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NASA NTRS2007

Characterization of MODIS Solar Diffuser On-orbit Degradation

MODIS reflective solar bands (RSB) are calibrated on-orbit by a solar diffuser (SD) and a solar diffuser stability monitor (SDSM). The SD bi-directional reflectance factor (BRF) was characterized pre-launch by the instrument vendor using reference samples traceable to NIST reflectance standards. Its on-orbit degradation is regularly monitored by the SDSM. It consists of a solar integration sphere (SIS) with 9 filtered detectors with wavelengths ranging from 0.41 to 0.94 micrometer, a rotating mirror assembly, and an electronics module. During each SD/SDSM calibration, the SDSM views the sunlight directly and the sunlight diffusely reflected from the SD panel. The time series of SDSM measurements (ratio of the SD view response to the Sun view response) is used to compute the SD BRF degradation at each SDSM detector wavelength. Since launch Terra MODIS has operated for more than seven years and Aqua for nearly five years. The SD panel on each MODIS instrument has experienced noticeable degradation with the largest changes observed in the VIS spectral region. Following a brief description of the MODIS RSB calibration methodology and SD/SDSM operational activities, this paper illustrates the SD on-orbit degradation results for both Terra and Aqua MODIS. It discusses the impacts on the SD RF degradation due to sensor operational conditions and SD solar exposure time. For Aqua MODIS, operated under the same conditions, the SD annual degradation rate is approximately 2.9% at 0.41 micrometers, 1.6% at 0.47 micrometers, and less than 1.1% at wavelengths above 0.53 micrometers. For Terra MODIS, however, an SD door (SDD) related anomaly in May 2003 had led to a decision to keep the SDD permanently at its open position. Since then its SD has experienced a much faster SD degradation rate.

Xiong, X.↗
NASA NTRS2017

Investigation of Deuterium Loaded Materials Subject to X-Ray Exposure

Results are presented from an exploratory study involving x-ray irradiation of select deuterated materials. Titanium deuteride plus deuterated polyethylene, deuterated polyethylene alone, and for control, hydrogen-based polyethylene samples and nondeuterated titanium samples were exposed to x-ray irradiation. These samples were exposed to various energy levels from 65 to 280 kV with prescribed electron flux from 500 to 9000 μA impinging on a tungsten braking target, with total exposure times ranging from 55 to 280 min. Gamma activity was measured using a high-purity germanium (HPGe) detector, and for all samples no gamma activity above background was detected. Alpha and beta activities were measured using a gas proportional counter, and for select samples beta activity was measured with a liquid scintillator spectrometer. The majority of the deuterated materials subjected to the microfocus x-ray irradiation exhibited postexposure beta activity above background and several showed short-lived alpha activity. The HPE and nondeuterated titanium control samples exposed to the x-ray irradiation showed no postexposure alpha or beta activities above background. Several of the samples (SL10A, SL16, SL17A) showed beta activity above background with a greater than 4σ confidence level, months after exposure. Portions of SL10A, SL16, and SL17A samples were also scanned using a beta scintillator and found to have beta activity in the tritium energy band, continuing without noticeable decay for over 12 months. Beta scintillation investigation of as-received materials (before x-ray exposure) showed no beta activity in the tritium energy band, indicating the beta emitters were not in the starting materials.

x-ray irradiation↗
NASA NTRS2005

Monitoring the Intrinsic Absorption Complex Toward RX J1230.8+115

There is a very prominent intrinsic absorption complex in the spectrum of the quasar RX J1230.8+115. It was diagnosed as intrinsic due to partial covering of the quasar by the absorber, which can only happen for material very near to the quasar. Measuring a variability timescale for the absorption would allow us to place a more stringent constraint on the distance of the absorber from the central engine. Furthermore, understanding the variability and covering factors in different transitions can help to identify if it is due to changes in the ionizing source or transverse motion of the absorber. The OVI doublet is covered in the FUSE wavelength range. Unfortunately, our initial target, RX J1230.8+0115 could not be observed due to the failure of the first reaction wheel. We determined that another target, H 1821+643, could be observed and would satisfy similar science goals, understanding intrinsic narrow absorption line systems. Our specific goal for that target was to search for Ne VI11 absorption from the associated absorber. This observation was attempted, but the counts in the Sic channel, where the absorption was expected to lie, were too low to satisfy our science goal. This was, at least in part, due to a misalignment of the SiC mirrors. Because of this problem, more time was awarded. However, even the extra time was too little. It appears that the quasar may be too faint to properly align all the mirrors. So with disappointment, I report that we were not able to accomplish our science goals for this program. The funds were used to support my work with a graduate student, Jie Ding, to evaluate possible replacement targets once we learned that Rx J1230.8+115 would not be observable. We considered the intrinsic NAL candidates that we could find through a partial coverage analysis of doublets in the STIS E140M and E230M quasar spectra taken from the HST archive. We then checked the flux in the FUSE wavelength range, and in most cases of interest it was found to be too low to satisfy our S/N requirement in the exposure time we had been awarded. We decided that H1821+643 was the best choice for this project, even though the associated absorber we would be studying might in fact originate in the cluster with the quasar and not in intrinsic gas. Part of the appeal of the target, was in fact the opportunity to consider this issue. Please do not hesitate to contact me if more detail is needed for this report. I found it difficult to write a satisfying report under the circumstance and am uncertain if I've provided the proper level of information.

Charlton, Jane↗
NASA NTRS1992

Summary of ionizing radiation analysis on the Long Duration Exposure Facility

The ionizing radiation measurements flown on the Long Duration Exposure Facility (LDEF) were contained in 15 experiments which utilized passive detectors to pursue objectives in astrophysics and to measure the radiation environment and dosimetric quantities. The spacecraft structure became sufficiently radioactive to permit additional important studies. The induced activity allows extensive radiation mapping in the structure, and independent comparison with experiment dosimetric techniques, and significant studies of secondary effects. The long exposure time, attitude stability, and number and types of measurements produced a unique and critical set of data for low Earth orbit that will not be duplicated for more than a decade. The data allow an unprecedented test, and improvement if required, of models of the radiation environment and the radiation transport methods that are used to calculate the internal radiation and its effects in spacecraft. Results of measurements in the experiments, as well as from radioactivity in the structure, have clearly shown effects from the directional properties of the radiation environment, and progress was made in the dosimetric mapping of LDEF. These measurements have already influenced some Space Station Freedom design requirements. Preliminary results from experiments, reported at this symposium and in earlier papers, show that the 5.8 years exposure considerably enhanced the scientific return of the radiation measurements. The early results give confidence that the experiments will make significant advances in the knowledge of ultra heavy cosmic rays, anomalous cosmic rays, and heavy ions trapped in the radiation belts. Unexpected phenomena were observed, which require explanation. These include stopping iron group ions between the energy ranges anticipated for anomalous and galactic cosmic rays in the LDEF orbit. A surprising concentration of the Be-7 nuclide was discovered on the 'front' surface of LDEF, apparently transported up from the stratosphere with exceptional efficiency.

Parnell, T. A.↗
NASA NTRS2004

Optical Design of the RAISE Sounding Rocket Instrument

The Rapid Acquisition Imaging Spectrograph Experiment (RAISE) is a recently selected sounding rocket program to investigate the dynamics and heating of the outer solar atmosphere on time scales as short as looms. Its optical design represents the first in a new class of two-reflection W / E W imaging spectrometers with Toroidal Varied-Line Space (TVLS) gratings. Due to the remarkable imaging properties of such gratings, RAISE will measure spectra simultaneously over four different wavelength bands (1205-1243 & 1524-1559 A in first order, 602.5-621.5 & 762.0-779.5 A in second), with an unprecedented combination of spatial, spectral, and temporal resolutions. These spectral regions include many bright, well-resolved lines covering the temperature range from the low chromosphere up to the 2 MK Fe XI1 corona. The RAISE optical design features an extremely fast beam (f/7.0) and a minimum number of reflections, which together allow enough throughput to provide high quality spectral data even at its very short exposure times. Moreover, by operating with high magnification (x4.25), the RAISE spectrometer can most effectively utilize the full length and width available in the sounding rocket payload. First launch of this exciting new instrument is scheduled for 2006 June 21.

Thomas, Roger J.↗
NASA NTRS1990

Signal-to-noise ratios in IUE SWP-LO spectra of chromospheric emission-line sources

The short-wavelength-prime (SWP) detector of the International Ultraviolet Explorer should operate near the photon-counting limit, but the noise levels in flat-field images are several times higher. The exaggerated noise can be traced to the incomplete removal of the pixel-to-pixel granularity of the television frames by the prevailing spectral image processing system. An empirical noise model for the current-epoch photometric linearization strategy and one for a hypothetical processing system that achieves complete flat fielding of the raw images are derived. A formula is then proposed to predict the signal-to-noise ratio in the measured flux of an emission line (possibly superimposed on a smooth continuum) in an IUE low-dispersion (5 A resolution) far-ultraviolet (1150 A-1950 A) spectrum as recorded with the SWP camera. For illustration, the formula is specialized to the important C IV 1549 A feature of F-K stars. The S/N relation permits one to determine sensitivity limits, upper limits in faint exposures, and optimum exposure times.

Ayres, Thomas R.↗
NASA NTRS1995

Room-Temperature Fluorine-Induced Decrease in the Stability of Bromine and Iodine Intercalated Carbon Fibers

Upon exposure to room-temperature fluorine, intercalated carbon fibers (containing either bromine alone or iodine and bromine together) become heavier and less stable. For Amoco P-100 graphitized carbon fibers, which were intercalated with 18 wt percent bromine, 1 hour of fluorine exposure resulted in a large weight increase but caused only a small decrease in thermal stability. An additional 89 hours of fluorine exposure time resulted in small additional increases in fiber weight, but significant further decreases in fiber thermal stability. Such phenomena of weight increase and stability decrease do not occur if the intercalated fibers are exposed to 250 C fluorine. These observations suggest that, at room temperature, fluorine is absorbed quickly by the intercalated fibers and is intercalated slowly into the fibers. Most of the original intercalates are replaced by fluorine in the process of fluorine intercalation. In an inert environment, the bromine intercalated fibers are much more thermally stable. After 800 C vacuum heating for 2 weeks, the brominated fibers lost about 45% of their bromine, and their resistivity increased from 64 mu(Omega)-cm to a range of 95-170 mu(Omega)-cm. This is still much lower than the value of 300 mu(Omega)-cm for pristine P-100. For practical purposes, to preserve their thermal stability, brominated fibers need to be protected from exposure to fluorine at room temperature or to any intercalate at a temperature where, upon direct contact with graphite, an intercalation compound can easily be formed.

Hung, Ching-Cheh↗
NASA NTRS2007

An Attempt to Observe Debris from the Breakup of a Titan 3C-4 Transtage

In February 2007 dedicated observations were made of the orbital space predicted to contain debris from the breakup of the Titan 3C-4 transtage back on February 21, 1992. These observations were carried out on the Michigan Orbital DEbris Survey Telescope (MODEST) in Chile with its 1.3deg field of view. The search region or orbital space (inclination and right ascension of the ascending node (RAAN) was predicted using NASA#s LEGEND (LEO-to-GEO Environment Debris) code to generate a Titan debris cloud. Breakup fragments are created based on the NASA Standard Breakup Model (including fragment size, area-to-mass (A/M), and delta-V distributions). Once fragments are created, they are propagated forward in time with a subroutine GEOPROP. Perturbations included in GEOPROP are those due to solar/lunar gravity, radiation pressure, and major geopotential terms. Barker, et. al, (AMOS Conference Proceedings, 2006, pp. 596-604) used similar LEGEND predictions to correlate survey observations made by MODEST (February 2002) and found several possible night-to-night correlations in the limited survey dataset. One conc lusion of the survey search was to dedicate a MODEST run to observing a GEO region predicted to contain debris fragments and actual Titan debris objects (SSN 25000, 25001 and 30000). Such a dedicated run was undertaken with MODEST between February 17 and 23, 2007 (UT dates). MODEST#s limiting magnitude of 18.0 (S\N approx.10) corresponds to a size of 22cm assuming a diffuse Lambertian albedo of 0.2. However, based on observed break-up data, we expect most debris fragments to be smaller than 22cm which implies a need to increase the effective sensitivity of MODEST for smaller objects. MODEST#s limiting size can be lowered by increasing the exposure time (20 instead of 5 seconds) and applying special image processing. The special processing combines individual CCD images to detect faint objects that are invisible on a single CCD image. Sub-images are cropped from six consecutive CCD images with pixel shifts between images being consistent with the predicted movement of a Titan object. A median image of all the sub-images is then created leaving only those objects with the proper Titan motion. Limiting the median image in this manner brings the needed computer time to process all images taken on one night down to about 50 hours of CPU time.

Barker, E. S.↗
NASA NTRS1998

Effects of Convective Solute and Impurity Transport in Protein Crystal Growth

High-resolution optical interferometry was used to investigate the effects of forced solution convection on the crystal growth kinetics of the model protein lysozyme. Most experiments were conducted with 99.99% pure protein solutions. To study impurity effects, approx. 1% of lysozyme dimer (covalently bound) was added in some cases. We show that the unsteady kinetics, corresponding to bunching of growth steps, can be characterized by the Fourier components of time traces of the growth rate. Specific Fourier spectra are uniquely determined by the solution conditions (composition, temperature, and flow rate) and the growth layer source activity. We found that the average step velocity and growth rate increase by approx. I0% with increasing flow rate, as a result of the enhanced solute supply to the interface. More importantly, faster convective transport results in lower fluctuation amplitudes. This observation supports our rationale for system-dependent effects of transport on the structural perfection of protein crystals. We also found that solution flow rates greater than 500 microns/s result in stronger fluctuations while the average growth rate is decreased. This can lead to growth cessation at low supersaturations. With the intentionally contaminated solutions, these undesirable phenomena occurred at about half the flow rates required in pure solutions. Thus, we conclude that they are due to enhanced convective supply of impurities that are incorporated into the crystal during growth. Furthermore, we found that the impurity effects are reduced at higher crystal growth rates. Since the exposure time of terraces is inversely proportional to the growth rate, this observation suggests that the increased kinetics instability results from impurity adsorption on the interface. Finally, we provide evidence relating earlier observations of "slow protein crystal growth kinetics" to step bunch formation in response to nonsteady step generation.

Vekilov, Peter G.↗
NASA NTRS1997

High Temperature Degradation Mechanisms in Polymer Matrix Composites

Polymer matrix composites are increasingly used in demanding structural applications in which they may be exposed to harsh environments. The durability of such materials is a major concern, potentially limiting both the integrity of the structures and their useful lifetimes. The goal of the current investigation is to develop a mechanism-based model of the chemical degradation which occurs, such that given the external chemical environment and temperatures throughout the laminate, laminate geometry, and ply and/or constituent material properties, we can calculate the concentration of diffusing substances and extent of chemical degradation as functions of time and position throughout the laminate. This objective is met through the development and use of analytical models, coupled to an analysis-driven experimental program which offers both quantitative and qualitative information on the degradation mechanism. Preliminary analyses using coupled diffusion/reaction model are used to gain insight into the physics of the degradation mechanisms and to identify crucial material parameters. An experimental program is defined based on the results of the preliminary analysis which allows the determination of the necessary material coefficients. Thermogravimetric analyses are carried out in nitrogen, air, and oxygen to provide quantitative information on thermal and oxidative reactions. Powdered samples are used to eliminate diffusion effects. Tests in both inert and oxidative environments allow the separation of thermal and oxidative contributions to specimen mass loss. The concentration dependency of the oxidative reactions is determined from the tests in pure oxygen. Short term isothermal tests at different temperatures are carried out on neat resin and unidirectional macroscopic specimens to identify diffusion effects. Mass loss, specimen shrinkage, the formation of degraded surface layers and surface cracking are recorded as functions of exposure time. Geometry effects in the neat resin, and anisotropic diffusion effects in the composites, are identified through the use of specimens with different aspect ratios. The data is used with the model to determine reaction coefficients and effective diffusion coefficients. The empirical and analytical correlations confirm the preliminary model results which suggest that mass loss at lower temperatures is dominated by oxidative reactions and that these reaction are limited by diffusion of oxygen from the surface. The mechanism-based model is able to successfully capture the basic physics of the degradation phenomena under a wide range of test conditions. The analysis-based test design is successful in separating out oxidative, thermal, and diffusion effects to allow the determination of material coefficients. This success confirms the basic picture of the process; however, a more complete understanding of some aspects of the physics are required before truly predictive capability can be achieved.

Cunningham, Ronan A.↗
NASA NTRS1996

High Temperature Degradation Mechanisms in Polymer Matrix Composites

Polymer matrix composites are increasingly used in demanding structural applications in which they may be exposed to harsh environments. The durability of such materials is a major concern, potentially limiting both the integrity of the structures and their useful lifetimes. The goal of the current investigation is to develop a mechanism-based model of the chemical degradation which occurs, such that given the external chemical environment and temperatures throughout the laminate, laminate geometry, and ply and/or constituent material properties, we can calculate the concentration of diffusing substances and extent of chemical degradation as functions of time and position throughout the laminate. This objective is met through the development and use of analytical models, coupled to an analysis-driven experimental program which offers both quantitative and qualitative information on the degradation mechanism. Preliminary analyses using a coupled diffusion/reaction model are used to gain insight into the physics of the degradation mechanisms and to identify crucial material parameters. An experimental program is defined based on the results of the preliminary analysis which allows the determination of the necessary material coefficients. Thermogravimetric analyses are carried out in nitrogen, air, and oxygen to provide quantitative information on thermal and oxidative reactions. Powdered samples are used to eliminate diffusion effects. Tests in both inert and oxidative environments allow the separation of thermal and oxidative contributions to specimen mass loss. The concentration dependency of the oxidative reactions is determined from the tests in pure oxygen. Short term isothermal tests at different temperatures are carried out on neat resin and unidirectional macroscopic specimens to identify diffusion effects. Mass loss, specimen shrinkage, the formation of degraded surface layers and surface cracking are recorded as functions of exposure time. Geometry effects in the neat resin, and anisotropic diffusion effects in the composites, are identified through the use of specimens with different aspect ratios. The data is used with the model to determine reaction coefficients and effective diffusion coefficients. The empirical and analytical correlations confirm the preliminary model results which suggest that mass loss at lower temperatures is dominated by oxidative reactions and that these reaction are limited by diffusion of oxygen from the surface. The mechanism-based model is able to successfully capture the basic physics of the degradation phenomena under a wide range of test conditions. The analysis-based test design is successful in separating out oxidative, thermal, and diffusion effects to allow the determination of material coefficients. This success confirms the basic picture of the process; however, a more complete understanding of some aspects of the physics are required before truly predictive capability can be achieved.

Cunningham, Ronan A.↗
NASA NTRS2009

Cratering Equations for Zinc Orthotitanate Coated Aluminum

The final STS-125 servicing mission (SM4) to the Hubble Space Telescope (HST) in May of 2009 saw the return of the 2nd Wide Field Planetary Camera (WFPC2) aboard the shuttle Discovery. This hardware had been in service on HST since it was installed during the SM1 mission in December of 1993 yielding one of the longest low Earth orbit exposure times (15.4 years) of any returned space hardware. The WFPC2 is equipped with a 0.8 x 2.2 m radiator for thermal control of the camera electronics (Figure 1). The space facing surface of the 4.1 mm thick aluminum radiator is coated with Z93 zinc orthotitanate thermal control paint with a nominal thickness of 0.1 0.2 mm. Post flight inspections of the radiator panel revealed hundreds of micrometeoroid/orbital debris (MMOD) impact craters ranging in size from less than 300 to nearly 1000 microns in diameter. The Z93 paint exhibited large spall areas around the larger impact sites (Figure 2) and the craters observed in the 6061-T651 aluminum had a different shape than those observed in uncoated aluminum. Typical hypervelocity impact craters in aluminum have raised lips around the impact site. The craters in the HST radiator panel had suppressed crater lips, and in some cases multiple craters were present instead of a single individual crater. Humes and Kinard observed similar behavior after the WFPC1 post flight inspection and assumed the Z93 coating was acting like a bumper in a Whipple shield. Similar paint behavior (spall) was also observed by Bland2 during post flight inspection of the International Space Station (ISS) S-Band Antenna Structural Assembly (SASA) in 2008. The SASA, with similar Z93 coated aluminum, was inspected after nearly 4 years of exposure on the ISS. The multi-crater phenomena could be a function of the density, composition, or impact obliquity angle of the impacting particle. For instance, a micrometeoroid particle consisting of loosely bound grains of material could be responsible for creating the multiple craters. Samples were obtained from the HST largest craters for examination by electron microscope equipped with x-ray spectrometers to determine impactor source (micrometeoroid or orbital debris). In an attempt to estimate the MMOD particle diameters that produced these craters, this paper will present equations for spall diameter, crater depth and crater diameter in Z93 coated aluminum. The equations will be based on hypervelocity impact tests of Z93 painted aluminum at the NASA White Sands Test Facility. Equations inputs for velocities beyond the testable regime are expected from hydrocode simulations of Z93 coated aluminum using CTH and ANSYS AUTODYN.

Hyde, James↗
NASA NTRSDate not supplied

Space-qualified Chalcogenide Materials through ISS MISSE Exposure —From Property to Application

In March 2021, twenty-four samples of various phase change materials (PCMs - Ge2Sb2Te5, Ge2Sb2Se4Te1, and Sb2Se3) along with metasurface optical components comprised of these PCMs, were delivered to the International Space Station (ISS) as part of the Materials International Space Station Experiment (MISSE-14) test campaign [1]. Although PCMs have previously been noted for their resilience to various forms of radiation [2], they had not been tested in a realistic space environment until this exposure campaign with joint NASA and MIT collaboration. During the six-month total open exposure time in low earth orbit (LEO), high-resolution cameras scanned and captured photographs of the samples to detect changes as a function of time along with on-orbit measured temperature, UV radiation, total atomic oxygen fluence, and total ionizing radiation doses. The samples were returned to NASA Langley Research Center in March 2022 for post-flight characterization. This duplicated the preflight characterization (i.e., material composition and crystallinity that limits switching speed, index contrast, loss, etc.) conducted before launch. The space sector has witnessed tremendous growth within the past decade—not only from government agencies but also entrants from the private sector. Future growth in the capabilities of Earth observation, deep space, and planetary surface missions using miniaturized spacecraft platforms can only be sustained by innovations in the design of remote sensors and other sub-systems. Active metasurface optics with enhanced tunability and reconfigurability continues to redefine the boundaries of optical science [3]. The introduction of PCM technology and associated optical devices will help to accelerate the adoption of new architectures for reduced size, weight, power, and cost (SWaP-C) platforms in space.Here we introduce results obtained from the MISSE-14 mission related to space qualification of PCM-based optic devices and constituent materials. We then discuss our recent work developing active integrated photonic devices and metasurface optics based on PCMs for space applications. This includes tunable and reconfigurable optical metasurface devices to support NASA space communication and LIDAR applications. PCMs are quickly becoming interesting photonics materials but questions related to mission suitability remain, particularly in regard to key properties like figures-of-merit (FOM, Δn/Δk), glass forming temperatures, and phase transition speeds. This talk will describe efforts to afford researchers the ability to have access to cost-effective data on exposure-induced changes to PCM fundamental physical and optical properties to assess their utility for space applications. The MISSE-14 sample exposure campaign allows a complete understanding of the limitations of the PCMs for various space-based electronic and optoelectronic applications.

Chalcogenide Phase change material↗
NASA NTRS1997

The Solar-Stellar Connection (NAG5-6124: SOHO Guest Investigator Program)

The following is a final report from the SOHO Guest Investigator program to use the SUMER far-UV spectrometer to obtain imaging spectroscopy in support of the goals of the so-called "solar-stellar connection." In particular, a major emphasis was utilization of the long-slit time-resolved maps of the solar surface in bright far-UV emission lines to deduce how particular aspects of the temporally and spatially averaged line profiles trace back to individual structural features of the magnetically disturbed outer atmosphere; to help interpret the unresolved line profiles from high quality stellar observations (say, with the Space Telescope Imaging Spectrograph). The researchers served two tours of duty in the SOHO Operations Center as SUMER planners, during which time we conducted an extensive series of observing programs. These can be divided into three general categories: surface mapping, translimb spectroscopy, and active region diagnostics. We have analyzed some of the large volumes of data to the point where we have presented them in poster papers, and in invited papers at national and international meetings. Listed below are the titles of the preliminary publications we have written, including brief abstracts to indicate the main results. (1) Chromospheric structure and Dynamics-- Observations -- The chromosphere is a highly structured dynamic 'layer' of the solar outer atmosphere. Here, not only are the effects of mechanical heating first evident (moving upward in altitude from the deep photosphere), but also the amount of nonradiative energy deposited is far greater than in the albeit much hotter overlying transition region and corona. Further, the chromosphere is by far the thickest zone of the solar atmosphere with respect to the pressure scale height. A major goal of stellar astrophysics is to understand how the chromosphere is heated and why it adopts its peculiar structure. A cursory examination of solar filtergrams and high-resolution movies demonstrates that much of the chromospheric "action" must be occurring on fine spatial scales and short times; particularly in the cell interior transient brightenings, but also in the longer-lived network fragments. That regime of investigation is far removed from what one usually associates with "synoptic" measurements. Nevertheless, synoptic observations of chromospheric indices, filtergrams, and globally-averaged profile parameters not only can provide important insight concerning the crucial role of the cycle-variable part of the solar magnetic field; but they also can forge a key link with analogous measurements of the stars, where often the phenomena can be significantly exaggerated from the solar case, but high spatial resolution reconnaissance is not even a remote possibility. In addition to discussing the synoptic aspects of chromospheric structure and dynamics, I summarized new insights into the general problem of the solar chromosphere that have been obtained recently with the SUMER far-ultraviolet spectrometer on SOHO. (2) CO and the Temperature Structure of the Solar Atmosphere -- The surface layers of the Sun provide a crucial boundary condition for many of the processes that occur in the deep interior. The stratification of the outer solar atmosphere once was thought to be well understood. However, studies of thermally sensitive molecular absorptions in the infrared revealed puzzling anomalies. Strong lines of the CO fundamental vibration-rotation bands near 5 microns showed very cool temperatures at the extreme limb, and remarkable off-limb emissions extending well into the supposedly hot chromosphere. The conflicting pictures of the photosphere/chromosphere interface, from the widely separated wavelength regimes, has raised suspicions that those "layers" of the atmosphere are much more inhomogeneous than previously suspected. One proposal is that the low chromosphere is dominated by cool gas, the "COmosphere," which is threaded by a network of persistent small-scale hot magnetic filaments and occasionally disrupted by localized acoustic disturbances. The COmosphere is capped by the merged fields of the network elements in the chromospheric "canopy." (3) Translimb Spectroscopy with SOHO/SUMER -- We have used SUMER to obtain deep exposures of the 1300-1400 A spectrum, at the extreme limb and off-limb. Previous "translimb" studies in the thermal infrared had revealed remarkable extensions of cold material (T is approximately equal to 3000 K)-traced by carbon monoxide emission lines-into the heart of the hot chromosphere. A main objective of our program was to search for corresponding far-UV signatures of the "thermally-bifurcated" low chromosphere; for example, radiatively fluoresced emissions of the CO A-X 4th-positive system (collisional excitation would be negligible in cold gas). We conducted two separate observing programs with SUMER. Both made use of the 1 inch-diameter circular aperture, translated across the limb in the minimum motor step increments of 0."375, along the central meridian in the Northern polar coronal hole. The first program executed for nine hours beginning 19UT 25 Oct 1996. The full wavelength range was 1340-1400 A. It was recorded in two overlapping segments, placing key regions of the spectrum alternately on the KBr and bare parts of the detector, to help isolate 2nd-order features. Each segment was integrated for 500 s, and 32 pairs were obtained to span a 12" swath centered on the optical limb. The second program was conducted 00-09UT 01 Dec 1996. It consisted of a single wavelength setting (1300-1340 A) with exposure time 500 s, but twice the spatial coverage of the earlier series: 64 steps, for a total displacement of 24". The strong chromospheric resonance lines of atomic oxygen (1302-1305 A) and ionized carbon (1334-1335 A) were observed on the bare part of the MCP camera.

Ayres, Thomas R.↗
NASA NTRS1969

Improved high-temperature-strength nickel-base superalloy

Nickel-base superalloy has a strength of 20,000 psi at 2,200 degrees F, approximately double the strength of the strongest available cast nickel-base alloys. It is not subject to the formation of embrittling phases upon long time exposure at intermediate temperatures.

Freche, J. C.↗
NASA NTRS1969

Are cosmic electrons anisotropic?

Anisotropy of relativistic cosmic ray electrons, considering electron exposure time to synchrotron effects, energy loss from inverse Compton effect, etc

Earl, J. A.↗
NASA NTRS1970

Optical contamination during thermal testing in vacuum

Comparative tests are described for optical degradation in vacuum systems served by oil-type or ion-type pumping operation. Results show that degradation occurs only during ultraviolet irradiation in vacuum systems with oil-type pumping systems and that it increases with exposure time. Degradation does not occur with ion systems.

Zwiener, J. M.↗