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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS1998

Using an Ongoing Study of Terrestrial Plant Response to Ultraviolet Radiation in Project ALERT

The ALERT (Augmented Learning Environment for Renewable Teaching) Project is a cooperative California-based program with two main partners: California State University (CSU) geoscience and education departments and two NASA Centers, the Jet Propulsion Laboratory (JPL) in Pasadena and the Ames Research Center (ARC) in Mountain View. This paper presents an example of how a NASA research effort can be used in the undergraduate classroom. A study, now in the fourth year, subjects test plants to exposures of varying solar ultraviolet (UV) radiation (280 - 340 nm); a full solar UV exposure, a solar UV exposure less about 14% of ambient UV flux, and a UV-blocked regime. This experiment is simple in that only modest amounts of expense are required yet it is elegant since only one variable, UV-flux is involved. The experiment lends itself to teaching several of the Earth Sciences because it uses information from botany, taxonomy, and ecology. Aspects of physics are inherent in the study since portions of the electromagnetic spectrum are studied. Further, since only one of many variables are manipulated, UV flux, the study demonstrates how the scientific method is used in formulating and testing hypotheses. Based on the ALERT experience this summer, this study will be implemented at a CSU campus with the expectation that it will serve as a pedagogical tool and where it will involve students in actual research.

Condon, Estelle↗
NASA NTRS1994

The effect of Low Earth Orbit exposure on some experimental fluorine and silicon-containing polymers

Several experimental fluorine and silicon-containing polymers in film form were exposed to low Earth orbit (LEO) on a Space Shuttle flight experiment (STS-46, Evaluation of Oxygen Interaction with Materials, EOIM-3). The environmental parameters of primary concern were atomic oxygen (AO) and ultraviolet (UV) radiation. The materials were exposed to 2.3 plus or minus 0.1 x 10(exp 20) oxygen atoms/sq cm and 30.6 UV sun hours during the flight. In some cases, the samples were exposed at ambient, 120 C and 200 C. The effects of exposure on these materials were assessed utilizing a variety of characterization techniques including optical, scanning electron (SEM) and scanning tunneling (STM) microscopy, UV-visible (UV-VIS) transmission, diffuse reflectance infrared (DR-FTIR), x-ray photoelectron (XPS) spectroscopy, and in a few cases, gel permeation chromatography (GPC). In addition, weight losses of the films, presumably due to AO erosion, were measured. The fluorine-containing polymers exhibited significant AO erosion and exposed films were diffuse or 'frosted' in appearance and consequently displayed dramatic reductions in optical transmission. The silicon-containing films exhibited minimum AO erosion and the optical transmission of exposed films was essentially unchanged. The silicon near the exposed surface in the films was converted to silicate/silicon oxide upon AO exposure which subsequently provided protection for the underlying material. The silicon-containing epoxies are potentially useful as AO resistant coatings and matrix resins as they are readily processed into carbon fiber reinforced composites and cured via electron radiation.

Connell, John W.↗
NASA NTRS2015

Anti-Adhesion Elastomer Seal Coatings for Ultraviolet and Atomic Oxygen Protection

Radiation blocking sunscreen coatings have been developed for the protection of elastomer seals used in low-Earth-orbit (LEO). The coatings protect the seals from ultraviolet (UV) radiation and atomic oxygen (AO) damage. The coatings were developed for use on NASA docking seals. Docking seal damage from the UV and AO present in LEO can constrain mission time-line, flight mode options, and increases risk. A low level of adhesion is also required for docking seals so undocking push-off forces can be low. The coatings presented also mitigate this unwanted adhesion. Greases with low collected volatile condensable materials (CVCM) and low total mass loss (TML) were mixed with slippery and/or UV blocking powders to create the protective coatings. Coatings were applied at rates up to 2 milligrams per square centimeter. Coated seals were exposed to AO and UV in the NUV (near-UV) and UV-C wavelength ranges (300 to 400 nanometers and 254 nanometers, respectively). Ground based ashers were used to simulate the AO of space. The Sun's UV energy was mimicked assuming a nose forward flight mode, resulting in an exposure rate of 2.5 megajoules per square meter per day. Exposures between 0 and 147 megajoules per square meter (UV-C) and 245 megajoules per square meter (NUV) were accomplished. The protective coatings were durable, providing protection from UV after a simulated docking and undocking cycle. The level of protection begins to decline at coverage rates less than 0.9 milligrams per square centimeter. The leakage of seals coated with Braycote plus 20 percent Z-cote ZnO sunscreen increased by a factor of 40 after moderate AO exposure; indicating that this coating might not be suitable due to AO intolerance. Seals coated with DC-7-16.4 percent Z-cote ZnO sunscreen were not significantly affected by combined doses of 2 x 10 (sup 21) atoms per square AO with 73 megajoules per square meter UV-C. Unprotected seals were significantly damaged at UV-C exposures of 0.3 megajoules per square meter and DC-7-16.4 percent Z-cote coated seals were undamaged at all exposures up to the limits tested thus far which were 147 megajoules per square meter UV-C and 245 megajoules per square meter NUV. The coatings decreased adhesion sufficiently for docking seals at temperatures equal to or greater than -8 degrees Centigrade thus offer a simple and inexpensive way to mitigate adhesion.

adhesion↗
NASA NTRS1982

IUS materials outgassing condensation effects on sensitive spacecraft surfaces

Four materials used on the inertial upper state (IUS) were subjected to vacuum conditions and heated to near-operational temperatures (93 to 316 C), releasing volatile materials. A fraction of the volatile materials were collected on 25 C solar cells, optical solar reflectors (OSR's) or aluminized Mylar. The contaminated surfaces were exposed to 26 equivalent sun hours of simulated solar ultraviolet (UV) radiation. Measurements of contamination deposit mass, structure, reflectance and effects on solar cell power output were made before and after UV irradiation. Standard total mass loss - volatile condensible materials (TML - VCM) tests were also performed. A 2500 A thick contaminant layer produced by EPDM rubber motor-case insulation outgassing increased the solar absorptance of the OSR's from 0.07 to 0.14, and to 0.18 after UV exposure. An 83,000 A layer caused an increase from 0.07 to 0.21, and then the 0.46 after UV exposure. The Kevlar-epoxy motor-case material outgassing condensation raised the absorptance from 0.07 to 0.13, but UV had no effect. Outgassing from multilayer insulation and carbon-carbon nozzle materials did not affect the solar absorptance of the OSR's.

Mullen, C. R.↗
DOE OSTI2020

Galaxy Cluster Contribution to the Diffuse Extragalactic Ultraviolet Background

The diffuse ultraviolet background radiation has been mapped over most of the sky with 2′ resolution using data from the Galaxy Evolution Explorer survey. We utilize this map to study the correlation between the UV background and clusters of galaxies discovered via the Sunyaev–Zeldovich effect in the Planck survey. We use only high Galactic latitude (|b|>60{sup ∘}) galaxy clusters to avoid contamination by Galactic foregrounds, and we only analyze clusters with a measured redshift. This leaves us with a sample of 142 clusters over the redshift range of 0.02 ≤ z ≤ 0.72, which we further subdivide into four redshift bins. In analyzing our stacked samples binned by redshift, we find evidence for a central excess of UV background light compared to local backgrounds for clusters with z < 0.3. We then stacked these z < 0.3 clusters to find a statistically significant excess of 12 ± 2.3 photon cm{sup −2} s{sup −1} sr{sup −1} Å{sup −1} over the median of ∼380 photon cm{sup −2} s{sup −1} sr{sup −1} Å{sup −1} measured around random blank fields. We measure the stacked radial profile of these clusters, and find that the excess UV radiation decays to the level of the background at a radius of ∼1 Mpc, roughly consistent with the maximum radial extent of the clusters. Analysis of possible physical processes contributing to the excess UV brightness indicates that non-thermal emission from relativistic electrons in the intracluster medium and faint, unresolved UV emission from cluster member galaxies and intracluster light are likely the dominant contributors.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1990

H2 line emission in three Seyfert nuclei: Evidence against UV-excitation

Line emission from vibrationally excited molecular hydrogen has been detected in a considerable number of active galactic nuclei (AGNs), including those generally believed to contain compact and luminous central engines (e.g., Seyfert nuclei) and those in which the luminosity is believed to arise from massive bursts of star formation (starburst nuclei). In most of these AGNs, only the bright 1-0 S(1) line (rest wavelength 2.12 microns) has been searched for and detected to date. Line-emitting H2 can be excited directly either by energetic collisions created by shock waves or by absorption of UV radiation. Each of these excitation mechanisms has been clearly identified in galactic and extragalactic regions. In active galactic nuclei strong sources of UV and (in some case) x rays are present. If the nuclear molecular matter is quiescent (i.e., isolated from the active nucleus and not set into motion by episodes of star formation) the H2 line emission will be dominated by fluorescence, or possibly by thermal emission due to heating by x rays (Krolik, this conference). However, it is expected or indeed observed that a significant fraction of the interstellar medium in and near these nuclei is undergoing rapid motions; either generated by the central engine or by a nuclear starburst, which are capable of producing strong shock phenomena in nearby molecular gas. Thus, a priori it is not obvious which mechanism is responsible for the H2 line emission from the nucleus of an active galaxy.

Geballe, T. R.↗
NASA NTRS2002

The Laboratory Production of Complex Organic Molecules in Simulated Interstellar Ices

Much of the volatiles in interstellar dense clouds exist in ices surrounding dust grains. Their low temperatures preclude most chemical reactions, but ionizing radiation can drive reactions that produce a suite of new species, many of which are complex organics. The Astrochemistry Lab at NASA Ames studies the UV radiation processing of interstellar ice analogs to better identify the resulting products and establish links between interstellar chemistry, the organics in meteorites, and the origin of life on Earth. Once identified, the spectral properties of the products can be quantified to assist with the search for these species in space. Of particular interest are findings that UV irradiation of interstellar ice analogs produces molecules of importance in current living organisms, including quinones, amphiphiles, and amino acids.

Dworkin, J. P.↗
NASA NTRS1987

High-resolution spectroscopy of the z = 1.79 absorption-line system toward B2 1225 + 317

The results of Multiple Mirror Telescope echelle spectroscope scans of species in the z = 1.79 system toward the quasar B2 1225 + 317 are reported. The campaign was undertaken to compare quasar absorption-line systems with gas absorption lines in other galaxies. Relative column densities obtained for Zn II, Si II, Mg II, Fe II and H I were similar to those observed for the interstellar medium. Data analyses with photoionization models for the radiation field above the Lyman limit yielded upper and lower limits to the specific intensity at 1000 A that were consistent with the UV radiation field in the halo of a spiral galaxy.

Bechtold, Jill↗
NASA NTRS1992

Estimation of the end-of-life optical properties of Z-93 thermal control coating for the Space Station Freedom

This paper describes an approach to estimating the 30-year end-of-life optical properties of Z-93 white, thermal control coating on the Space Station Freedom. Estimations of the 30-year end-of-life properties of thermal control coatings are necessary for sizing the thermal radiators. The available flight and ground data and computer generated contamination models are used to predict the effects of ground handling, exposure to UV radiation, and on-orbit contamination on the optical properties of Z-93. The solar absorptance for portions of the thermal control system radiator surfaces is predicted to change from 0.15 to 0.36 after 30 years of low earth orbit environmental exposure. The infrared emittance is predicted to change from 0.92 to 0.90.

Hasegawa, Mark M.↗
NASA NTRS2004

Short Time Scale Evolution of Microbiolites in Rapidly Receding Altiplanic Lakes: Learning How to Recognize Changing Signatures of Life

As part of the exploration of high altitude lakes as analogs to Martian paleolakes environment, we are investigating a remarkably large and diverse field of lacustrine stromatolites located at 4,365m in the Bolivian Altiplano (22 deg 47 00 min S and 67 deg 47.00 min W).The field is composed of both early Holocene fossil structures located on paleoshorelines and present-day active cyanobacterial communities on the shore and at the bottom of the current Laguna Blanca and Verde. Its physical environment, broad diversity of morphologies, and their associated spatial heterogeneity, origin, and scale offer a unique opportunity to explore microbiolites in conditions reminiscent of early Earth and Mars. At this altitude and latitude, UV radiation levels are enhanced (40% higher than sea level) and harmful to microorganisms living in shallow waters which provide only minimal protection from UV. Similar conditions prevailed on early Earth when the ozone layer had yet to be formed in the atmosphere. Compared to those studied at sea levels, these stromatolites could yield new insights about the earliest terrestrial forms of life. Moreover, the combination of physical and geological environment of this site is exceptionally analogous to conditions believed to be prevalent on Mars at the end of the Noachian (3.5 Ga ago), allowing to test the potential for forming stromatolites in martian paleolakes and learn how to identify their fossil record remotely. Our overarching goal is to generate new astrobiological information on high-altitude stromatolites as clues to early biospheres with implications for Earth and Mars. Our two central objectives are: (1) characterize the biological, geological, and mineralogical features and significance of this field, and to identify geo-signatures such as morphology, geology, chronostratigraphy, mineralogy and biosignatures, and (2) to facilitate remote-sensing and ground robotic detection capabilities for future astrobiological missions to Mars.

Cabrol, N. A.↗
NASA NTRS2002

The Laboratory Production of Complex Organic Molecules in Simulated Interstellar Ices

Much of the volatiles in interstellar dense clouds exist in ices surrounding dust grains. Their low temperatures preclude most chemical reactions, but ionizing radiation can drive reactions that produce a suite of new species, many of which are complex organics. The Astrochemistry Lab at NASA-Ames studies the UV radiation processing of interstellar ice analogs to better identify the resulting products and establish links between interstellar chemistry, the organics in meteorites, and the origin of life on Earth. Once identified, the spectral properties of the products can be quantified to assist with the search for these species in space. Of particular interest are findings that UV irradiation of interstellar ice analogs produces molecules of importance in current living organisms, including quiriones, amphiphiles, and amino acids. Quinones play a variety of roles including electron transport and are used by all organisms. Studies show that quinones should be made wherever polycyclic aromatic hydrocarbons are irradiated in interstellar ices (Bernstein et al. 2001). Amphiphiles are also made when mixed molecular ices are irradiated. These amphiphiles self-assemble into membrane-walled vesicles when put in liquid water (Dworkin et al. 2001). Ice irradiation can also produce (Bernstein et al. 2002) and destroy amino acids (Ehrenfreund et al. 2001). Many of the same processes thought to make organics in space should yield products highly enriched in deuterium (D) (Sandford et al. 2001). The high D/H ratios in some interstellar species, and the knowledge that many of the organics in primitive meteorites are D-enriched, suggests that such linkages do exist. By using D as a tracer, we expect to learn more about the different chemical processes occurring in space and their relative importance in the production of different organic compounds and delivery to planetary surfaces.

Dworkin, Jason P.↗
NASA NTRS1991

Non-LTE models of Titan's upper atmosphere

Models for the thermal structure of Titan's upper atmosphere, between 0.1 mbar and 0.01 nbar are presented. The calculations include non-LTE heating/cooling in the rotation-vibration bands of CH4, C2H2, and C2H6, absorption of solar IR radiation in the near-IR bands of CH4 and subsequent cascading to the nu-4 band of CH4, absorption of solar EUV and UV radiation, thermal conduction and cooling by HCN rotational lines. Unlike earlier models, the calculated exospheric temperature agrees well with observations, because of the importance of HCN cooling. The calculations predict a well-developed mesopause with a temperature of 135-140 K at an altitude of approximately 600 km and pressure of about 0.1 microbar. The mesopause is at a higher pressure than predicted by earlier calculations because non-LTE radiative transfer in the rotation-vibration bands of CH4, C2H2, and C2H6 is treated in an accurate manner. The accuracy of the LTE approximation for source functions and heating rates is discussed.

Yelle, Roger V.↗
NASA NTRS2000

Simulated Space Environmental Testing on Thin Films

An exploratory program has been conducted, to irradiate some mature commercial and some experimental polymer films with radiation simulating certain Earth orbits, and to obtain data about the response of each test film's reflective and tensile properties. Protocols to conduct optimized tests were considered and developed to a "prototype" level during this program. Fifteen polymer film specimens were arranged on a specially designed test fixture. The fixture featured controlled exposure areas, and protected the ends of the samples for later gripping in tensile tests. The fixture featured controlled exposure areas, and protected the ends of the samples for later gripping in tensile tests. The fixture containing the films was installed in a clean vacuum chamber where protons, electrons and solar ultraviolet (UV) radiation could simultaneously irradiate the specimens. Near realtime UV rates were used, whereas proton and electron rates were accelerated appreciably to simulate 5 years in orbit during a two month test. Periodically, the spectral reflectance of each film was measured in situ. After the end of the irradiation, final reflectance measurements were made in situ, and solar absorptance values were derived for each specimen. These samples were then measured in air for thermal emittance and for tensile strength. Most specimens withstood the irradiation intact, but with reduced reflectance (increased solar absorptance). Thermal emittance changed slightly in several materials, as did their tensile strength and elongation at break. Conclusions are drawn about the performance of the films. Simulated testing to an expected 5 year dose of electrons and protons consistent with those expected at L2 and 0.98 AU orbits and 100 equivalent solar hours exposure.

Russell, Dennis A.↗
DOE OSTI2021

Improvement of the Biosynthesis of Resveratrol in Endophytic Fungus (Alternaria sp. MG1) by the Synergistic Effect of UV Light and Oligomeric Proanthocyanidins

Resveratrol, a natural polyphenol compound with multiple bioactivities, is widely used in food and pharmaceutical industry. Endophytic fungus Alternaria sp. MG1, as a native producer of resveratrol, shows increasing potential application. However, strategies for improvement of the biosynthesis of resveratrol in this species are still scarce. In this study, different elicitors were used to investigate their effect on the biosynthesis of resveratrol in MG1 and the induction mechanism. Ultrasound and sodium butyrate had no effect and slight inhibition on the resveratrol production and related gene expression, respectively. UV radiation and co-culture with Phomopsis sp. XP-8 significantly promoted the biosynthesis of resveratrol with the highest production (240.57μg/l) coming from UV 20min. Co-culture altered the profiles of secondary metabolites in MG1 by promoting and inhibiting the synthesis of stilbene and lignin compounds, respectively, and generating new flavonoids ((+/−)-taxifolin, naringin, and (+)-catechin). Oligomeric proanthocyanidins (OPC) also showed an obviously positive influence, leading to an increase in resveratrol production by 10 to 60%. Two calcium-dependent protein kinases (CDPK) were identified, of which CDPK1 was found to be an important regulatory factor of OPC induction. Synergistic treatment of UV 20min and 100μm OPC increased the production of resveratrol by 70.37% compared to control and finally reached 276.31μg/l.

Lu, Yao↗
NASA NTRS1989

Evaluation of atomic oxygen resistant protective coatings for fiberglass-epoxy composites in LEO

Fiberglass-epoxy composite masts are the prime structural members for the Space Station Freedom solar array. At the altitude where Space Station Freedom will operate, atomic oxygen atoms are the most predominant species. Atomic oxygen is highly reactive and has been shown to oxidize organic and some metallic materials. Tests with random and directed atomic oxygen exposure have shown that the epoxy is removed from the composite exposing brittle glass fibers which could be easily removed from the surface where they could contaminate Space Station Freedom Systems. Protection or fiber containment systems; inorganic based paints, aluminum braid, and a metal coating; were evaluated for resistance to atomic oxygen, vacuum ultraviolet radiation, thermal cycling, and mechanical flexing. All appeared to protect well against atomic oxygen and provide fiber containment except for the single aluminum braid covering. UV radiation resistance was acceptable and in general, thermal cycling and flexure had little to no effect on the mass loss rate for most coatings.

Rutledge, Sharon K.↗
NASA NTRS1989

Evaluation of atomic oxygen resistant protective coatings for fiberglass-epoxy composites in LEO

Fiberglass-epoxy composite masts are the prime structural members for the Space Station Freedom solar array. At the altitude where Space Station Freedom will operate, atomic oxygen atoms are the most predominant species. Atomic oxygen is highly reactive and has been shown to oxidize organic and some metallic materials. Tests with random and directed atomic oxygen exposure have shown that the epoxy is removed from the composite exposing brittle glass fibers which could be easily removed from the surface where they could contaminate space Station Freedom Systems. Protection or fiber containment systems, inorganic based paints, aluminum braid, and a metal coatinsg, were evaluated for resistance to atomic oxygen, vacuum ultraviolet radiation, thermal cycling, and mechanical flexing. All appeared to protect well against atomic oxygen and provide fiber containment except for the single aluminum braid covering. UV radiation resistance was acceptable and in general, thermal cycling and flexure had little to no effect on the mass loss rate for most coatings.

Rutledge, Sharon K.↗
NASA NTRS1990

Analysis of satellite data to deduce stratospheric constituents and UV spectroscopic properties of the atmosphere

The objective is to better understand the stratosphere, its constituents, and its ultraviolet optical properties, through detailed analysis of data from the SBUV instrument on Nimbus 7 and comparison with data from other instruments, including the NOAA 9 SBUV 2, SAGE, SME, and SMM. One conclusion to be drawn from the Ozone Trends Panel report is that there are unresolved differences in the ozone profiles measured by different instruments. While the purpose of the work is more to understand the details of the UV radiation field in the stratosphere than it is to assess the accuracy of the SBUV ozone measurement itself, improved understanding of specific problems in the UV will lead to more accurate ozone retrievals. Areas of study include the effect of aerosols on the backscattered albedo, the shape of the ozone profile near the stratopause, the effect of possible polar mesospheric clouds, and the measureability of nitric oxide and sulfur dioxide.

Mcpeters, Richard D.↗