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NASA NTRS1979

A low-energy gamma-ray imaging detector

We describe a hard-X-ray/soft-gamma-ray imaging detector, incorporating a microchannel-plate (MCP) electron multiplier for possible use in future telescopes. In contrast to previous attempts using MCP's this approach promises to achieve high quantum detection efficiencies in addition to high spatial and temporal resolution. Preliminary results indicate not only the capability of simultaneous imaging and single-photon counting, but also coarse energy resolution.

Yin, L. I.↗

NASA NTRS1983

Periodic substorm activity in the geomagnetic tail

On 19 May 1978 an anusual series of events is observed with the Quadrispherical LEPEDEA on board the ISEE-1 satellite in the Earth's geomagnetic tail. For 13 hours periodic bursts of both ions and electrons are seen in all the particle detectors on the spacecraft. On this day periodic activity is also seen on the ground, where multiple intensifications of the electrojets are observed. At the same time the latitudinal component of the interplanetary magnetic field shows a number of strong southward deflections. It is concluded that an extended period of substorm activity is occurring, which causes repeated thinnings and recoveries of the plasma sheet. These are detected by ISEE, which is situated in the plasma sheet boundary layer, as periodic dropouts and reappearances of the plasma. Comparisons of the observations at ISEE with those at IMP-8, which for a time is engulfed by the plasma sheet, indicate that the activity is relatively localized in spatial extent. For this series of events it is clear that a global approach to magnetospheric dynamics, e.g., reconnection, is inappropriate.

Huang, C. Y.↗

NASA NTRS1983

A method to detect ultra high energy electrons using earth's magnetic field as a radiator

It is pointed out that the detection of electrons with energies exceeding a few TeV, which lose energy rapidly through synchrotron and inverse Compton processes, would provide valuable information on the distribution of sources and on the propagation of cosmic rays in the solar neighborhood. However, it would not be possible to measure the energy spectrum beyond a few TeV with any of the existing experimental techniques. The present investigation is, therefore concerned with the possibility of detecting electrons with energies exceeding a few TeV on the basis of the photons emitted through synchrotron radiation in the earth's magnetic field. Attention is given to the synchrotron radiation of electrons in the earth's magnetic field, detector response and energy estimation, and the characteristics of an ideal detector, capable of detecting photons with energies equal to or greater than 20 keV.

Stephens, S. A.↗

NASA NTRS1988

Laboratory studies of sticking coefficients and heterogeneous reactions important in the Antarctic stratosphere

Laboratory studies of sticking coefficients of H2O, HCl, Cl2, and HNO3 on ice and heterogeneous reactions of ClONO2 with ice or HCl/ice have been performed in a fast flow reactor. A quadrupole mass spectrometer with electron impact ionization was used as a detector. Measured sticking coefficients are: 0.3 (+0.7, -0.1) for H2O, 0.4 (+0.6, -0.2) for HCL, less than 0.0001 for Cl2, and 0.3 (+0.7, -0.1) for HNO3 at 200 K. The reaction probability of ClONO2 on ice was found to be 0.06 (+ or - 0.03) while HOCl was observed as a sole product in the gas phase. With HCl present in ice, the reaction probability of ClONO2 is greatly enhanced, approaching 0.27 (+0.73, -0.13) while molecular chlorine was found to be the major product in the gas phase. Another reaction product was nitric acid which remained in the solid phase. Since the polar stratospheric clouds contain ice particles or possibly HCl/ice particles on the surface, the present results should be a major factor in producing the observed springtime ozone depletion in the Antarctic stratosphere.

Leu, Ming-Taun↗

NASA NTRS1989

Common source cascode amplifiers for integrating IR-FPA applications

Space based astronomical infrared measurements present stringent performance requirements on the infrared detector arrays and their associated readout circuitry. To evaluate the usefulness of commercial CMOS technology for astronomical readout applications a theoretical and experimental evaluation was performed on source follower and common-source cascode integrating amplifiers. Theoretical analysis indicates that for conditions where the input amplifier integration capacitance is limited by the detectors capacitance the input referred rms noise electrons of each amplifier should be equivalent. For conditions of input gate limited capacitance the source follower should provide lower noise. Measurements of test circuits containing both source follower and common source cascode circuits showed substantially lower input referred noise for the common-source cascode input circuits. Noise measurements yielded 4.8 input referred rms noise electrons for an 8.5 minute integration. The signal and noise gain of the common-source cascode amplifier appears to offer substantial advantages in acheiving predicted noise levels.

Woolaway, James T.↗

NASA NTRS1989

Hot plasma and energetic particles in Neptune's magnetosphere

Voyager 2's low energy charged particle instrument employed an array of solid-state detectors in various configurations to measure energetic electrons and ions within the Neptune magnetosphere in several energy channels. Various features of the intensity, spectral, and anisotropic data obtained suggest that the Triton satellite exerts an important controlling influence over the outer regions of the Neptunian magnetosphere. Composition measurements have indicated the presence of H, H2, and He-4 at 1300:1:0.1 relative abundances, respectively, suggesting a Neptunian ionospheric source for the trapped particle population.

Krimigis, S. M.↗

NASA NTRS1989

Search for soft X-ray emission from SN 1987A with a CCD X-ray imaging spectrometer

The results of soft X-ray observations of SN 1987A over the energy band 0.65-2.0 keV are reported. The upper limits on the soft X-ray flux are inconsistent with an extrapolation of the spectrum measured by the Ginga Satellite to the energy band and require a turnover in the X-ray spectrum between 2 and 4 keV. If this turnover is due to absorption by intervening material, a neutral column density associated with the supernova of at least 2.8 x 10 to the 21st/sq cm is required. The background rate for the Texas Instruments 800 x 800 pixel CCD, measured between 150 and 285 km altitude, was 1.1 counts/sq cm s. The background spectrum has a broad peak at 350 electrons, corresponding to charge deposited in the detector by minimally ionizing particles.

Burrows, D. N.↗

NASA NTRS1990

Thermal Infrared Imaging Spectrometer - An advanced optics technology instrument

Through the use of a special optical filter, the Thermal Infrared Imaging Spectrometer, an airborne multispectral IR imaging instrument operating in the thermal emission region (7.5-14 microns), will achieve signal-to-noise ratios greater than 600 with ambient temperature optics. This instrument will be used to do compositional surface mapping of the terrain, and will refine the ability to categorize rock families and types by providing much higher spectral resolution in the emission region than was previously available. Details of the optical system, the detector, the cooler system, and the support electronics are described.

Mahoney, Colin↗

NASA NTRS1992

Gas ionization solar spectral monitor (GISSMO)

We are currently developing an instrument free from optical components to measure the full-disk solar spectrum in the extreme ultraviolet regime covering wavelengths from 75-500 A. The instrument, which will be launched aboard a NASA Black Brant sounding rocket in September 1992, consists of a windowless noble gas ionization cell followed by a toroidal electrostatic analyzer to spatially disperse photoelectrons as a function of their energies. A microchannel plate based position sensitive detector will be used to detect individual electrons, indirectly returning the solar EUV spectrum.

Vickers, James S.↗

NASA NTRS1993

X ray, extreme and far ultraviolet optical thin films for space applications

Far and extreme ultraviolet optical thin film filters find many uses in space astronomy, space astrophysics, and space aeronomy. Spacebased spectrographs are used for studying emission and absorption features of the earth, planets, sun, stars, and the interstellar medium. Most of these spectrographs use transmission or reflection filters. This requirement has prompted a search for selective filtering coatings with high throughput in the FUV and EUV spectral region. Important progress toward the development of thin film filters with improved efficiency and stability has been made in recent years. The goal for this field is the minimization of absorption to get high throughput and enhancement of wavelength selection. The Optical Aeronomy Laboratory (OAL) at the University of Alabama in Huntsville has recently developed the technology to determine optical constants of bulk and film materials for wavelengths extending from x-rays (0.1 nm) to the FUV (200 nm), and several materials have been identified that were used for designs of various optical devices which previously have been restricted to space application in the visible and near infrared. A new design concept called the Pi-multilayer was introduced and applied to the design of optical coatings for wavelengths extending from x-rays to the FUV. Section 3 of this report explains the Pi-multilayer approach and demonstrates its application for the design and fabrication of the FUV coatings. Two layer Pi-stacks have been utilized for the design of reflection filters in the EUV wavelength range from 70 - 100 nm. In order to eliminate losses due to the low reflection of the imaging optics and increase throughput and out-of-band rejection of the EUV instrumentation we introduced a self-filtering camera concept. In the FUV region, MgF2 and LiF crystals are known to be birefringent. Transmission polarizers and quarterwave retarders made of MgF2 or LiF crystals are commercially available but the performances are poor. New techniques for the design of the EUV and FUV polarizers and quarterwave retarders are described in Section 5. X- and gamma-ray detectors rely on a measurement of the electron which is effected when a ray interacts with matter. The design of an x- and gamma-ray telescope to operate in a particular region of the spectrum is, therefore, largely dictated by the mechanism through which the rays interact. Energy selection and the focusing of the incident high energy rays can be achieved with spectrally selective high reflective multilayers. The design and spectral performance of narrowband reflective x-ray Pi-multilayers are presented in section 6.

Zukic, Muamer↗

NASA NTRS1994

Investigation of the effects of long duration space exposure on active optical system components

This experiment was exposed to the space environment for 6 years on the Long Duration Exposure Facility (LDEF). It investigated quantitatively the effects of the long-duration space exposure on the relevant performance parameters of a representative set of electron-optic system components, including lasers, radiation detectors, filters, modulators, windows, and other related components. It evaluated the results and implications of the measurements indicating real or suspected degradation mechanisms. This information will be used to establish guidelines for the selection and use of components for space-based, electro-optic systems.

Blue, M. D.↗

NASA NTRS1993

High T(sub c) leads for remote sensing applications

Several NASA programs designed to monitor the Earth's atmosphere from space utilize infrared detectors which operate at or below 4.2 K for optimum performance. At present, the detectors are maintained at cryogenic temperatures by a stored volume of liquid helium. These detectors must be electrically linked to amplification electronics data storage instruments maintained at 80 K. The electrical connections over the temperature gradient account for approximately 20% of the total heat load on the Dewar for some systems, accelerating the boil-off of liquid helium cryogen and reducing the operational lifetime of the space-borne instruments. The recent discovery of high temperature superconductors has provided an opportunity to develop electrically conductive, thermally insulating links to bridge this thermal gradient. This paper describes the modelling of the thermal transport properties of thick film, high T(sub c) electrical bridges across a 4.2-80 K temperature gradient and the impact of such devices on a spaceborne remote sensing system.

Selim, R.↗

NASA NTRS1995

Centroid Detector Assembly for the AXAF-I Alignment Test System

The High Resolution Mirror Assembly (HRMA) of the Advanced X-ray Astrophysics Facility (imaging) (AXAF-I) consists of four nested paraboloids and four nested hyperboloids, all of meter-class size, and all of which are to be assembled and aligned in a special 15 meter tower at Eastman Kodak Company in Rochester, NY. The goals of the alignment are (1) to make the images of the four telescopes coincident; (2) to remove coma from each image individually; and (3) to control and determine the final position of the composite focus. This will be accomplished by the HRMA Aligment Test System (HATS) which is essentially a scanning Hartmann test system. The scanning laser source and the focal plane of the HATS are part of the Centroid Detector Assembly (CDA) which also includes processing electronics and software. In this paper we discuss the design and the measured performance of the CDA.

Glenn, Paul↗

NASA NTRS2004

An Overview of Lunar Calibration and Characterization for the EOS Terra and Aqua MODIS

The Moon can be used as a stable source for Earth-observing sensors on-orbit radiometric and spatial stability monitoring in the VIS and NIR spectral regions. It can also serve as a calibration transfer vehicle among multiple sensors. Nearly identical copies of the Moderate Resolution Imaging Spectroradiometer (MODE) have been operating on-board the NASA's Earth Observing System (EOS) Terra and Aqua satellites since their launches in December 1999 and May 2002, respectively. Terra and Aqua MODIS each make observations in 36 spectral bands covering the spectral range from 0.41 to 14.5 microns and are calibrated on-orbit by a set of on-board calibrations (OBCs) including: 1) a solar diffuser (SD), 2) a solar diffuser stability monitor (SDSM), 3) a blackbody (BB), and 4) a spectro-radiometric calibration assembly (SRCA). In addition to fully utilizing the OBCs, the Moon has been used extensively by both Terra and Aqua MODIS to support their on-orbit calibration and characterization. A 4 This paper provides an overview of applications of lunar calibration and characterization from the MODIS perspective, including monitoring radiometric calibration stability for the reflective solar bands (RSBs), tracking changes of the sensors response versus scan-angle (RVS), examining the sensors spatial performance , and characterizing optical leaks and electronic crosstalk among different spectral bands and detectors. On-orbit calibration consistency between the two MODIS instruments is also addressed. Based on the existing on-orbit time series of the Terra and Aqua MODIS lunar observations, the radiometric difference between the two sensors is less than +/-1% for the RSBs. This method provides a powerful means of performing calibration comparisons among Earth-observing sensors and assures consistent data and science products for the long-term studies of climate and environmental changes.

Xiong, X.↗

NASA NTRS1999

Crystal Growth Using MEPHISTO

The shuttle flight experiment "In Situ Monitoring of Crystal Growth Using MEPHISTO" was accomplished during STS-87 as part of the fourth flight of the United States Microgravity Payload (USMP-4), which was flown from November 19 to December 5, 1997. The data returned from that flight are just now beginning to yield quantitative results. This project is an international collaboration: the furnace system known as MEPHISTO was built in France by CNES (French National Space Agency) and CEA (French Atomic Energy Commission); the principal investigator, Prof. Reza Abbaschian, is from the University of Florida at Gainesville; and numerical and analytical modeling support includes collaborators from the University of New South Wales, Australia, the University of Wisconsin at Milwaukee, the National Institute of Standards and Technology, and the NASA Lewis Research Center. MEPHISTO is a French acronym that translates into English as Materials for the Study of Interesting Phenomena of Solidification on Earth and in Orbit. Since this was the fourth flight of the MEPHISTO furnace, the experiment is referred to as MEPHISTO-4. MEPHISTO-4 was a directional solidification experiment that studied the liquid-to-solid transformation of bismuth alloyed with tin. Directional solidification is a freezing technique common to the processing of the electronic materials used in integrated circuits and detectors, such as silicon and germanium. When liquids are frozen on Earth, they must be cooled. The cooling causes stirring because of density variations in the liquid. This stirring, known as natural convection, influences the quality of the resulting solid. During freezing, regions of high and low concentrations of tin are created. This introduces another important phenomenon: diffusion, or the movement by molecular action of matter from regions of high concentration to regions of lower concentration. In MEPHISTO-4, it is tin that diffuses from the high-concentration region in front of the solid-liquid interface to more distant low-concentration regions.

deGroh, Henry C., III↗

NASA NTRS1993

Micromachined Tunneling Displacement Transducers for Physical Sensors

We have designed and constructed a series of tunneling sensors which take advantage of the extreme position sensitivity of electron tunneling. In these sensors, a tunneling displacement transducer, based on scanning tunneling microscopy principles, is used to detect the signal-induced motion of a sensor element. Through the use of high-resonant frequency mechanical elements for the transducer, sensors may be constructed which offer wide bandwidth, and are robust and easily operated. Silicon micromachining may be used to fabricate the transducer elements, allowing integration of sensor and control electronics. Examples of tunneling accelerometers and infrared detectors will be discussed. In each case, the use of the tunneling transducer allows miniaturization of the sensor as well as enhancement of the sensor performance.

Kenny, T. W.↗

NASA NTRS2012

New Techniques for High-Contrast Imaging with ADI: The ACORNS-ADI SEEDS Data Reduction Pipeline

We describe Algorithms for Calibration, Optimized Registration, and Nulling the Star in Angular Differential Imaging (ACORNS-ADI), a new, parallelized software package to reduce high-contrast imaging data, and its application to data from the Strategic Exploration of Exoplanets and Disks (SEEDS) survey. We implement seyeral new algorithms, includbg a method to centroid saturated images, a trimmed mean for combining an image sequence that reduces noise by up to approx 20%, and a robust and computationally fast method to compute the sensitivitv of a high-contrast obsen-ation everywhere on the field-of-view without introducing artificial sources. We also include a description of image processing steps to remove electronic artifacts specific to Hawaii2-RG detectors like the one used for SEEDS, and a detailed analysis of the Locally Optimized Combination of Images (LOCI) algorithm commonly used to reduce high-contrast imaging data. ACORNS-ADI is efficient and open-source, and includes several optional features which may improve performance on data from other instruments. ACORNS-ADI is freely available for download at www.github.com/t-brandt/acorns_-adi under a BSD license

Brandt, Timothy D.↗

NASA NTRS2015

Maturing CCD Photon-Counting Technology for Space Flight

This paper discusses charge blooming and starlight saturation - two potential technical problems - when using an Electron Multiplying Charge Coupled Device (EMCCD) type detector in a high-contrast instrument for imaging exoplanets. These problems especially affect an interferometric type coronagraph - coronagraphs that do not use a mask to physically block starlight in the science channel of the instrument. These problems are presented using images taken with a commercial Princeton Instrument EMCCD camera in the Goddard Space Flight Center's (GSFC), Interferometric Coronagraph facility. In addition, this paper discusses techniques to overcome such problems. This paper also discusses the development and architecture of a Field Programmable Gate Array and Digital-to-Analog Converter based shaped clock controller for a photon-counting EMCCD camera. The discussion contained here will inform high-contrast imaging groups in their work with EMCCD detectors.

Mallik, Udayan↗