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NASA NTRS2000

The Effect of Low Earth Orbit Atomic Oxygen Exposure on Phenylphosphine Oxide-Containing Polymers

Thin films of phenylphosphine oxide-containing polymers were exposed to low Earth orbit aboard a space shuttle flight (STS-85) as part of flight experiment designated Evaluation of Space Environment and Effects on Materials (ESEM). This flight experiment was a cooperative effort between the NASA Langley Research Center (LaRC) and the National Space Development Agency of Japan (NASDA). The thin film samples described herein were part of an atomic oxygen exposure experiment (AOE) and were exposed to primarily atomic oxygen (~1 X 1019 atoms/cm2). The thin film samples consisted of three phosphine oxide containing polymers (arylene ether, benzimidazole and imide). Based on post-flight analyses using atomic force microscopy, X-ray photoelectron spectroscopy, and weight loss data, it was found that atomic oxygen exposure of these materials efficiently produces a phosphate layer at the surface of the samples. This layer provides a barrier towards further attack by AO. Consequently, these materials do not exhibit linear erosion rates which is in contrast with most organic polymers. Qualitatively, the results obtained from these analyses compare favorably with those obtained from samples exposed to atomic oxygen and or oxygen plasma in ground based exposure experiments. The results of the low Earth orbit atomic oxygen exposure on these materials will be compared with those of ground based exposure to AO.

Connell, John W.↗

NASA NTRS2002

Solid state 31phosphorus nuclear magnetic resonance of iron-, manganese-, and copper-containing synthetic hydroxyapatites

The incorporation of micronutrients into synthetic hydroxyapatite (SHA) is proposed for slow release of these nutrients to crops in the National Aeronautics and Space Administration's (NASA's) Advanced Life Support (ALS) program for Lunar or Martian outposts. Solid state 31P nuclear magnetic resonance (NMR) was utilized to examine the paramagnetic effects of Fe3+, Mn2+, and Cu2+ to determine if they were incorporated into the SHA structure. Separate Fe3+, Mn2+, and Cu2+ containing SHA materials along with a transition metal free SHA (pure-SHA) were synthesized using a precipitation method. The proximity (<1 nm) of the transition metals to the 31P nuclei of SHA were apparent when comparing the integrated 31P signal intensities of the pure-SHA (87 arbitrary units g-1) with the Fe-, Mn-, and Cu-SHA materials (37-71 arbitrary units g-1). The lower integrated 31P signal intensities of the Fe-, Mn-, and Cu-SHA materials relative to the pure-SHA suggested that Fe3+, Mn2+, and Cu2+ were incorporated in the SHA structure. Further support for Fe3+, Mn2+, and Cu2+ incorporation was demonstrated by the reduced spin-lattice relaxation constants of the Fe-, Mn-, and Cu-SHA materials (T'=0.075-0.434s) relative to pure-SHA (T1=58.4s). Inversion recovery spectra indicated that Fe3+, Mn2+, and Cu2+ were not homogeneously distributed about the 31P nuclei in the SHA structure. Extraction with diethylene-triamine-penta-acetic acid (DTPA) suggested that between 50 and 80% of the total starting metal concentrations were incorporated in the SHA structure. Iron-, Mn-, and Cu-containing SHA are potential slow release sources of Fe, Mn, and Cu in the ALS cropping system.

NASA Discipline Life Support Systems↗

NASA NTRS2000

In vitro evolution of a ribozyme that contains 5-bromouridine

The Tetrahymena group I ribozyme was modified by replacing all 99 component uridine residues with 5-bromouridine. This resulted in a 13-fold reduction in catalytic efficiency in the RNA-catalyzed phosphoester-transfer reaction compared to the behavior of the unmodified ribozyme. A population of 10(13) variant ribozymes was constructed, each containing 5-bromouridine in place of uridine. Five successive 'generations' of in vitro evolution were carried out, selecting for improved phosphoester transferase activity. The evolved molecules exhibited a 27-fold increase in catalytic efficiency compared to the wild-type bromouridine-containing ribozyme, even exceeding that of the wild-type ribozyme in the non-brominated form. Three specific mutations were found to be responsible for this altered behavior. These mutations enhanced activity in the context of 5-bromouridine, but were detrimental in the context of unmodified uridine. The evolved RNAs not only tolerated but came to exploit the presence of the nucleotide analogue in carrying out their catalytic function.

NASA Discipline Exobiology↗

NASA NTRS2000

Synthetic spectra of simulated terrestrial atmospheres containing possible biomarker gases

NASA's proposed Terrestrial Planet Finder, a space-based interferometer, will eventually allow spectroscopic analyses of the atmospheres of extrasolar planets. Such analyses would provide information about the existence of life on these planets. One strategy in the search for life is to look for evidence of O3 (and hence O2) in a planet's atmosphere; another is to look for gases that might be present in an atmosphere analogous to that of the inhabited early Earth. In order to investigate these possibilities, we have calculated synthetic spectra for several hypothetical terrestrial-type atmospheres. The model atmospheres represent four different scenarios. The first two, representing inhabited terrestrial planets, are an Earth-like atmosphere containing variable amounts of oxygen and an early Earth-type atmosphere containing methane. In addition, two cases representing Mars-like and early Venus-like atmospheres were evaluated, to provide possible "false positive" spectra. The calculated spectra suggest that ozone could be detected by an instrument like Terrestrial Planet Finder if the O2 concentration in the planet's atmosphere is > or = 200 ppm, or 10(-3) times the present atmospheric level. Methane should be observable on an early-Earth type planet if it is present in concentrations of 100 ppm or more. Methane has both biogenic and abiogenic sources, but concentrations exceeding 1000 ppm, or 0.1% by volume, would be difficult to produce from abiogenic sources alone. High methane concentrations in a planet's atmosphere are therefore another potential indicator for extraterrestrial life.

NASA Discipline Exobiology↗

NASA NTRS1986

Do the higher oxidation states of the photosynthetic O2-evolving system contain bound H2O?

A modified mass spectrometer was used to determine whether the higher oxidation states of the photosynthetic O2-evolving system contain substrate water that is not freely exchangeable with the external medium. Our data indicated that the higher oxidation states contain no appreciable bound, non-exchangeable H2O. This suggests that H2O oxidation takes place via a rapid, concerted, all-or-none mechanism rather than by a mechanism involving stable, partially oxidized, H2O-derived intermediates. These findings set definite constraints on possible mechanisms of O2 evolution.

NASA Discipline Life Support Systems↗

NASA NTRS2001

The sugar model: catalytic flow reactor dynamics of pyruvaldehyde synthesis from triose catalyzed by poly-l-lysine contained in a dialyzer

The formation of pyruvaldehyde from triose sugars was catalyzed by poly-l-lysine contained in a small dialyzer with a 100 molecular weight cut off (100 MWCO) suspended in a much larger triose substrate reservoir at pH 5.5 and 40 degrees C. The polylysine confined in the dialyzer functioned as a catalytic flow reactor that constantly brought in triose from the substrate reservoir by diffusion to offset the drop in triose concentration within the reactor caused by its conversion to pyruvaldehyde. The catalytic polylysine solution (400 mM, 0.35 mL) within the dialyzer generated pyruvaldehyde with a synthetic intensity (rate/volume) that was 3400 times greater than that of the triose substrate solution (12 mM, 120 mL) outside the dialyzer. Under the given conditions the final yield of pyruvaldehyde was greater than twice the weight of the polylysine catalyst. During the reaction the polylysine catalyst was poisoned presumably by reaction of its amino groups with aldehyde reactants and products. Similar results were obtained using a dialyzer with a 500 MWCO. The dialyzer method of catalyst containment was selected because it provides a simple and easily manipulated experimental system for studying the dynamics and evolutionary development of confined autocatalytic processes related to the origin of life under anaerobic conditions.

Biogenesis↗

NASA NTRS1996

Use-dependent loss of active sympathetic neurogenic vasodilation after nitric oxide synthase inhibition in conscious rats. Evidence for the presence of preformed stores of nitric oxide-containing factors

In this study, we examined whether air-jet stress-induced active sympathetic hindlimb vasodilation in conscious rats involves the release of preformed stores of nitric oxide-containing factors. We determined the effects of repeated episodes of air-jet stress (six episodes given 5 minutes apart) on mean arterial pressure and vascular resistances in the mesenteric bed and intact and sympathetically denervated hindlimb beds of conscious rats treated with saline or the nitric oxide synthesis inhibitor N omega-nitro-L-arginine methyl ester (L-NAME, 25 mumol/kg IV). In saline-treated rats, air-jet stress produced alerting behavior, minor changes in blood pressure, pronounced mesenteric vaso-constriction, and immediate and marked vasodilation in the sympathetically intact hindlimb but a minor vasodilation in the sympathetically denervated hindlimb. Each air-jet stress produced virtually identical responses. In L-NAME-treated rats, the first air-jet stress produced vasodilator responses in the sympathetically intact and sympathetically denervated hindlimbs that were similar to those in the saline-treated rats. However, each subsequent air-jet stress produced progressively smaller vasodilator responses in the sympathetically intact but not the sympathetically denervated hindlimb. There was no loss of air-jet stress-induced alerting behavior or mesenteric vasoconstriction, suggesting that L-NAME did not interfere with the central processing of the air-jet or the resultant changes in autonomic nerve activity. The progressive diminution of air-jet stress-induced vasodilation in the intact hindlimb of L-NAME-treated rats may be due to the use-dependent depletion of preformed stores of nitric oxide-containing factors that cannot be replenished in the absence of nitric oxide synthesis.

NASA Discipline Regulatory Physiology↗

NASA NTRS1996

Impact Properties of Metal Fan Containment Materials Being Evaluated for the High-Speed Civil Transport (HSCT)

Under the Enabling Propulsion Materials (EPM) program - a partnership between NASA, Pratt & Whitney, and GE Aircraft Engines - the Materials and Structures Divisions of the NASA Lewis Research Center are involved in developing a fan-containment system for the High-Speed Civil Transport (HSCT). The program calls for a baseline system to be designed by the end of 1995, with subsequent testing of innovative concepts. Five metal candidate materials are currently being evaluated for the baseline system in the Structures Division's Ballistic Impact Facility. This facility was developed to provide the EPM program with cost-efficient and timely impact test data. At the facility, material specimens are impacted at speeds up to 350 m/sec by projectiles of various sizes and shapes to assess the specimens' ability to absorb energy and withstand impact. The tests can be conducted at either room or elevated temperatures. Posttest metallographic analysis is conducted to improve understanding of the failure modes. A dynamic finite element program is used to simulate the events and both guide the testing as well as aid in designing the fan-containment system.

Source record↗

NASA NTRS2004

Preparation of Proton Exchange Membranes and Lithium Batteries from Melamine-containing Ormosils

Our laboratory has recently reported a series of rodcoil polymers for lithium batteries that display dimensionally stable films with good ionic conductivity. The rod segments consist of rigid linear and branched polyimides and the coil segments are polyethylene oxides (PEO). It has been proposed that good mechanical and transport properties are due to phase separation between the rod and coil segments. It was also observed that increased branching and molecular weight lead to increased conductivity. The following study was undertaken to assess the effects of phase separation in polyalkylene oxides connected by melamine linkages. Melamine was chosen as the linking unit because it provides a branching site, cation binding sites to help ionic transport between polymer chains, and the opportunity for self assembly through hydrogen bonding. Polymers were made by the reaction of cyanuric chloride with a series of amine-terminated alkylene oxides. A linear polymer was first made, followed by reaction of the third site on cyanuric chloride with varying ratios of monofunctional Jeffamine and (3-aminopropyl)triethoxysilane. The lithium trifluoromethane sulfonamide-doped polymers are then crosslinked through a sol-gel process to form free-standing films. Initial results have shown mechanically strong films with lithium conductivities on the order of 2 x 10(exp -5) S/cm at ambient temperature. In a separate study, organically modified silanes (Ormosils) that contain sulfonic acid derivatized melamines have been incorporated into proton exchange membranes. The membranes are made by reaction of the primary amine groups of various ratios of melamine derivative and difunctional Jeffamine (MW = 2000) with the epoxide group of (3-Glycidyloxypropyl)trimethoxysilane. The films were then cross-linked through a sol-gel process. Resulting sulfuric acid doped films are strong, flexible, and have proton conductivities on the order of 2 x l0(exp -2) S/cm (120 C, 25% relative humidity). Our best results have been observed when films contain 60% PEO and 40% sulfonated melamine.

Tigelaar, Dean M.↗

NASA NTRS2007

Solidification Behavior of gamma'-Ni3Al Containing Alloys in the Ni-Al-O System

The chemical activities of Al and Ni in gamma(prime)-Ni3Al-containing systems were measured using the multi-cell Knudsen effusion-cell mass spectrometry technique (multi-cell KEMS), over the composition range 8 - 32 at.%Al and temperature range T = 1400 - 1750 K. From these measurements a better understanding of the equilibrium solidification behaviour of gamma(prime)-Ni3Al-containing alloys in the Ni-Al-O system was established. Specifically, these measurements revealed that (1) gamma(prime)-Ni3Al forms via the peritectiod reaction, gamma + Beta (+ A12O3) = gamma (prime) (+ Al2O3), at 1633 +/- 1 K, (2) the {gamma + Beta + Al2O3} phase field is stable over the temperature range 1633 through 1640 K, and (3) equilibrium solidification occurs by the eutectic reaction, L (+ Al2O3) = gamma + Beta (+ Al2O3), at 1640 +/- 1 K and a liquid composition of 24.8 +/- 0.2 at.%Al (at an unknown oxygen content). When projected onto the Ni-Al binary, this behaviour is inconsistent with the current Ni-Al phase diagram and a new diagram is proposed. This new Ni-Al phase diagram explains a number of unusual steady-state solidification structures reported previously and provides a much simpler reaction scheme in the vicinity of the gamma(prime)-Ni3Al phase field.

Copland, Evan↗

NASA NTRS2007

Effect of LEO Exposure on Aromatic Polymers Containing Phenylphosphine Oxide Groups

As part of the Materials on The International Space Station Experiment (MISSE), aromatic polymers containing phenylphosphine oxide groups were exposed to low Earth orbit (LEO) for approximately 4 years. All of the aromatic polymers containing phenylphosphine oxide groups survived the exposure despite the high fluence of atomic oxygen that completely eroded other polymer films such as Kapton and Mylar of comparable or greater thickness. The samples consisted of a colorless polyimide film and a poly(arylene ether benzimidazole) film and thread. The samples were characterized for changes in physical properties, thermal/optical properties (i.e. solar absorptivity and thermal emissivity), surface chemistry (X-ray photoelectron spectroscopy), and surface topography (atomic force microscopy). The data from the polymer samples on MISSE were compared to samples from the same batch of material stored under ambient conditions on Earth. In addition, comparisons were made between the MISSE samples and those subjected to shorter term space flight exposures. The results of these analyses will be presented.

Watson, K. A.↗

NASA NTRS1984

Microsphere coated substrate containing reactive aldehyde groups

A synthetic organic resin is coated with a continuous layer of contiguous, tangential, individual microspheres having a uniform diameter preferably between 100 Angstroms and 2000 Angstroms. The microspheres are an addition polymerized polymer of an unsaturated aldehyde containing 4 to 20 carbon atoms and are covalently bonded to the substrate by means of high energy radiation grafting. The microspheres contain reactive aldehyde groups and can form conjugates with proteins such as enzymes or other aldehyde reactive materials.

Rembaum, Alan↗

NASA NTRS1992

Aromatic polyimides containing a dimethylsilane-linked dianhydride

A high-temperature stable, optically transparent, low dielectric aromatic polyimide is prepared by chemically combining equimolar quantities of an aromatic dianhydride reactant and an aromatic diamine reactant, which are selected so that one reactant contains at least one Si(CH.sub.3).sub.2 group in its molecular structure, and the other reactant contains at least one --CH.sub.3 group in its molecular structure. The reactants are chemically combined in a solvent medium to form a solution of a high molecular weight polyamic acid, which is then converted to the corresponding polyimide.

St. Clair, Anne K.↗

NASA NTRS2008

Safety Review Panel (SRP) Special Topic Presentation on the Iodine Compatible Water Container (ICWC)

This viewgraph presentation reviews the safety requirements for the Iodine Compatible Water Container (ICWC). The topics include: 1) ICWC Team; 2) Purpose of presentation; 3) Background/Description of ICWC System; 4) Current status of ICWC Project; 5) HTV launch NCR Processing; 6) Tox 1 containment NCR processing; and 7) ISS on-orbit failure propagation and fault tolerance NCR processing.

Thomas, Evan A.↗

NASA NTRS2008

Effect of LEO Exposure on Aromatic Polymers Containing Phenylphosphine Oxide Groups

As part of the Materials on The International Space Station Experiment (MISSE), aromatic polymers containing phenylphosphine oxide groups were exposed to low Earth orbit for approx.4 years. All of the aromatic polymers containing phenylphosphine oxide groups survived the exposure despite the high fluence of atomic oxygen that completely eroded other polymer films such as Kapton(TradeMark) and Mylar(Trademark) of comparable or greater thickness. The samples were characterized for changes in physical properties, thermal/optical properties surface chemistry, and surface topography. The data from the polymer samples on MISSE were compared to samples from the same batch of material stored under ambient conditions on Earth. In addition, comparisons were made between the MISSE samples and those subjected to shorter term space flight exposures. The results of these analyses will be presented.

Lillehei, P. T.↗

NASA NTRS2008

Polymer composites containing nanotubes

The present invention relates to polymer composite materials containing carbon nanotubes, particularly to those containing singled-walled nanotubes. The invention provides a polymer composite comprising one or more base polymers, one or more functionalized m-phenylenevinylene-2,5-disubstituted-p-phenylenevinylene polymers and carbon nanotubes. The invention also relates to functionalized m-phenylenevinylene-2,5-disubstituted-p-phenylenevinylene polymers, particularly to m-phenylenevinylene-2,5-disubstituted-p-phenylenevinylene polymers having side chain functionalization, and more particularly to m-phenylenevinylene-2,5-disubstituted-p-phenylenevinylene polymers having olefin side chains and alkyl epoxy side chains. The invention further relates to methods of making polymer composites comprising carbon nanotubes.

Bley, Richard A.↗

NASA NTRS2008

Investigation, Analysis, and Testing of Self-contained Oxygen Generators

Self Contained Oxygen Generators (SCOGs) have widespread use in providing emergency breathing oxygen in a variety of environments including mines, submarines, spacecraft, and aircraft. These devices have definite advantages over storing of gaseous or liquid oxygen. The oxygen is not generated until a chemical briquette containing a chlorate or perchlorate oxidizer and a solid metallic fuel such as iron is ignited starting a thermal decomposition process allowing gaseous oxygen to be produced. These devices are typically very safe to store, easy to operate, and have primarily only a thermal hazard to the operator that can be controlled by barriers or furnaces. Tens of thousands of these devices are operated worldwide every year without major incident. This report examines the rare case of a SCOG whose behavior was both abnormal and lethal. This particular type of SCOG reviewed is nearly identical to a flight qualified version of SCOG slated for use on manned space vehicles. This Investigative Report is a compilation of a NASA effort in conjunction with other interested parties including military and aerospace to understand the causes of the particular SCOG accident and what preventative measures can be taken to ensure this incident is not repeated. This report details the incident and examines the root causes of the observed SCOG behavior from forensic evidence. A summary of chemical and numerical analysis is provided as a background to physical testing of identical SCOG devices. The results and findings of both small scale and full scale testing are documented on a test-by-test basis along with observations and summaries. Finally, conclusions are presented on the findings of this investigation, analysis, and testing along with suggestions on preventative measures for any entity interested in the safe use of these devices.

Keddy, Christopher P.↗

NASA NTRS2009

Novel Materials Containing Single-Wall Carbon Nanotubes Wrapped in Polymer Molecules

In this design, single-wall carbon nanotubes (SWNTs) have been coated in polymer molecules to create a new type of material that has low electrical conductivity, but still contains individual nanotubes, and small ropes of individual nanotubes, which are themselves good electrical conductors and serve as small conducting rods immersed in an electrically insulating matrix. The polymer is attached through weak chemical forces that are primarily non-covalent in nature, caused primarily through polarization rather than the sharing of valence electrons. Therefore, the electronic structure of the SWNT involved is substantially the same as that of free, individual (and small ropes of) SWNT. Their high conductivity makes the individual nanotubes extremely electrically polarizable, and materials containing these individual, highly polarizable molecules exhibit novel electrical properties including a high dielectric constant.

Smalley, Richard E.↗