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NASA NTRS1990

Dispersive spectroscopy on AXAF

The designs of two transmission grating spectrometers and a Bragg crystal spectrometer that are being developed for the Advanced X-ray Astrophysics Facility (AXAF) are described. The gratings, which are composed of arrays of small facets mounted on plates which can be inserted immediately behind the AXAF telescope, divide the AXAF energy band (80 eV-10 keV) into three regions and attain very high resolving powers for point sources. The Bragg Crystal Spectrometer (BCS) is a focal plane instrument, in which X-rays that satisfy the Bragg law are reflected from a curved crystal which refocuses the beam onto an imaging detector. The BCS achieves the highest spectral resolutions of the AXAF spectrometers: for E values between 500 and 1600 eV, the FWHM of a narrow line is less than 1 eV.

Markert, T. H.↗

NASA NTRS2006

Theodolite Ring Lights

Theodolite ring lights have been invented to ease a difficulty encountered in the well-established optical-metrology practice of using highly reflective spherical tooling balls as position references. A theodolite ring light produces a more easily visible reflection and eliminates the need for an autocollimating device. A theodolite ring light is a very bright light source that is well centered on the optical axis of the instrument. It can be fabricated, easily and inexpensively, for use on a theodolite or telescope of any diameter.

Clark, David↗

NASA NTRS2016

Shrink Tape Technique for Heat Forming Aluminum Substrates for Thin Foil X-Ray Mirrors and the Neutron Star Interior Composition Explorer X-Ray Concentrators

Consistent improvements in the design and fabrication of thin-foil, epoxy-replicated x-ray mirrors for astronomical telescopes have yielded increasingly higher quality and more precise astrophysical data. The Neutron Star Interior Composition Explorer (NICER) x-ray timing mission optics continues this tradition and introduces design elements that promise even more accurate measurements and precise astrophysical parameters. The singly reflecting concentrators have a curved axial profile to improve photon concentration and a sturdy full shell structure for enhanced module stability. These design elements introduced the challenge of reliably forming mirror substrates at an acceptable production rate. By developing a technique using heat shrink tape to compress and conform thin aluminum mirror substrates to shaping mandrels, production rate improved with successful fabrication. The technique's efficiency was analyzed by measuring hundreds of substrate profiles postforming, performance testing completely assembled concentrators composed of every size substrate, and comparing the results to simulated fabrication scenarios. On average, the profiles were copied within 4.6 plus or minus 3.7 percent. These measurements and the overall success of NICER's optics, via ground calibration, have shown that the heat-shrink tape method is reliable, repeatable, and could be used in future missions to increase production rate and improve performance.

Balsamo, Erin↗

NASA NTRS1993

Telescope for x ray and gamma ray studies in astrophysics

Imaging of x-rays has been achieved by various methods in astrophysics, nuclear physics, medicine, and material science. A new method for imaging x-ray and gamma-ray sources avoids the limitations of previously used imaging devices. Images are formed in optical wavelengths by using mirrors or lenses to reflect and refract the incoming photons. High energy x-ray and gamma-ray photons cannot be reflected except at grazing angles and pass through lenses without being refracted. Therefore, different methods must be used to image x-ray and gamma-ray sources. Techniques using total absorption, or shadow casting, can provide images in x-rays and gamma-rays. This new method uses a coder made of a pair of Fresnel zone plates and a detector consisting of a matrix of CsI scintillators and photodiodes. The Fresnel zone plates produce Moire patterns when illuminated by an off-axis source. These Moire patterns are deconvolved using a stepped sine wave fitting or an inverse Fourier transform. This type of coder provides the capability of an instantaneous image with sub-arcminute resolution while using a detector with only a coarse position-sensitivity. A matrix of the CsI/photodiode detector elements provides the necessary coarse position-sensitivity. The CsI/photodiode detector also allows good energy resolution. This imaging system provides advantages over previously used imaging devices in both performance and efficiency.

Weaver, W. D.↗

NASA NTRS1991

Multi-Spectral Solar Telescope Array. IV - The soft X-ray and extreme ultraviolet filters

NASA's Multi-Spectral Solar Telescope Array uses various combinations of thin foil filters composed of Al, C, Te, Be, Mo, Rh, and phthalocyanine to achieve the requisite radiation-rejection characteristics. Such rejection is demanded by the presence of strong EUV radiation at longer wavelengths where the specular reflectivity of multilayer mirrors can cause 'contamination' of the image in the narrow band defined by the Bragg condition.

Lindblom, Joakim F.↗

NASA NTRS1991

Diagnosing the optical state of the Hubble Space Telescope

Problems involved in the diagnosing the optical status of the Hubble Space Telescope (HST) are reviewed with emphasis on the task of determining the actual hyperboloidal shape of the primary mirror. Based on the results of several studies, a revised value of K = -1.0139 (an average of the best estimates derived from the analysis of the reflective null corrector and no-orbit star images) was recommended as the best value for the design of the second-generation Wide Field and Planetary Camera so as to restore the imaging ability of the HST to its original specification.

Vaughan, Arthur H.↗

NASA NTRS1992

Multilayer and grazing incidence X-ray/EUV optics; Proceedings of the Meeting, San Diego, CA, July 22-24, 1991

The present conference discusses the Advanced X-ray Astrophysics Facility (AXAF) calibration by means of synchrotron radiation and its X-ray reflectivity, X-ray scattering measurements from thin-foil X-ray mirrors, lobster-eye X-ray optics using microchannel plates, space-based interferometry at EUV and soft X-ray wavelengths, a water-window imaging X-ray telescope, a graded d-spacing multilayer telescope for high energy X-ray astronomy, photographic films for the multispectral solar telescope array, a soft X-ray ion chamber, and the development of hard X-ray optics. Also discussed are X-ray spectroscopy with multilayered optics, a slit aperture for monitoring X-ray experiments, an objective double-crystal spectrometer, a Ly-alpha coronagraph/polarimeter, tungsten/boron nitride multilayers for XUV optical applications, the evaluation of reflectors for soft X-ray optics, the manufacture of elastically bent crystals and multilayer mirrors, and selective photodevices for the VUV.

Hoover, Richard B.↗

NASA NTRS1998

Increased Capabilities for Conventional Lidars using Holographic Optics

While the field of holographic optics is relatively new, and numerous applications are still being devised and tested, there are good prospects that the use of holographic optical elements (HOEs) may revolutionize the design and applications of optical systems in various fields. This paper is not a review of HOE developments, but rather an account of a particular application, namely the extension of the scanning capabilities of conventional telescopes-in particular, lidar receivers-by means of special holographic accessories. As originally described and in a patent, and in several subsequent publications the HOE lidar was based on the concept of building into the holographic element (either a transmitting one or a reflecting one) all the optical power needed to focus a lidar return to a detector at the HOE's focal point, as well as subjecting the lidar return to both angular deflection and wavelength selection. Results will be reported on the use of Holographic Transmission Gratings (HTGs) at 532 nm and 770 nm at 45 deg. cone angle, both in the laboratory and in the atmosphere at Utah State University.

Wilkerson, Thomas D.↗

NASA NTRS2023

Sidelobe Modeling and Mitigation for A Three Mirror Anastigmat Cosmic Microwave Background Telescope

Telescopes measuring cosmic microwave background (CMB) polarization on large angular scales require exquisite control of systematic errors to ensure the fidelity of the cosmological results. In particular, far-sidelobe contamination from wide angle scattering is a potentially prominent source of systematic error for large aperture microwave telescopes. Here we describe and demonstrate a ray-tracing-based modeling technique to predict far sidelobes for a three mirror anastigmat telescope designed to observe the CMB from the South Pole. Those sidelobes are produced by light scattered in the receiver optics subsequently interacting with the walls of the surrounding telescope enclosure. After comparing simulated sidelobe maps and angular power spectra for different enclosure wall treatments, we propose a highly scattering surface that would provide more than an order of magnitude reduction in the degree-scale far-sidelobe contrast compared to a typical reflective surface. We conclude by discussing the fabrication of a prototype scattering wall panel and presenting measurements of its angular scattering profile.

Ian Gullett↗

NASA NTRS1998

The Laser Vegetation Imaging Sensor (LVIS): An Airborne Laser Altimeter for Mapping Vegetation and Topography

The Laser Vegetation Imaging Sensor (LVIS) is an airborne laser altimeter designed to quickly and extensively map surface topography as well as the relative heights of other reflecting surfaces within the laser footprint. Since 1997, this instrument has primarily been used as the airborne simulator for the Vegetation Canopy Lidar (VCL) mission, a spaceborne mission designed to measure tree height, vertical structure and ground topography (including sub-canopy topography). LVIS is capable of operating from 500 m to 10 km above ground level with footprint sizes from 1 to 60 m. Laser footprints can be randomly spaced within the 7 degree telescope field-of-view, constrained only by the operating frequency of the ND:YAG Q-switched laser (500 Hz). A significant innovation of the LVIS altimeter is that all ranging, waveform recording, and range gating are performed using a single digitizer, clock base, and detector. A portion of the outgoing laser pulse is fiber-optically fed into the detector used to collect the return signal and this entire time history of the outgoing and return pulses is digitized at 500 Msamp/sec. The ground return is then located using software digital signal processing, even in the presence of visibly opaque clouds. The surface height distribution of all reflecting surfaces within the laser footprint can be determined, for example, tree height and ground elevation. To date, the LVIS system has been used to monitor topographic change at Long Valley caldera, CA, as part of NASA's Topography and Surface Change program, and to map tree structure and sub-canopy topography at the La Selva Biological Research Station in Costa Rica, as part of the pre-launch calibration activities for the VCL mission. We present results that show the laser altimeter consistently and accurately maps surface topography, including sub-canopy topography, and vegetation height and structure. These results confirm the measurement concept of VCL and highlight the benefits of airborne prototypes of spaceborne instruments.

Bryan, J.↗

DOE OSTI2023

Sidelobe modeling and mitigation for a three mirror anastigmat cosmic microwave background telescope

Telescopes measuring cosmic microwave background (CMB) polarization on large angular scales require exquisite control of systematic errors to ensure the fidelity of the cosmological results. In particular, far-sidelobe contamination from wide angle scattering is a potentially prominent source of systematic error for large aperture microwave telescopes. Here we describe and demonstrate a ray-tracing-based modeling technique to predict far sidelobes for a three mirror anastigmat telescope designed to observe the CMB from the South Pole. Those sidelobes are produced by light scattered in the receiver optics subsequently interacting with the walls of the surrounding telescope enclosure. After comparing simulated sidelobe maps and angular power spectra for different enclosure wall treatments, we propose a highly scattering surface that would provide more than an order of magnitude reduction in the degree-scale far-sidelobe contrast compared to a typical reflective surface. Finally, we conclude by discussing the fabrication of a prototype scattering wall panel and presenting measurements of its angular scattering profile.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

NASA NTRS1967

Cone and column solar energy concentrator

Solar energy concentrator consists of a reflective membrane cone and a stepped parabolic column located along the optical axis of the cone. The membrane cone can be folded for packaging and is supported by an expandable ring at the rim of the cone when erected. The stepped parabolic column can be telescoped for packaging.

Mc Cusker, T. J.↗

NASA NTRS1981

Four-cell solar tracker

Forty cm Sun tracker, consisting of optical telescope and four solar cells, stays pointed at Sun throughout day for maximum energy collection. Each solar cell generates voltage proportional to part of solar image it receives; voltages drive servomotors that keep image centered. Mirrored portion of cylinder extends acquisition angle of device by reflecting Sun image back onto solar cells.

Berdahl, C. M.↗

NASA NTRS1986

Surface control system for the 15 meter hoop-column antenna

The 15-meter hoop-column antenna fabricated by the Harris Corporation under contract to the NASA Langley Research Center is described. The antenna is a deployable and restowable structure consisting of a central telescoping column, a 15-meter-diameter folding hoop, and a mesh reflector surface. The hoop is supported and positioned by 48 quartz cords attached to the column above the hoop, and by 24 graphite cords from the base of the antenna column. The RF reflective surface is a gold plated molybdenum wire mesh supported on a graphite cord truss structure which is attached between the hoop and the column. The surface contour is controlled by 96 graphite cords from the antenna base to the rear of the truss assembly. The antenna is actually a quadaperture reflector with each quadrant of the surface mesh shaped to produce an offset parabolic reflector. Results of near-field and structural tests are given. Controls structures and electromagnetics interaction, surface control system requirements, mesh control adjustment, surface control system actuator assembly, surface control system electronics, the system interface unit, and control stations are discussed.

Miller, James B.↗

NASA NTRS1997

Mineralogy of the Martian Surface: Crustal Composition to Surface Processes

The main results have been published in the refereed literature, and thus this report serves mainly to summarize the main findings and indicate where the detailed papers may be found. Reflectance spectroscopy has been an important tool for determining the mineralogic makeup of the near surface materials on Mars. Analysis of the spectral properties of the surface have demonstrated that these attributes are heterogeneous from the coarse spatial but high spectral resolution spectra obtained with telescopes to the high spatial but coarse spectral resolution Viking data (e.g. Arvidson et al., 1989; McEwen et al., 1989). Low albedo materials show strong evidence for the presence of igneous rock forming minerals while bright materials are generally interpreted as representing heavily altered crustal material. How these materials are physically and genetically related has important implications for understanding martian surface properties and processes, weathering histories and paths, and crustal composition. The goal of this research is to characterize the physical and chemical properties of low albedo materials on Mars and the relationship to intermediate and high albedo materials. Fundamental science questions to be pursued include: (1) the observed distributions of soil, rock, and dust a function of physical processes or weathering and (2) different stages of chemical and physical alteration fresh rock identified. These objectives will be addressed through detailed analyses and modelling of the ISM data from the Phobos-2 mission with corroborating evidence of surface composition and properties provided by data from the Viking mission.

Mustard, John F.↗

NASA NTRS2012

Airborne Measurements of Atmospheric Pressure made Using an IPDA Lidar Operating in the Oxygen A-Band

We report airborne measurements of atmospheric pressure made using an integrated path differential absorption (IPDA) lidar that operates in the oxygen A-band near 765 nm. Remote measurements of atmospheric temperature and pressure are needed for NASA s Active Sensing of CO2 Emissions Over Nights, Days, and Seasons (ASCENDS) mission to measure atmospheric CO2. Accurate measurements of tropospheric CO2 on a global scale are very important in order to better understand its sources and sinks and to improve our predictions of climate change. The goal of ASCENDS is to determine the CO2 dry mixing ratio with lidar measurements from space at a level of ~1 ppm. Analysis to date shows that with current weather models, measurements of both the CO2 column density and the column density of dry air are needed. Since O2 is a stable molecule that uniformly mixed in the atmosphere, measuring O2 absorption in the atmosphere can be used to infer the dry air density. We have developed an airborne (IPDA) lidar for Oxygen, with support from the NASA ESTO IIP program. Our lidar uses DFB-based seed laser diodes, a pulsed modulator, a fiber laser amplifier, and a non-linear crystal to generate wavelength tunable 765 nm laser pulses with a few uJ/pulse energy. The laser pulse rate is 10 KHz, and average transmitted laser power is ~20 mW. Our lidar steps laser pulses across a selected line O2 doublet near 764.7 nm in the Oxygen A-band. The direct detection lidar receiver uses a 20 cm diameter telescope, a Si APD detector in Geiger mode, and a multi-channel scalar to detect and record the time resolved laser backscatter in 40 separate wavelength channels. Subsequent analysis is used to estimate the transmission line shape of the doublet for the laser pulses reflected from the ground. Ground based data analysis allows averaging from 1 to 60 seconds to increase SNR in the transmission line shape of the doublet. Our retrieval algorithm fits the expected O2 lineshapes against the measurements and determines the atmospheric pressure by minimizing the error between the observations and model. We first demonstrated our airborne lidar during flights during summer 2010. We made several improvements and made measurements during the Ascends flights during July 2011. More information about the technique, lidar instrument, airborne measurements, and pressure estimates will be described in the presentation.

Riris, Haris↗

NASA NTRS2018

The Aeolus Mission Concept, an Innovative Mission to Study the Winds and Climate of Mars

Aeolus is a mission to provide the first set of global, seasonal, and diurnal data to characterize winds and study the climate of Mars. Aeolus measures surface and atmospheric temperatures, aerosol abundances, and Doppler shifts in atmospheric spectral lines. The payload includes a system of four of a new type of miniaturized Spatial Heterodyne Spectrometer (SHS) paired to two orthogonal viewing telescopes that can measure CO2 (daytime absorption) and O2 (day and night emission) lines in the Martian atmosphere. The Thermal Limb Sounder (TLS) instrument measures atmospheric temperature profiles and aerosol (H2O ice clouds, dust) profiles, and the Surface Radiometric Sensor Package (SuRSeP) measures the total reflected solar radiance, and surface temperatures down to 140K. These combined spectral and thermal measurements will provide a new understanding of the global energy balance, dust transport processes, and climate cycles in the Martian atmosphere. The mission concept for Aeolus consists of a single sub-100 kg secondary spacecraft in a highly inclined orbit, allowing it to pass over all local times. Aeolus attains global coverage of the surface for a mission duration of one Martian year, to capture climate patterns during each Martian season. This paper gives an overview of the Aeolus payload, spacecraft, and the methodology used to mature the Aeolus mission concept.

Mauro, David↗

NASA NTRS1992

The Mars Observer laser altimeter investigation

The primary objective of the Mars Observer laser altimeter (MOLA) investigation is to determine globally the topography of Mars at a level suitable for addressing problems in geology and geophysics. Secondary objectives are to characterize the 1064-nm wavelength surface reflectivity of Mars to contribute to analyses of global surface mineralogy and seasonal albedo changes, to assist in addressing problems in atmospheric circulation, and to provide geodetic control and topographic context for the assessment of possible future Mars landing sites. The principal components of MOLA are a diode-pumped, neodymium-doped yttrium aluminum garnet laser transmitter that emits 1064-nm wavelength laser pulses, a 0.5-m-diameter telescope, a silicon avalanche photodiode detector, and a time interval unit with 10-ns resolution. MOLA will provide measurements of the topography of Mars within approximately 160-m footprints and a center-to-center along-track foot print spacing of 300 m along the Mars Observer subspacecraft ground track. The elevation measurements will be quantized with 1.5 m vertical resolution before correction for orbit- and pointing induced errors. MOLA profiles will be assembled into a global 0.2 deg x 0.2 deg grid that will be referenced to Mars' center of mass with an absolute accuracy of approximately 30 m. Other data products will include a global grid of topographic gradients, corrected individual profiles, and a global 0.2 deg x 0.2 deg grid of 1064-nm surface reflectivity.

Zuber, M. T.↗