of the James Webb Space Telescope (JWST) Near Infrared Camera (NIRCam) uses three infrared materials in its lenses: LiF, BaF2, and ZnSe. In order to provide the instrument s optical designers with accurate, heretofore unavailable data for absolute refractive index based on actual cryogenic measurements, two prismatic samples of each material were measured using the cryogenic, high accuracy, refraction measuring system (CHARMS) at NASA GSFC, densely covering the temperature range from 15 to 320 K and wavelength range from 0.4 to 5.6 microns. Measurement methods are discussed and graphical and tabulated data for absolute refractive index, dispersion, and thermo-optic coefficient for these three materials are presented along with estimates of uncertainty. Coefficients for second order polynomial fits of measured index to temperature are provided for many wavelengths to allow accurate interpolation of index to other wavelengths and temperatures.

Leviton, Douglas↗
NASA NTRS2011

From X-Ray Telescopes to Neutron Focusing

In the case of neutrons the refractive index is slightly less than unity for most elements and their isotopes. Consequently, thermal and cold neutrons can be reflected from smooth surfaces at grazing-incidence angles. Hence, the optical technologies developed for x-ray astronomy can be applied for neutron focusing. The focusing capabilities of grazing incidence neutron imaging optics have been successfully demonstrated using nickel mirrors. The mirrors were fabricated using an electroformed nickel replication process at Marshall Space Flight Center. Results of the neutron optics experiments will be presented. Challenges of the neutron imaging optics as well as possible applications of the optics will be discussed.

Gubarev, M. V.↗
NASA NTRS2020

Design and Fabrication of Metamaterial Anti-reflection Coatings for the Simons Observatory

The Simons Observatory (SO) will be a cosmic microwave background (CMB) survey experiment with three small-aperture telescopes and one large-aperture telescope, which will observe from the Atacama Desert in Chile. In total, SO will field over 60,000 transition-edge sensor (TES) bolometers in six spectral bands centered between 27 and 280 GHz in order to achieve the sensitivity necessary to measure or constrain numerous cosmological quantities, as outlined in The Simons Observatory Collaboration et al. (2019). These telescopes require 33 highly transparent, large aperture, refracting optics. To this end, we developed mechanically robust, highly efficient, metamaterial anti-reflection (AR) coatings with octave bandwidth coverage for silicon optics up to 46 cm in diameter for the 22-55, 75-165, and 190-310 GHz bands. We detail the design, the manufacturing approach to fabricate the SO lenses, their performance, and possible extensions of metamaterial AR coatings to optical elements made of harder materials such as alumina.

Joseph E. Golec↗
NASA NTRS2004

The Cryogenic, High-Accuracy, Refraction Measuring System (CHARMS): A New Facility for Cryogenic Infrared through Vacuum Far-Ultraviolet Refractive Index Measurements

The optical designs of future NASA infrared (IR) missions and instruments, such as the James Webb Space Telescope's (JWST) Near-Mixed Camera (NIRCam), will rely on accurate knowledge of the index of refraction of various IR optical materials at cryogenic temperatures. To meet this need, we have developed a Cryogenic, High-Accuracy Refraction Measuring System (CHARMS). In this paper we discuss the completion of the design and construction of CHARMS as well as the engineering details that constrained the final design and hardware implementation. In addition, we will present our first light, cryogenic, IR index of refraction data for LiF, BaF2, and CaF2, and compare our results to previously published data for these materials.

Frey, Bradley J.↗
NASA NTRS1971

Seeing and scintillation

Astronomical telescopes image motion, distortion and scintillation, examining atmospheric refractive index and density/temperature variation effects

Young, A. T.↗
NASA NTRS1994

Infrared astronomy from the Moon

The purpose of this paper is to exhibit the advantages and limitations to infrared astronomical observations form the moon. The most obvious apparent advantage is the lack of a lunar atmosphere; radiation arriving from the universe is neither extinguished nor refracted as it approaches the lunar surface. However, the Earth's atmosphere's protection against cosmic rays is also lost, and infrared detectors are highly sensitive to irradiation by energetic particles. A second apparent advantage is the relative ease with which beams from an array of telescopes can be interferometrically combined; again the vacuum environment with constant refractive index of unity throughout, permits combination without phase delay across the entire spectral range. But thermal radiation from optical components and stray radiation from the lunar environment, just outside the light path, tend to lessen that advantage, except in narrow-spectral-band spatial interferometry, in which only the radiation in individual spectral lines is mapped, and broad-band thermal emission can be effectively filtered out. On the Moon's night side, and in polar craters on the Moon, radiative cooling should permit the attainment of high sensitivity with large telescopes. Just as the proposed Edison spacecraft primary mirror is expected to reach temperatures around 40 K, so also large lunar primary mirrors might be expected to reach temperatures in that range, making the zodiacal glow the main source of noise at wavelengths shortward of 25 micrometers. The slow rota tion of the Moon, and the lack of vibrations from natural sources such as winds, should provide advantages in guiding on specific astronomical sources. To learn as much as possible about the difficulties of remote observations in a hostile environment, Antarctic observatories should be used as test beds for the rigors of lunar observations. The strenuous requirements for successful astronomical observations from the South Pole are similar to those expected to be encountered in observations conducted from the Moon.

Harwit, Martin↗
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 NTRS1998

Very High-Resolution Space Telescope Using the Earth Atmosphere as the Objective Lens

Telescopes are critical elements of NASA's space program. Very high resolution telescopes are needed to study planets of neighboring stellar systems and life beyond earth. The Earth's atmosphere refracts sunlight such that the sun's image appears about a half degree above its real position during sunset. If we could build a space telescope using the Earth's atmosphere as an objective lens the aperture of such a space telescope would be the diameter of the earth.

space↗
NASA NTRS1977

Laser probe for measuring 2-D wave slope spectra of ocean capillary waves

A laser-optical instrument for use in determining the two-dimensional wave-slope spectrum of ocean capillary waves is described. The instrument measures up to a 35-deg tip angle of the surface normal by measuring the position of a refracted laser beam directed vertically upward through a water surface. A telescope, a continuous two-dimensional Schottky barrier photodiode, and a pair of analog dividers render the signals independent of water height and insensitive to laser-beam intensity fluctuations. Calibration is performed entirely in the laboratory before field use. Sample records and wave-slope spectra are shown for one-dimensional wave-tank tests and for two-dimensional ocean tests. These are presented along with comparison spectra for calm and choppy water conditions. A mechanical wave follower was used to adjust the instrument position in the presence of large ocean swell and tides.

Palm, C. S.↗
NASA NTRS1993

Suppressing Spurious Reflections In An Interferometer

Dynamic-aperture fringe discriminator is simple device enhancing operation of interferometer of spherical-wave-front type used to test lenses, telescopes, and other optical instruments. Device suppresses reflections from surfaces of refractive optical elements in instrument and/or test setup. Reflections from refractive optical components eliminated by blocking half of interferometer aperture.

Steimle, Lawrence J.↗
NASA NTRS1990

Design of a shuttle-based space debris telescope

A 1.6-meter diameter f/0.95 all-reflecting telescope was designed to observe orbital debris particles as small as 1 mm from the shuttle payload bay. The telescope was specified to have a flat focal surface without the imposition of refractive elements. Two design configurations involving three mirrors were evaluated - a reflective Schmidt-Cassegrain and a modified Paul corrector. The Paul system was found to be more compact and appropriate for this application.

Richardson, E. H.↗
NASA NTRS1993

Diffractive optical elements for generating arbitrary line foci

The key optical component in the architecture of the linearly variable magnification telescope presented here is a conical lens. This architecture has application to Doppler radar processing and to wavelet processing. Unfortunately, the unique surface profile of a conical lens does not allow traditional grinding techniques to be used for fabrication; therefore, its fabrication is considered custom. In addition to the requirement of custom fabrication, a refractive conical lens introduces phase aberrations that are intrinsic to its conic shape. Further, due to the large prismatic component of the lens, the variable magnification telescope architecture is off-axis. To overcome the fabrication and application difficulties of a refractive lens, we consider the construction of a hybrid diffractive-refractive lens.

Mait, Joseph N.↗