SEARCH · Search NASA
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.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Outgassing characteristics of nine epoxide adhesives, and thermal vacuum performance for adhesives tested
The procedures for determining the toxicity of products outgassed from spacecraft structures are discussed. The test equipment involved in the tests and the criteria for acceptability are described. The use of animals as the final step in determining toxicity of a spacecraft environment is explained.
The replacement of water (H2O) by deuterium oxide (D2O) and the exchange between atmospheric water and adsorbed or absorbed D2O were investigated for the polymeric materials Kapton and Mylar using thermal gravimetric analysis and infrared spectroscopy. Replacement of H2O by D2O is easily accomplished. However, exposure of D2O samples to the ambient atmosphere or gases containing H2O results in rapid proton and deuteron exchange between H2O vapor and adsorbed D2O. Replacement of H2O by D2O would not be a practical solution to alleviate spectral interferences that would result from water outgassing in spacecraft orbital environments. Maintaining the materials of interest in a dehydrated state is a more reasonable approach.
Data describing long-term materials performance under exposure to space environments has accumulated gradually over the past four decades. The authors present here selected results from several previous flight experiments and operational spacecraft, and a few examples from a current flight experiment. As examples of environmental effects on materials, analysis of Gortex samples from the Passive Optical Sample Assembly II (POSA II) experiment on the MIR-Shuttle docking module will be described. Results from a previous evaluation of radiation on silverized Teflon from over ten individual satellites will be summarized. Several examples of contamination effects on materials properties will be presented. These include outgassing of solar arrays onto nearby surfaces of the POSA I experiment and contamination of certain surfaces of the Long Duration Exposure Facility (LDEF). Results from experiments with silicone contamination on satellites in geosynchronous orbit will be compared with measurements on the Solar Maximum satellite and the LDEF. A number of techniques are being attempted to extend the range of exposure conditions present on selected experiments. Use of focusing concentrators on the Effect of Space Environments on Materials (ESEM), POSA, and Materials International Space Station Experiment (MISSE) will be described. A technique for obtaining time-resolved data from a passive materials experiment will be described. The status of an on-going materials flight experiment, MISSE, will be reported. Finally, the authors will draw some conclusions about the current state of knowledge relating to materials chosen for spacecraft applications. Understanding of degradation mechanisms, state of predictive models, and the need to strengthen model inputs will be discussed.
Irregular mare patches (IMPs) were previously proposed as sites of young lunar volcanism and/or endogenic activity [1-3], raising the possibility that volcanism on the Moon may not have ended approximately 1 Ga as determined from surface ages [4]. The wide-spread occurrence of more than 70 IMPs on the lunar nearside suggests a correlation with Th-rich PKT regions and a basaltic composition [1,2]. IMPs exhibit at least two types of deposit morphologies: (a) dome-like, steep-sided and smooth mounds and (b) low-relief ropy (LRR) to hummocky (LRH) materials (Fig. 1). Morphologic indicators such as steep (>40 deg) margin slopes across distances <10 m and crisp boundaries imply ages less than a few 100 Ma [e.g.,1-3]. The IMPs also have relatively few superposed craters >10 m in diameter, and young absolute model ages, which when combined with their superposition on young crater deposits like the continuous ejecta of Aristarchus crater, imply ages approximately 10 Ma to 100 Ma [1,2]. However, the mounds do not exhibit blocky crater morphologies, nor fracturing typical of young volcanic deposits, and the mound texture resembles that of mature regolith [e.g., 2,5], implying a much older age (approximately 3.5 Ga). These contrasting indicators have led to the proposal of widely varying formation mechanisms that range from ancient volcanism modified by recent tectonism [6] or outgassing [3,7], ancient volcanism of atypical materials [8], to Copernican-era volcanism [1,2].
In undertaking the design of a 2000-mm focal length camera for the Mariner Mark II series of spacecraft, JPL sought novel materials with the requisite dimensional and thermal stability, outgassing and corrosion resistance, low mass, high stiffness, and moderate cost. Metal-matrix composites and Al-Li alloys have, in addition to excellent mechanical properties and low density, a suitably low coefficient of thermal expansion, high specific stiffness, and good electrical conductivity. The greatest single obstacle to application of these materials to camera structure design is noted to have been the lack of information regarding long-term dimensional stability.
The outgassing properties of bare and magnetite-coated AISI 1020 low-carbon steel vacuum chambers were evaluated to establish material selection criteria for extreme high vacuum applications, namely, to explore the possibility of using these materials to build next-generation spin-polarized photoelectron guns. Water outgassing measurements using the throughput method revealed that the magnetite-coated chamber exhibited five times lower outgassing at room temperature prior to baking, but this advantage disappears after 80 °C baking. Hydrogen outgassing measurements demonstrated significant differences after intensive heat treatment: the bare low-carbon steel vacuum chamber achieved a specific outgassing rate of 9.6 × 10 −16 Torr L s −1 cm −2 after 400 °C/50 h bake plus additional heat treatment at lower temperatures, 25 times lower than the magnetite-coated low-carbon steel chamber. Residual gas analysis showed >99% hydrogen composition after heat treatment for both materials, with carbon species below detection limits for bare low-carbon steel versus 0.8% for magnetite-coated surfaces. These measurements indicate that properly conditioned bare low-carbon steel can achieve the <10 −12 Torr pressures required for next-generation spin-polarized photogun applications. In conclusion, the paper includes various analysis techniques intended to explain observed behaviors: isotherm analysis of pump-down plots, Arrhenius analysis of hydrogen outgassing rate data, and residual gas composition tracking.
Abstract This study describes computer simulations of carbonization and graphite formation, including the effects of hydrogen, nitrogen, oxygen, and sulfur. We introduce a novel technique to simulate carbonization, ‘Simulation of Thermal Emission of Atoms and Molecules (STEAM)’, designed to elucidate volatile outgassing and density variations in the intermediate material during carbonization. The investigation analyzes the functional groups that endure through high-temperature carbonization and examines the graphitization processes in carbon-rich materials containing non-carbon impurity elements. The physical, vibrational, and electronic attributes of impure amorphous graphite are analyzed, and the impact of nitrogen on electronic conduction is investigated.
Exposure of the volatile condensable material (VCM) from Silastic 140 RTV adhesive sealant to 147. 0-nm radiation, simulating the space radiation environment in synchronous earth orbits, induces absorption of visible light by the VCM. This results in an increase in the absorptance of coated optical elements, such as solar cell cover glasses and second-surface mirrors for thermal control. A contaminant thickness of 0.1 micron or more could result in a change in solar absorptance of the second-surface mirrors from 0.06 to approximately 0.16 in a period of about 1.5 years in space. Calculations indicated that the VCM thickness would have to be less than approximately 0.005 micron to keep the change in solar absorptance 0.01 for a 3-year mission.
The mechanical behavior of a filled elastomer was studied with emphasis on understanding the vacuum-material interactions occurring, and to develop analytical techniques for predicting the vacuum behavior. The test results indicate that two separate mechanisms are involved in the observed property changes: the first controls the time response to applied stress; the second determines the initial internal state of the materials as the result of stresses. It is concluded that the mechanical property changes are attributable to changes in the relaxation processes occurring in the material. These changes are brought about by outgassing of water. Recommendations for future investigations are included.
The effect of an ultrahigh vacuum and low water vapor pressure on the stress-strain relation in rocks was studied in order to understand geologic and tectonic processes of the moon. Terrestrial basaltic rocks carefully outgassed in high vacuum provided the sample material for the compression tests reported here. The tests were conducted either under 1 atm air saturated with moisture, or under high vacuum. Results of the stress-strain determinations indicated that the dry rocks could show as much as twice the strength of the wet rocks. The data may also provide a means of reconciling the high strength and high temperature exhibited by the lunar interior.
An animal exposure test system (AETS) was designed and fabricated for the purpose of collecting physiological and environmental (temperature) data from animal subjects exposed to combustion gases in large scale fire tests. The AETS consisted of an open wire mesh, two-compartment cage, one containing an exercise wheel for small rodents, and the other containing one rat instrumented externally for electrocardiogram (ECG) and respiration. Cage temperature is measured by a thermistor located in the upper portion of the rat compartment. Animal activity is monitored by the ECG and the records indicate an increase in EMG (electromyograph) noise super-imposed by the increased activity of the torso musculature. Examples of the recordings are presented and discussed as to their significance regarding toxicity of fire gases and specific events occurring during the test. The AETS was shown to be a useful tool in screening materials for the relative toxicity of their outgassing products during pyrolysis and combustion.
An inflatable structural system to deploy a space system such as a solar shield, an antenna or another similar instrument, requires a stiffening element after it is extended by the inflated gas pressure. The stiffening element has to be packaged in a folded configuration before the deployment. It must be relatively small, lightweight, non-damaging to the inflated system, and be able to become stiff in a short time. One stiffening method is to use a flexible material inserted in the deployable system, which, upon a temperature curing, can become stiff and is capable to support the entire structure. There are two conditions during the space operations when the inflated volume could be damaged: during the transonic region of the launch phase and when the curing of the rigidizing element occurs. In both cases, an excess of pressure within the volume containing the rigid element could burst the walls of the low-pressure gas inflated portion of the system. This paper investigates those two conditions and indicates the vents, which will prevent those damaging overpressures. Vent openings at the non-inflated volumes have been calculated for the conditions existing during the launch. Those vents allow the initially folded volume to exhaust the trapped atmospheric gas at approximately the same rate as the ambient pressure drops. That will prevent pressure gradients across the container walls which otherwise could be as high as 14.7 psi. The other condition occurring during the curing of the stiffening element has been investigated. This has required the testing of the element to obtain the gas generation during the curing and the transformation from a pliable material to a rigid one. The tested material is a composite graphite/epoxy weave. The outgassing of the uncured sample at 121C was carried with the Cahn Microbalance and with other outgassing facilities including the micro-CVCM ASTM E-595 facility. The tests provided the mass of gas evolved during the test. That data, including the chemical nature of the evolved gas, provided the data for the calculation of the pressure produced within the volume. The evaluation of the areas of the vents that would prevent excessive pressures and provide a rapid release of the gas away from contamination sensitive surfaces has been carried out. The pressure decay with time has been indicated.
An inflatable structural system to deploy a space system such as a solar shield, an antenna or another similar instrument requires a stiffening element after it is extended by the inflated gas pressure. The stiffening element has to be packaged in folded configuration before the deployment. It must be relatively small, lightweight, non-damaging to the inflated system and be able to become stiff in a short time. One stiffening method is to use a flexible material inserted in the deployable system, which, upon a temperature curing, can become stiff and is capable of supporting the entire structure. There are two conditions during the space operations when the inflated volume could be damaged: during the transonic region of the launch phase and when the curing of the rigidizing element occurs. In both cases, an excess of pressure within the volume containing the rigid element could burst the walls of the low-pressure gas inflated portion of the system. This paper investigates those two conditions and indicates the vents, which will prevent those damaging overpressures. Vent openings at the non-inflated volumes have been calculated for the conditions existing during the launch. Those vents allow the initially folded volume to exhaust the trapped atmospheric gas at approximately the same rate as the ambient pressure drops. That will prevent pressure gradients across the container walls which otherwise could be as high as 14.7 psi. The other condition occurring during the curing of the stiffening element has been investigated. This has required the testing of the element to obtain the gas generation during the curing and the transformation from a pliable material to a rigid on The tested material is a composite graphite/epoxy weave. The outgassing of the uncured sample at 121 deg Celcius was carried with the Cahn Microbalance and with other outgassing facilities including the micro-CVCM ASTM E-595 facility. The test provided the mass of gas evolved during the test. That data, including the chemical nature of the evolved gas, provided the data for the calculation of the pressure produced within the volume. The evaluation of the areas of the vents that would prevent excessive pressures and provide a rapid release of the gas away from contamination sensitive surfaces has be carried out. The pressure decay with time has been indicated.
It is shown that deposition of contamination films on satellite optics can be controlled by the following means: isolating critical optical surfaces from the rest of the spacecraft; avoiding or minimizing the use of nonmetallic material, particularly near or in line of sight of optical surfaces; avoiding materials with high vapor pressures; subjecting materials to vacuum baking prior to use, to drive off the volatile outgassing products; keeping the critical surfaces at temperatures above the ambient; avoiding elevated operational temperatures for nonmetallic materials; paying special attention to optics exposed to intense UV-, X-ray, or particular radiation; avoiding water-vapor sources; and directing RCS plumes away from critical surfaces. Methods of controlling particulate contaminants are also proposed.
To prevent the use of spacecraft material that would outgas objectionable or nauseating odors, an odor test was developed. This test provided a means whereby candidate spacecraft materials were subjected to a particular environment and the outgassed products were evaluated by an odor panel. This panel was comprised of individuals with acute olfactory senses. The test results of the odor panel provided design engineers with data regarding potential material-odor problems. The odor-test procedure, panel-member selection, and odor scoring methods are described and typical test results are presented.
As a coating made of highly porous zeolite materials, the Molecular Adsorber Coating (MAC) was developed to capture outgassed molecular contaminants, such as hydrocarbons and silicones. For spaceflight applications, the adsorptive capabilities of the coating can alleviate on-orbit outgassing concerns on or near sensitive surfaces and instruments within the spacecraft. Similarly, this sprayable paint technology has proven to be significantly beneficial for ground-based space applications, in particular, for vacuum chamber environments. This presentation describes the application of the MAC technology for the James Webb Space Telescope (JWST) at NASA Johnson Space Center (JSC). The coating was used as a mitigation tool to entrap outgassed contaminants, specifically silicone-based diffusion pump oil, from within JSCs cryogenic optical vacuum chamber test facility called Chamber A. This presentation summarizes the background, fabrication, installation, chemical analysis test results, and future plans for the MAC technology, which was effectively used to protect the JWST test equipment from vacuum chamber contamination. As a coating made of highly porous zeolite materials, the Molecular Adsorber Coating (MAC) was developed to capture outgassed molecular contaminants, such as hydrocarbons and silicones. For spaceflight applications, the adsorptive capabilities of the coating can alleviate on-orbit outgassing concerns on or near sensitive surfaces and instruments within the spacecraft. Similarly, this sprayable paint technology has proven to be significantly beneficial for ground-based space applications, in particular, for vacuum chamber environments. This presentation describes the application of the MAC technology for the James Webb Space Telescope (JWST) at NASA Johnson Space Center (JSC). The coating was used as a mitigation tool to entrap outgassed contaminants, specifically silicone-based diffusion pump oil, from within JSCs cryogenic optical vacuum chamber test facility called Chamber A. This presentation summarizes the background, fabrication, installation, chemical analysis test results, and future plans for the MAC technology, which was effectively used to protect the JWST test equipment from vacuum chamber contamination.
Spacecraft systems are baked-out under vacuum to remove occluded and adsorbed gases, solvents, water, plasticizer, and other materials acquired during their manufacture. Two bakeouts of solar panels were carried out. Quartz crystal microbalances installed in the vacuum chamber during the tests and held at 273 K (0 C) provided an ongoing measure of the panels' outgassing. From these data, the panels' material weight losses versus time were obtained. A comparison of the total weight loss expected during a relatively long bakeout with that accomplished during a reasonable period of time was used as a criteria for an acceptable duration of the bakeout in order to optimize cost effectiveness.