Engineering topics

Timothy, J. G.

Publications and source records attributed to Timothy, J. G..

At least 19 records

NASA NTRS1994

Speckle imaging with the MAMA detector: Preliminary results

We report on the first successful speckle imaging studies using the Stanford University speckle interferometry system, an instrument that uses a multianode microchannel array (MAMA) detector as the imaging device. The method of producing high-resolution images is based on the analysis of so-called 'near-axis' bispectral subplanes and follows the work of Lohmann et al. (1983). In order to improve the signal-to-noise ratio in the bispectrum, the frame-oversampling technique of Nakajima et al. (1989) is also employed. We present speckle imaging results of binary stars and other objects from V magnitude 5.5 to 11, and the quality of these images is studied. While the Stanford system is capable of good speckle imaging results, it is limited by the overall quantum efficiency of the current MAMA detector (which is due to the response of the photocathode at visible wavelengths and other detector properties) and by channel saturation of the microchannel plate. Both affect the signal-to-noise ratio of the power spectrum and bispectrum.

Horch, E.↗

NASA NTRS1993

Microchannel plate modal gain variations with temperature

Measurements of the modal gain of two high-gain curved-channel microchannel plates (MCPs) at various operating temperatures are presented. Both MCPs were fabricated from the Long Life glass with 12-micron diam channels on 15-micron centers. The modal gain was found to decrease with increasing temperature at a rate of -0.1 percent C. This reduction of gain with temperature is attributed primarily to an axial temperature gradient along each MCP channel creating a nonuniform electric field within the channel that lowers the effective output gain. A lowering of the secondary electron yield resulting from increased phonon scattering of secondary electrons released within the walls of the MCP channels was assessed, but was found to have a negligible contribution to the drop in gain with temperature.

Slater, David C.↗

NASA NTRS1993

Preliminary results from the MAMA detectors for the SOHO mission

Multi-Anode Microchannel Array (MAMA) detector systems are being fabricated and tested for use in the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) and the Ultraviolet Coronagraph Spectrometer (UVCS) instruments on the ESA/NASA Solar and Heliospheric Observatory (SOHO) mission. The SOHO MAMA detector systems have formats of 360 x 1024 pixels and pixel dimensions of 25 x 25 sq microns and are optimized for operation at Extreme Ultraviolet (EUV) wavelengths between 40 and 160 nm. In this paper we report on the initial results of measurements of the performance characteristics of the first flight-configuration detector system employing the new custom Application Specific Integrated Circuits (ASICs) which are designed to improve both the dynamic range and the uniformity of response. The performance characteristics of this detector system are compared with those of earlier breadboard systems employing discrete-component electronics circuits.

Slater, David C.↗

NASA NTRS1993

HiRES - High Resolution Extreme Ultraviolet Spectroheliometer toroidal diffraction grating performance evaluation

The ray-tracing results presented characterize the theoretically achievable EUV performance of the HiRES instrument. The effects of optical system misalignment on spectrograph images, and the laboratory results for two f/15 toroidal diffraction gratings that employ a multianode microchannel array, are also presented. Interferometric studies of toroidal figure accuracy, as well as optical and electron microscopy investigations of surface quality, are discussed. While the current toroidal gratings are noted to furnish good imaging across a wide wavelength range, they exhibit excessive EUV scatter, as well as spectral ghosting.

Berger, Thomas E.↗

NASA NTRS1993

Ultra high resolution images of the solar chromosphere and corona using coordinated rocket and balloon observations

A discussion is presented of the scientific objectives that can be pursued by simultaneous coronal/chromospheric observation with the Multi-Spectral Solar Telescope Array (MSSTA), and a new balloon-borne observatory called the Ultra-High Resolution Vacuum Ultraviolet Spectroheliograph (UHRVS). Attention is given to the proposed UHRVS observatory, which will incorporate two instruments, a 65-cm aperture telescope with narrowband filters for high resolution photographic and photoelectric spectroheliograms, and a very high resolution spectrograph which uses a 40-cm aperture telescope. The capabilities of the MSSTA, and the joint UHRVS/MSSTA observing program that is envisioned are reviewed.

Walker, Arthur B. C., Jr.↗

NASA NTRS1992

Far-ultraviolet MAMA detector imagery and emission-line CCD imagery of NGC 6240

An image of the luminous infrared galaxy NGC 6240 at 1480 A was obtained using a multianode microchannel array (MAMA) detector with a rocket-borne telescope. At distances greater than 12 arcsec from the nucleus, the measured ultraviolet luminosity implies intensive star formation activity equal to 2-3 times that of a spiral galaxy such as M83. Optical images in the H-beta and forbidden O III 5007 A emission lines reveal a region of high excitation east of the nucleus between the centers of disks 1 and 2 as described by Bland-Hawthorn et al.

Smith, Andrew M.↗

NASA NTRS1992

The Ultra High Resolution XUV Spectroheliograph. III - A modified configuration for a free flying platform

The Ultra-High Resolution XUV Spectroheliograph (UHRXS) is a comprehensive solar observatory capable of studying solar phenomena at soft X-ray, XUV, EUV, and VUV wavelengths with normal incidence imaging multilayer telescopes capable of very high angular resolution (about 0.1 arcsec), and spectrographs able to achieve high spectral resolution. This instrument has been selected by NASA for flight as an attached payload on the Space Station Freedom. Recent developments have made it clear that accommodations for attached payloads on Freedom will not become available during the initial operations of Freedom and may never be available. We have studied the changes that must be made to place the UHRXS instrument on a Free Flying Plafform such as the Delta Launched Explorer Bus. We report on the configuration, performance, and accommodation on a free flying platform of the revised UHRXS concept.

Walker, Arthur B. C., Jr.↗

NASA NTRS1992

The Solar/Stellar Coronal Explorer and the Solar/Stellar Coronal Observatory

The Solar/Stellar Coronal Explorer (SSCE) carries six identical Ritchey-Chretien Telescopes of 127 mm aperture each; their images will be recorded by multianode microchannel-array detectors. The mirrors of five of the telescopes are coated with multilayer reflecting structures that select narrow XUV wavelength bands corresponding to strong emission lines emitted by solar or stellar coronal plasmas. Also noted here is a larger explorer mission concept, that of the Solar/Stellar Coronal Observatory, which will undertake more extensive spectroscopic observations.

Walker, Arthur B. C., Jr.↗

NASA NTRS1992

Design and test of a High-Resolution EUV Spectroheliometer

The HiRES High-Resolution EUV Spectroheliometer is a sounding rocket instrument yielding very high spatial, spectral, and temporal resolution images of the solar outer atmosphere, on the basis of a 45-cm Gregorian telescope feeding a normal-incidence stigmatic EUV spectrometer with imaging multianode microchannel-array detector system, as well as an IR spectrometer with imaging CCD detector system. Attention is given to the expected performance of this system, including the effects of vibrational misalignments due to the sounding rocket flight environment.

Berger, Thomas E.↗

NASA NTRS1991

The Ultra High Resolution XUV Spectroheliograph. II - Predicted performance

The phenomena to be studied with the Ultra-High Resolution XUV Spectroheliograph (UHRXS) which will be included into the instrumental load of the Space Station Freedom are discussed together with the characteristics of the nine multilayer Ritchey-Chretien telescopes constituting the UHRXS system. The telescopes will cover a spectral range from about 70 A to about 300 A. Each telescope will be able to isolate emission line multiplets excited over a narrow temperature range, providing images of diagnostic quality covering structures in the solar atmosphere ranging from T of about 50,000 K to 30,000,000 K. One of the nine UHRXS telescopes is configured as a coronagraph to allow observations to 6 solar radii beyond the solar limb. The paper presents an analysis of the expected sensitivity and resolving power of the UHRXS telescopes, and the diagnostic response of the various UHRXS instruments to structures in the solar atmosphere between 10,000 K and 100,000,000 K.

Walker, Arthur B. C., Jr.↗

NASA NTRS1991

The Active Sun Telescope Array

The concept of the Active Sun Telescope Array (ASTA) designed as a part of the NASA Orbiting Solar Laboratory is described together with the details of the ASTA instrument package. The ASTA, which will investigate the phenomenology of the solar chromosphere and the corona, consists of six EUV/XUV solar telescopes designed to provide wide field solar images in narrow wavelength bands, high-resolution spectroheliograms, and line profiles of the solar plasma in the temperature range from 10,000 K to 30,000 K. The detectors used in the ASTA are of the multianode multichannel array photon-counting array detector type.

Walker, Arthur B. C., Jr.↗

NASA NTRS1991

High resolution imaging with multilayer soft X-ray, EUV and FUV telescopes of modest aperture and cost

The development of multilayer reflective coatings now permits soft X-ray, EUV and FUV radiation to be efficiently imaged by conventional normal incidence optical configurations. Telescopes with quite modest apertures can, in principle, achieve images with resolutions which would require apertures of 1.25 meters or more at visible wavelengths. The progress is reviewed which has been made in developing compact telescopes for ultra-high resolution imaging of the sun at soft X-ray, EUV and FUV wavelengths, including laboratory test results and astronomical images obtained with rocket-borne multilayer telescopes. The factors are discussed which limit the resolution which has been achieved so far, and the problems which must be addressed to attain, and surpass the 0.1 arc-second level. The application of these technologies to the development of solar telescopes for future space missions is also described.

Walker, Arthur B. C., Jr.↗

NASA NTRS1991

Imaging pulse-counting detector systems for space ultraviolet astrophysics missions

A family of imaging, pulse-counting, photoelectric detector systems, the Multi-Anode Microchannel Arrays (MAMAs), are now under active development for use on a number of space ultraviolet astrophysics missions at far-ultraviolet (FUV) and extreme-ultraviolet wavelengths between about 300 and 28 nm. Specifically, MAMA detectors are being fabricated and tested for use in two instruments on the ESA/NASA Solar and Heliospheric Observatory mission, for the NASA Goddard Space Flight Center's Hubble Space Telescope Imaging Spectrograph, and for the prime FUV spectrograph of the Far Ultraviolet Spectroscopic Explorer FUSE/Lyman mission. The construction and performance characteristics of the different MAMA detector systems are described, and techniques for improving the spatial resolution of each of the detector systems by the use of custom application specific integrated circuits in the electronics are discussed.

Timothy, J. G.↗

NASA NTRS1991

The fabrication of toroidal and coma-corrected toroidal diffraction gratings from spherical master gratings using elastically-deformable substrates - A progress report

A technique has been developed which permits toroidal, and coma-corrected toroidal, diffraction gratings to be replicated from spherical master gratings by the use of elastically-deformable substrates. Toroidal gratings correct for astigmatism and, thus, make it possible to construct stigmatic spectrometers that employ a single reflective diffraction grating. These spectrometers are particularly useful for the extreme-ultraviolet (EUV) wavelength range, where reflection coefficients are low, since the single optical surface provides for dispersion, focusing, and astigmatism correction. The fabrication procedures for the pure toroidal, and coma-corrected toroidal, gratings are described, and initial test results are presented. The use of the toroidal gratings in a high-resolution sounding-rocket EUV spectroheliometer, and in both the coronal diagnostics spectrometer and the ultraviolet coronagraph spectrometer on the ESA/NASA solar and heliospheric observatory mission, is described briefly, and the use of this technique for the fabrication of a coma-corrected toroidal grating for the prime Rowland spectrograph of the FUSE/Lyman mission is briefly discussed.

Huber, Martin C. E.↗

NASA NTRS1991

High-dynamic-range MCP structures

We report on the development of a new high-dynamic-range two-stage Multi-Anode Microchannel Array (MAMA) imaging tube designed for improved high count rate performance at FUV and EUV wavelengths. The new two-stage MAMA tube employs two 25-mm-diameter format MCPs placed in tandem with a small gap between the plates. The front (input) MCP is designed to be a low-gain converter plate that supports an opaque photocathode and converts the detected photons to electrons, while the second (output) MCP is of higher conductivity and thus maintains the overall gain of the multiplier at high count rates. The second MCP is mounted in proximity focus with a (224 x 960)-pixel fine-fine coincidence MAMA array for high-spatial-resolution imaging studies. The applied voltage across each MCP can be controlled independently. We report on the gain and dynamic range performance characteristics of the two-stage MAMA tube in two different configurations: first, with the output MCP having moderate conductivity (about 100 MOhm); and second, with the output MCP having very high conductivity (about 2 MOhm). These results are compared and contrasted with those of the more conventional MAMA tube configuration which employs a single high-gain curved-channel MCP.

Slater, David C.↗

NASA NTRS1991

Performance characteristics of the imaging MAMA detector systems for SOHO, STIS, and FUSE/Lyman

Imaging Extreme Ultraviolet (EUV) Multi-Anode Microchannel Array (MAMA) detector systems with formats of 360 x 1024 pixels and pixel dimensions of 25 x 25 sq microns are being fabricated and tested for flight in two instruments on the ESA/NASA Solar and Heliospheric Observatory (SOHO). In addition, very-large-format (1024 x 1024)- and (2048 x 2048)-pixel Far Ultraviolet (FUV) and EUV MAMA detectors with pixel dimensions of 25 x 25 sq microns are being fabricated and tested for use in the NASA Goddard Space Flight Center's Hubble Space Telescope Imaging Spectrograph (STIS), a second-generation instrument scheduled for in-orbit installation in 1997. Finally, FUV MAMA detectors with formats of 224 x 960 pixels and pixel dimensions of 14 x 14 sq microns are being evaluated as prototypes of the detector for the prime FUV spectrograph of the Far Ultraviolet Spectroscopic Explorer (FUSE/Lyman) mission. The configurations and performance characteristics of the different detector systems are described, and the plans for further development of the Advanced Technology MAMA detector system discussed.

Timothy, J. G.↗

NASA NTRS1990

Imaging MAMA detector systems

Imaging multianode microchannel array (MAMA) detector systems with 1024 x 1024 pixel formats have been produced for visible and UV wavelengths; the UV types employ 'solar blind' photocathodes whose detective quantum efficiencies are significantly higher than those of currently available CCDs operating at far-UV and EUV wavelengths. Attention is presently given to the configurations and performance capabilities of state-of-the-art MAMA detectors, with a view to the development requirements of the hybrid electronic circuits needed for forthcoming spacecraft-sensor applications. Gain, dark noise, uniformity, and dynamic range performance data are presented for the curved-channel 'chevron', 'Z-plate', and helical-channel high gain microchannel plate configurations that are currently under evaluation with MAMA detector systems.

Slater, David C.↗

NASA NTRS1990

Astronomical EUV/X-ray observatories on the moon

A proposed Lunar EUV/X-ray/Far-Ultraviolet Observatory (LEXO) is described, which consists of a monolithic array of multilayer, grazing incidence, and far-UV telescopes, coronagraphs, and spectroscopic instruments for ultrahigh spectral and spatial resolution investigations of the sun from the lunar base. The LEXO can provide a very powerful observational tool for the study of numerous critical issues in galactic and extragalactic astronomy. The advantages of performing both solar and nonsolar observations with a single LEXO are discussed.

Walker, Arthur B. C., Jr.↗