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All sourcesNASA NTRSDOE OSTI
NASA NTRS2004

Vibration Isolation for Launch of a Space Station Orbital Replacement Unit

Delivery of Orbital Replacement Units (ORUs) to on-orbit destinations such a the International Space Station (ISS) and the Hubble Space Telescope is an important component of the space program. ORUs are integrated on orbit with space assets to maintain and upgrade functionality. For ORUs comprised of sensitive equipment, the dynamic launch environment drives design and testing requirements, and high frequency random vibrations are generally the cause for failure. Vibration isolation can mitigate the structure-borne vibration environment during launch, and hardware has been developed that can provide a reduced environment for current and future launch environments. Random vibration testing of one ORU to equivalent Space Shuttle launch levels revealed that its qualification and acceptance requirements were exceeded. An isolation system was designed to mitigate the structure-borne launch vibration environment. To protect this ORU, the random vibration levels at 50 Hz must be attenuated by a factor of two and those at higher frequencies even more. Design load factors for Shuttle launch are high, so a metallic load path is needed to maintain strength margins. Isolation system design was performed using a finite element model of the ORU on its carrier with representative disturbance inputs. Iterations on the modelled to an optimized design based on flight proven SoftRide MultiFlex isolators. Component testing has been performed on prototype isolators to validate analytical predictions.

Maly, Joseph R.↗
NASA NTRS1991

The SiH vibrational stretch as an indicator of the chemical state of interstellar grains

The infrared spectra of amorphous silicate grains and films formed in a variety of laboratory experiments have been measured. It is found that the frequency of the SiH fundamental stretch is extremely sensitive to the chemical environment of the grain in which the silicon is bound and varies from 2270/cm in oxidized grains to 2110/cm in a reducing environment. It is proposed that features previously observed in W33A could be due to -SiH groups in amorphous silica, partially reduced silica, silicon nitride or slightly oxidized silicon carbide. It is predicted that observations at 2270/cm will reveal a feature due to -SiH groups in highly oxidized interstelar and circumstellar grains. Such a feature might also appear in the spectra of comets.

Moore, Marla H.↗
NASA NTRS1999

Design Optimization of Stiffened Panels with Postbuckling Constraints

The funding provided by the grant is used to complete the final stages of the development of a geometrically nonlinear analysis and design capability for the static response of compressively loaded prismatic plate structures. The analysis is based on the nonlinear finite strip method and is applicable for structures, such as stiffened panels or box columns, that can be modeled as assemblages of finite length plate strips. In an effort to reduce the computational cost of the nonlinear finite strip method, thus making it suitable for use in the design optimization environment, reduced basis techniques as described in various references by Noor are used in conjunction with the finite strip method. In addition, an efficient scheme for tracing the nonlinear equilibrium paths through highly nonlinear response curves was implemented. The new scheme, which is referred to as the normal flow algorithm, is based on homotopy methods, and is capable of negotiating highly nonlinear limit point instabilities with a reduced computational cost compared to the popular Ricks/Wempner and Chrisfield algorithms.

Guerdal, Zafer↗
NASA NTRS1984

Occurrence of oxidized components in Qingzhen enstatite chondrite

It is shown that the most unequilibrated enstatite chondrite, Qingzhen, contains a population of enstatite grains which appear to have formed under more oxidizing nebular conditions than the bulk of the meteorite, which is highly reduced. These grains are black in transmitted light because of the presence of micron-sized inclusions of Ni-poor, Cr-rich metal, and occur either isolated within the matrix or in chondrule interiors. The textural occurrence of these grains argues against their having been introduced during collision of Qingzhen with an oxidized meteorite. Most likely, they originated in the same general nebular neighborhood of the reduced bulk Qingzhen material and were subsequently transported into the reducing environment either before or during the process of chondrule formation. The discovery of this once-oxidized material in Qingzhen posed significant constraints on existing models of formation of reduced matter in the solar system.

Rambaldi, E. R.↗
NASA NTRS2014

Sulfur-Bearing Phases Detected by Evolved Gas Analysis of the Rocknest Aeolian Deposit, Gale Crater, Mars

The Sample Analysis at Mars (SAM) instrument suite detected SO2, H2S, OCS, and CS2 from approx.450 to 800 C during evolved gas analysis (EGA) of materials from the Rocknest aeolian deposit in Gale Crater, Mars. This was the first detection of evolved sulfur species from a Martian surface sample during in situ EGA. SO2(approx. 3-22 micro-mol) is consistent with the thermal decomposition of Fe sulfates or Ca sulfites, or evolution/desorption from sulfur-bearing amorphous phases. Reactions between reduced sulfur phases such as sulfides and evolved O2 or H2O in the SAM oven are another candidate SO2 source. H2S (approx.41-109 nmol) is consistent with interactions of H2O, H2 and/or HCl with reduced sulfur phases and/or SO2 in the SAM oven. OCS (approx.1-5 nmol) and CS2(approx.0.2-1 nmol) are likely derived from reactions between carbon-bearing compounds and reduced sulfur. Sulfates and sulfites indicate some aqueous interactions, although not necessarily at the Rocknest site; Fe sulfates imply interaction with acid solutions whereas Ca sulfites can form from acidic to near-neutral solutions. Sulfides in the Rocknest materials suggest input from materials originally deposited in a reducing environment or from detrital sulfides from an igneous source. The presence of sulfides also suggests that the materials have not been extensively altered by oxidative aqueous weathering. The possibility of both reduced and oxidized sulfur compounds in the deposit indicates a nonequilibrium assemblage. Understanding the sulfur mineralogy in Rocknest materials, which exhibit chemical similarities to basaltic fines analyzed elsewhere on Mars, can provide insight in to the origin and alteration history of Martian surface materials.

evolved gas analysis↗
NASA NTRS2014

Sulfur-bearing Phases Detected by Evolved Gas Analysis of the Rocknest Aeolian Deposit, Gale Crater, Mars

The Sample Analysis at Mars (SAM) instrument suite detected SO2, H2S, OCS, and CS2 from ~450 to 800degC during evolved gas analysis (EGA) of materials from the Rocknest aeolian deposit in Gale Crater, Mars. This was the first detection of evolved sulfur species from a Martian surface sample during in situ EGA. SO2 (~3-22 μmol) is consistent with the thermal decomposition of Fe sulfates or Ca sulfites, or evolution/desorption from sulfur-bearing amorphous phases. Reactions between reduced sulfur phases such as sulfides and evolved O2 or H2O in the SAM oven are another candidate SO2 source. H2S (~41-109 nmol) is consistent with interactions of H2O, H2 and/or HCl with reduced sulfur phases and/or SO2 in the SAM oven. OCS (~1-5nmol) and CS2 (~0.2-1 nmol) are likely derived from reactions between carbon-bearing compounds and reduced sulfur. Sulfates and sulfites indicate some aqueous interactions, although not necessarily at the Rocknest site; Fe sulfates imply interaction with acid solutions whereas Ca sulfites can form from acidic to near-neutral solutions. Sulfides in the Rocknest materials suggest input from materials originally deposited in a reducing environment or from detrital sulfides from an igneous source. The presence of sulfides also suggests that the materials have not been extensively altered by oxidative aqueous weathering. The possibility of both reduced and oxidized sulfur compounds in the deposit indicates a nonequilibrium assemblage. Understanding the sulfur mineralogy in Rocknest materials, which exhibit chemical similarities to basaltic fines analyzed elsewhere on Mars, can provide insight in to the origin and alteration history of Martian surface materials.

Gale Crater↗
NASA NTRS2005

Tracing Oxygen Fugacity in Asteroids and Meteorites Through Olivine Composition

Olivine absorptions are known to dominate telescopic spectra of several asteroids. Among the meteorite collection, three groups (excluding Martian meteorites), the pallasites, brachinites, and R group chondrites are plausible analogs to olivine-rich asteroids in that they are dominated by olivine. These meteorite groups have distinct petrologic origins. The primitive achondrite brachinites (which include both depleted and undeleted subgroups) are products of relatively minor differentiation and evolved in oxidizing environments. R chondrites are also thought to have formed in high oxygen states, but are closely related to ordinary chondrites (yet with their own distinct compositions and oxygen isotopic signatures). In contrast, pallasites, widely thought to be mantle components from much more evolved bodies, formed in more reducing environments. Petrologic indicators that are identifiable in spectral data must be used in order to infer the petrologic history of asteroids from surveys of their actual population. As discussed below, olivine composition (e.g. Fa#) can provide key constraints in exploring the origin and significance of olivine dominated asteroids.

Sunshine, J. M.↗
NASA NTRS1991

Crystal-field-driven redox reactions: How common minerals split H2O and CO2 into reduced H2 and C plus oxygen

It is difficult to prove the presence of molecular H2 and reduced C in minerals containing dissolved H2 and CO2. A technique was developed which unambiguously shows that minerals grown in viciously reducing environments contain peroxy in their crystal structures. The peroxy represent interstitial oxygen atoms left behind when the solute H2O and/or CO2 split off H2 and C as a result of internal redox reactions, driven by the crystal field. The observation of peroxy affirms the presence of H2 and reduced C. It shows that the solid state is indeed an unusual reaction medium.

Freund, F.↗
NASA NTRS1986

Effects of atmosphere on the tribological properties of a chromium carbide based coating for use to 760 deg C

The effect of atmosphere on the tribological properties of a plasma-sprayed chromium carbide based self-lubricating coating is reported. The coating contains bonded chromium carbide as the wear resistant base stock to which the lubricants silver and barium fluoride/calcium fluoride eutectic are added. It has been denoted as NASA PS200. Potential applications for the PS200 coating are cylinder wall/piston ring couples for Stirling engines and foil bearing journal lubrication. Friction and wear studies were performed in helium, hydrogen, and moist air at temperatures from 25 to 760 C. In general, the atmosphere had a significant effect on both the friction and the wear of the coating and counterface material. Specimens tested in hydrogen, a reducing environment, exhibited the best tribological properties. Friction and wear increased in helium and air but are still within acceptable limits for intended applications. A variety of X-ray analyses was performed on the test specimens in an effort to explain the results. The following conclusions are made: (1) As the test atmosphere becomes less reducing, the coating experiences a higher concentration level of chromic oxide at the sliding interface which increases both the friction and wear. (2) Beneficial silver transfer from the parent coating to the counter-face material is less effective in air than in helium or hydrogen. (3) There may be a direct relationship between chromic oxide level present at the sliding interface and the friction coefficient.

Dellacorte, Chris↗
NASA NTRS1988

The effects of atmosphere on the tribological properties of a chromium carbide based coating for use to 760 C

The effect of atmosphere on the tribological properties of a plasma-sprayed chromium carbide based self-lubricating coating is reported. The coating contains bonded chromium carbide as the wear resistant base stock to which the lubricants silver and barium fluoride/calcium fluoride eutectic are added. It has been denoted as NASA PS200. Potential applications for the PS200 coating are cylinder wall/piston ring couples Stirling engines and foil bearing journal lubrication. Friction and wear studies were performed in helium, hydrogen, and moist air at temperatures from 25 to 760 C. In general, the atmosphere had a significant effect on both the friction and the wear of the coating and counterface material. Specimens tested in hydrogen, a reducing environment, exhibited the best tribological properties. Friction and wear increased in helium and air but are still within acceptable limits for intended applications. A variety of X-ray analyses was performed on the test specimens in an effort to explain the results. The following conclusions are made: (1) As the test atmosphere becomes less reducing, the coating experiences a higher concentration level of chromic oxide at the sliding interface which increases both the friction and wear. (2) Beneficial silver transfer from the parent coating to the counter-face material is less effective in air than in helium or hydrogen. (3) There may be a direct relationship between chromic oxide level present at the sliding interface and the friction coefficient.

Dellacorte, Christopher↗
NASA NTRS2016

Magnesium and Titanium Isotopic Compositions of an Unusual Hibonite-Perovskite Refractory Inclusion from Allende: It Is Fun

Introduction: Hibonite-rich refractory inclusions are among the first solids that formed in the solar nebula, and thus provide constraints on the earliest environment in the Solar System. An unusual hibonite-perovskite inclusion from Allende, SHAL, consists of a large (approximately 500 by 200 microns) single hibonite crystal and coexisting blocky perovskite (approximately 200 microns in size). The hibonite is characterized by chemical and oxygen isotopic compositions similar to those in the FUN (Fractionated and Unknown Nuclear anomalies) inclusion HAL. However, the rare earth element (REE) patterns measured at different spots of SHAL hibonite are highly variable, ranging from Group II-like (light REEs enriched relative to heavy REEs) to Group III-like (relatively flat with slight Eu depletions), but overall contrast largely with that of HAL, especially in the Ce and Yb abundances. This implies that SHAL hibonite formed and underwent distillation processes under more reducing conditions. Interestingly, the accompanying perovskite has uniform, unfractionated oxygen isotopic compositions (averaging delta (sup 17) O equals delta (sup 18) O equals −7 per mille) and REE abundances that are completely different from those of SHAL hibonite. This has been interpreted that perovskite and hibonite may not be co-genetic. Here we performed Al-Mg and Ti isotopic measurements of SHAL hibonite and perovskite to determine if the FUN characteristics are observed in these two isotope systems, and to further constrain the origin and evolution of SHAL. Results: Isotopic measurements of Al-Mg and Ti in SHAL were performed on the UCLA CAMECA ims-1290 ion microprobe by following the analytical protocols described in [1]. The Al-Mg and Ti data obtained in both terrestrial standards and SHAL hibonite and perovskite are shown below. Both SHAL hibonite and perovskite, despite very high (sup 27) Al to (sup 24) Mg ratios, are devoid of (sup 26) Mg excesses that can be attributed to the decay of (sup 26) Al. Delta (sup 25) Mg (mass-dependent fractionation) in hibonite is approximately −5 per mille per atomic mass unit relative to Madagascar hibonite, but is not well constrained for perovskite due to very large uncertainties owing to extremely low Mg contents. Similar to Mg isotopes, SHAL hibonite and perovskite show essentially the same Ti isotopic compositions, with anomalies in (sup 50) Ti of approximately 14 per mille, but the former shows greater Ti isotope fractionation than the latter (2.5 per mille per atomic mass unit versus 0 per mille). Discussion and Conclusions: The Al-Mg and Ti isotopic compositions of SHAL hibonite are consistent with those of HAL, suggesting that SHAL hibonite is a FUN inclusion and likely formed prior to homogenization of (sup 26) Al and Ti isotope variations in the solar nebula. However, the formation mechanisms for SHAL and HAL differ, given the differences in the REE patterns and degrees of oxygen mass-dependent fractionation. The Group-II to Group-III like REE patterns, the Yb depletions, and negative delta (sup 25) Mg observed in SHAL hibonite are all consistent with condensation of the hibonite precursor in a reducing environment.. The lack of large Ce depletions in SHAL hibonite implies that distillation processes that fractionated hibonite's oxygen isotopes must have taken place under a reducing condition, but the extent to which SHAL hibonite was distilled appears to be less than HAL because of the smaller degree of oxygen mass-dependent fractionation. The perovskite shares essentially the same Ti and Mg isotopic compositions as hibonite and probably formed in the same reservoir.. The ultrarefractory REE pattern seen in perovskite likely resulted from gas-solid fractionation which depleted HREEs in this reservoir. This process also explains why SHAL hibonite is generally depleted in HREEs relative to LREEs.

Liu, M.-C.↗
NASA NTRS2012

Paleo-Environment and C-14 Dating: The Key to the Depositional Age of the Tha Chang and Related Sand Pits, Northeastern Thailand

Tha Chang sand pits, Nakhon Ratchasima Province and many other sand pits in the area adjacent to the Mun River are characterized by their fluviatile environment in association with mass wasting deposits, along the paleo-river channel and the flood plain of the Mun River. Sediments of these deposits are characterized by clasts of various rock types especially the resistant ones with frequent big tree trunks, logs and wood fragments in different sizes and various stages of transformation from moldering stage to lignification and petrification. Widespread pyritization of the lower horizon suggests strongly reducing environment during burial. The Tha Chang deposits have been received much attention from geoscientists especially paleontologist communities, as they contain fragments of some distinct vertebrate species such as Stegadon sp., hominoid primate, rhinoceros Aceratherium and others. Based on the associated mammal fauna and hominoid fossils, the late Miocene ( 9 - 6 Ma) was given for the time of deposition of this sand and gravel unit. Some other reports believed that sediments and materials of these sand and gravel quarries (pits) were deposited by high-energy flood pulses contemporaneous with the tektites forming event during mid-Pleistocene at c. 0.8 Ma. Interpretation from Palynostratigraphical study suggested that the lower horizon of Tha Chang sand pit was deposited during Pliocene/Pleistocene period and the upper horizons are Pleistoncene/Holocene. It is crystal clear that all the fluviatile sediments including tektites and almost all fossil fragments being deposited in these sand pits were, likely a multiple times reworked materials. Only some old bamboo trees, some old crowling trees and fossils grasses observed on the old river bank are considered in situ. C-14 dating of 5 old wood specimens from Tha Chang Sand Pits, 15 old wood specimens from Chumpuang Sand Pits and one sample of old pottery from a Chumpuang Sand Pit were carried out in the NSF- Arizona AMS Laboratory. Although, there is no sharp boundary between the unconsolidated sedimentary horizons in the pits, C-14 ages obtained from the Tha Chang vary from 34,340 BP at the middle horizon (approx 10 m below ground zero) to >49,900 BP at the lower horizon with unknown basal formation (highly pyritized zone approx 20 - 25 m below ground zero). The ages for the Chumpuang vary from 41,700 BP, >45,900 BP and >49,900 BP from the upper most to the lower most of a broad horizon (approx 8 m to approx 12 m below ground zero). The C-14 age of the pottery collected from layer approximately 5 m below ground zero is 2,514 BP. The nature of fluviatile together with occasional mass wasting characteristics of all sand pits studies suggest the relatively faster depositional rate of the lower horizon which involved more flooding and mass wasting deposits than those of the upper horizons. The apparent of some mixing of the wood ages may indicate reworking and lag deposits nature of the area. The depositional rate of the upper most sand and soil horizon (5 m thick) is approximately 1 m per 500 years which mean both erosion and deposition had played a significant role during that time period. In term of the true age of the formation, we argue that since most of the materials deposited are reworked materials, all ages obtained from fossil fragments could not be the age of sand and gravel formation. Furthermore, the maximum age of all the tektite bearing horizons cannot be older than 0.8 Ma. The oldest C-14 age of 49,900 BP is interpreted as the minimum age of the Tha Chang and related sand pits formation when geomorphology of the area was a lot more hilly and much higher gradient than that of the present day.

Putthapiban, P.↗
NASA NTRS1994

NASA Lewis Research Center lean-, rich-burn materials test burner rig

The lean-, rich-burn materials test burner rig at NASA LeRC is used to evaluate the high temperature environmental durability of aerospace materials. The rig burns jet fuel and pressurized air, and sample materials can be subjected to both lean-burn and rich-burn environments. As part of NASA's Enabling Propulsion Materials (EPM) program, an existing rig was adapted to simulate the rich-burn quick-quench lean-burn (RQL) combustor concept which is being considered for the HSCT (high speed civil transport) aircraft. RQL materials requirements exceed that of current superalloys, thus ceramic matrix composites (CMC's) emerged as the leading candidate materials. The performance of these materials in the quasi reducing environment of the rich-burn section of the RQL is of fundamental importance to materials development. This rig was developed to conduct such studies, and its operation and capabilities are described.

Stearns, C. A.↗
NASA NTRS2008

Lunar Balance and Locomotion

Balance control and locomotor patterns were altered in Apollo crewmembers on the lunar surface, owing, presumably, to a combination of sensory-motor adaptation during transit and lunar surface operations, decreased environmental affordances associated with the reduced gravity, and restricted joint mobility as well as altered center-of-gravity caused by the EVA pressure suits. Dr. Paloski will discuss these factors, as well as the potential human and mission impacts of falls and malcoordination during planned lunar sortie and outpost missions. Learning objectives: What are the potential impacts of postural instabilities on the lunar surface? CME question: What factors affect balance control and gait stability on the moon? Answer: Sensory-motor adaptation to the lunar environment, reduced mechanical and visual affordances, and altered biomechanics caused by the EVA suit.

Paloski, William H.↗
NASA NTRS2004

Evidence for Differential Comminution/Aeolian Sorting and Chemical Weathering of Martian Soils Preserved in Mars Meteorite EET79001

Impact-melt glasses containing Martian atmospheric gases in Mars meteorite EET79001 are formed from Martian soil fines that had undergone meteoroid-comminution and aeolian sorting accompanied by chemical weathering near Mars surface. Using SiO2 and SO3 as proxy for silicates and salts respectively in Mars soils, we find that SiO2 and SO3 correlate negatively with FeO and MgO and positively with Al2O3 and CaO in these glasses, indicating that the mafic and felsic components are depleted and enriched relative to the bulk host (Lith A/B) respectively as in the case of Moon soils. Though the overall pattern of mineral fractionation is similar between the soil fines on Mars and Moon, the magnitudes of the enrichments/depletions differ between these sample-suites because of pervasive aeolian activity on Mars. In addition to this mechanical processing, the Martian soil fines, prior to impact-melting, have undergone acid-sulfate dissolution under oxidizing/reducing conditions. The S03 content in EET79001,507 (Lith B) glass is approx.18% compared to < 2% in EET79001, 506 (Lith A). SiO2 and SO3 negatively correlate with each other in ,507 glasses similar to Pathfinder soils. The positive correlation found between FeO and SO3 in ,507 glasses as well as Pathfinder rocks and soils is consistent with the deposition of ferric-hydroxysulfate on regolith grains in an oxidizing environment. As in the case of Pathfinder soils, the Al 2O3 vs SiO2 positive correlation and FeO VS S102 negative correlation observed in ,507 glasses indicate that SiO2 from the regolith is mobilized as soluble silicic acid at low pH. The large off-set in the end-member FeO abundance ( SO3=0) between Pathfinder soil-free rock and sulfur-free rock in ,507 glass precursors suggests that the soils comprising the ,507 glasses contain much larger proportion of fine-grained Martian soil fraction that registers strong mafic depletion relative to Lith B. This inference is strongly supported by the Al2O3 - SO3 negative correlation observed in both ,507 glasses and pathfinder soils. Furthermore, the flat MgO-SO3 correlation observed in the case of ,507 glasses shows that the solubilized MgSO4 is mobilized by the aqueous solutions leaving behind the rock-residue with approx.2-3% MgO. This value is similar to the approx.2% MgO found for the soil-free rock at the Pathfinder site. The EET79001 ,506 glasses, in contrast, show that Al2O3 and CaO positively correlate with SO3 indicating that Al is precipitated as amorphous hydroxysulfate at relatively high pH. The FeO - SO3 negative correlation observed in ,506 glasses yields an end-member FeO abundance of approx.21% for the sulfur-free rock, which is consistent with the 22% FeO deduced for the Viking soil-free rock. Further, the FeO and MgO negative correlation with S03 observed in ,506 glasses indicates that the divalent Fe and Mg released from ferromagnesian minerals by acid sulfate dissolution are mobilized away from the reaction sites as soluble sulfates under reducing environment. A similar negative correlation between FeO and SO3 and a positive correlation between Al2O3 and SO3 found in Viking soils suggest that they also had undergone acid-sulfate dissolution under relatively reducing conditions.

Rao, M. N.↗
NASA NTRS2006

Volume Ice Radiolysis in the Outer Solar System

The primary energy flux of charged particle components of the heliospheric and magnetospheric environments of the solar system is primarily carried by highly penetrating energetic particles. Although laboratory experiments on production of organics and oxidants typically only address effects on very thin surface layers, energy deposition occurs on surfaces of icy bodies of the outer solar system to meters in depth. Time scales for significant radiolytic deposition vary from thousands of years at millimeter depths on Europa to billions of years in the meters-deep regolith of Kuiper Belt Objects. Radioisotope decay (e.g., K-40) also contributes to volume radiolysis as the only energy source at much greater depths. Radiolytic oxygen is a potential resource for life within Europa and a partial source of oxygen for Saturn's magnetosphere and Titan's upper atmosphere. Interactions of very high energy cosmic rays with ices at Titan's surface may provide one of the few sources of oxidants in that highly reducing environment. The red colors of low-inclination classical Kuiper Belt Objects at 40-50 AU, and Centaur objects originating from this same population, may arise from volume radiolysis of deep ice layers below more refractory radiation crusts eroded away by surface sputtering and micrometeoroid impacts. A variety of techniques are potentially available to measure volume radiolysis products and have been proposed for study as part of the new Space Physics of Life initiative at NASA Goddard Space Flight Center. The technique of Electron Paramagnetic Resonance (EPR) has been used in medical studies to measure oxidant production in irradiated human tissue for cancer treatment. Other potential techniques include optical absorption spectroscopy and standard wet chemical analysis. These and other potential techniques are briefly reviewed for applicability to problems in solar system ice radiolysis and astrobiology.

Cooper, John F.↗
NASA NTRS1973

Magnetic studies on Apollo 15 and 16 lunar samples

The magnetic properties of lunar samples are almost exclusively due to rather pure metallic iron. The mare basalt contains about 0.06 wt.% Fe, the soils 0.5-0.6 wt.%, and the breccias 0.3-1.0 wt.%. Most of the additional iron in the soils and breccias is believed to be the result of reduction processes operating on the lunar surface. Whereas the total metallic iron content of the soils from all landing sites is rather constant, the Fe(0)/Fe(++) ratio and the average iron grain size increase with the age of the landing site, reflecting increasing maturity. The crystalline rocks studied from Apollo 16 have highly variable, but generally, very high metallic Fe content (up to 1.7 wt.% Fe). It is suggested that these rocks are either breccias or igneous samples which have been severely thermally metamorphosed in a highly reducing environment.

Pearce, G. W.↗
NASA NTRS1975

High temperature electrically conducting ceramic heating element and control system

Improvements were made in both electrode technology and ceramic conductor quality to increase significantly the lifetime and thermal cycling capability of electrically conducting ceramic heater elements. These elements were operated in vacuum, inert and reducing environments as well as oxidizing atmospheres adding to the versatility of the conducting ceramic as an ohmic heater. Using stabilized zirconia conducting ceramic heater elements, a furnace was fabricated and demonstrated to have excellent thermal response and cycling capability. The furnace was used to melt platinum-20% rhodium alloy (melting point 1904 C) with an isothermal ceramic heating element having a nominal working cavity size of 2.5 cm diameter by 10.0 cm long. The furnace was operated to 1940 C with the isothermal ceramic heating element. The same furnace structure was fitted with a pair of main heater elements to provide axial gradient temperature control over a working cavity length of 17.8 cm.

Halbach, C. R.↗