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At least 811 records · Page 45
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Sintering and Interface Strain Tolerance of Plasma-Sprayed Thermal and Environmental Barrier Coatings

Ceramic thermal and environmental barrier coatings will be more aggressively designed to protect gas turbine engine hot section SiC/SiC Ceramic Matrix Composite (CMC) components in order to meet future engine higher fuel efficiency and lower emission goals. A coating system consisting of a zirconia-based oxide topcoat (thermal barrier) and a mullite/BSAS silicate inner coat (environmental barrier) is often considered a model system for the CMC applications. However, the coating sintering, and thermal expansion mismatch between the zirconia oxide layer and the silicate environmental barrier/CMC substrate will be of major concern at high temperature and under thermal cycling conditions. In this study, the sintering behavior of plasma-sprayed freestanding zirconia-yttria-based thermal barrier coatings and mullite (and/or barium-strontium-aluminosilicate, i.e., BSAS) environmental barrier coatings was determined using a dilatometer in the temperature range of 1200-1500 C. The effects of test temperature on the coating sintering kinetics were systematically investigated. The plasma-sprayed zirconia-8wt.%yttria and mullite (BSAS) two-layer composite coating systems were also prepared to quantitatively evaluate the interface strain tolerance of the coating system under thermal cycling conditions based on the dilatomentry. The cyclic response of the coating strain tolerance behavior and interface degradation as a function of cycle number will also be discussed.

Zhu, Dongming↗
NASA NTRS2015

Systems and Methods for Providing Insulation

Systems and methods provide a multi-layer insulation (MLI) that includes a plurality of sealed metalized volumes in a stacked arrangement, wherein the plurality of sealed metalized volumes encapsulate a gas therein, with the gas having one of a thermal insulating property, an acoustic insulating property, or a combination insulating property thereof. The MLI also includes at least one spacer between adjacent sealed metalized volumes of the plurality of sealed metalized volumes and a protective cover surrounding the plurality of sealed metalized volumes.

Golden, Johnny L.↗
NASA NTRS1993

Thermal Protection System design studies for lunar crew module

The results of a study to predict aeroheating and Thermal Protection System (TPS) requirements for manned entry vehicles returning to Earth from the moon are presented. The effects of vehicle size and lunar-return strategies on the aerothermodynamic environment and TPS design were assessed. Study guidelines were based on an Apollo Command Module (CM) configuration and lunar return strategies included direct entry and aerocapture followed by Low Earth Orbit entry (LEO). Convective heating was obtained by the boundary layer integral matrix procedure (BLIMP) code, and radiative heating was computed with the QRAD program. The AESOP-STAB code and the AESOP-THERM code were used for TPS analysis for ablating materials and nonablating materials respectively. Results indicated that there was an optimum size for minimum heating and that direct entry had higher heating rates than aerocapture. Aerocapture resulted in higher heat loads and TPS weight. The TPS weight factor was 6-8 percent for all lunar return strategies, with the TPS weight being about 50 percent less than that of the original Apollo CM vehicle.

Williams, S. D.↗
NASA NTRS1947

A Method for Calculating the Heat Required for Windshield Thermal Ice Prevention Based on Extensive Flight Tests in Natural Icing Conditions

An equation is presented for calculating the heat flow required from the surface of an internally heated windshield in order to prevent the formation of ice accretions during flight in specified icing conditions. To ascertain the validity of the equation, comparison is made between calculated values of the heat required and measured values obtained for test windshields in actual flights in icing conditions. The test windshields were internally heated and provided data applicable to two common types of windshield configurations; namely the V-type and the type installed flush with the fuselage contours. These windshields were installed on a twin-engine cargo airplane and the icing flights were conducted over a large area of the United States during the winters of 1945-46 and 1946-47. In addition to the internally heated windshield investigation, some test data were obtained for a windshield ice-prevention system in which heated air was discharged into the windshield boundary layer. The general conclusions resulting from this investigation are as follows: 1) The amount of heat required for the prevention of ice accretions on both flush- and V-type windshields during flight in specified icing conditions can be calculated with a degree of accuracy suitable for design purposes. 2) A heat flow of 2000 to 2500 Btu per hour per square foot is required for complete and continuous protection of a V-type windshield in fight at speeds up to 300 miles per hour in a moderate cumulus icing condition. For the same degree of protection and the same speed range, a value of 1000 Btu per hour per square foot suffices in a moderate stratus icing condition. 3) A heat supply of 1000 Btu per hour per square foot is adequate for a flush windshield located well aft of the fuselage stagnation region, at speeds up to 300 miles per hour, for flight in both stratus and moderate cumulus icing conditions. 4) The external air discharge system of windshield thermal ice prevention is thermally inefficient and requires a heat supply approximately 20 times that required for an internal system having the same performance.

ICE FORMATION↗
NASA NTRS2024

Optimization of Mission Enabling Broadband Lyman Ultraviolet Series to Infrared Aluminum Lithium Fluoride Reflectors

The Habitable Worlds Observatory (HWO) concept NASA flagship mission aims extend the ultraviolet (UV) observation range and sensitivity capabilities of the Hubble Space Telescope (HST) with respective goals of reaching photons down to 100 nm and containing an ultraviolet multi-object spectrograph with sensitivity improved 30-100 times. Adding the sensitivity capabilities near the Lyman series spectral range of ~100-121.6 nm reduces the reliance of redshift for key diagnostic ion lines such as O VI (103.2 nm), and heavily ionized gases of Ne VIII (77.5 nm) and MgX (62.5 nm). Clean and unoxidized aluminum (Al) reflectors provide optimal efficiency over a broadband down to the extreme ultraviolet (EUV) wavelength of ~83 nm. To prevent oxidation and maintain high spectral efficiency down to ~100 nm, the Al reflector is conventionally overcoated with a thin lithium fluoride (LiF) layer. We investigate the optimization of the deposition of the Al+LiF coating material composition to attain high spectral efficiency broadband reflectors down to 100 nm and enable the scientific goals of HWO. Lithium hexafluoroaluminate (Li3AlF6) is investigated as a different composition form of LiF to overcoat Al. The spectral efficiency and durability of the reflectors is evaluated. We will demonstrate the use of Li3AlF6 as an overcoat to protect aluminum yields ultra-high efficiency at the Hydrogen Lyman-alpha (HLyα, 121.6 nm) line with experimental reflectance values peaking up to 99%.

optical coatings↗
NASA NTRS2024

Optimization of Mission Enabling Broadband Lyman Ultraviolet Series to Infrared Aluminum Lithium Fluoride Reflectors

The Habitable Worlds Observatory (HWO) concept NASA flagship mission aims extend the ultraviolet (UV) observation range and sensitivity capabilities of the Hubble Space Telescope (HST) with respective goals of reaching photons down to 100 nm and containing an ultraviolet multi-object spectrograph with sensitivity improved 30-100 times. Adding the sensitivity capabilities near the Lyman series spectral range of ~100-121.6 nm reduces the reliance of redshift for key diagnostic ion lines such as O VI (103.2 nm), and heavily ionized gases of Ne VIII (77.5 nm) and MgX (62.5 nm). Clean and unoxidized aluminum (Al) reflectors provide optimal efficiency over a broadband down to the extreme ultraviolet (EUV) wavelength of ~83 nm. To prevent oxidation and maintain high spectral efficiency down to ~100 nm, the Al reflector is conventionally overcoated with a thin lithium fluoride (LiF) layer. We investigate the optimization of the deposition of the Al+LiF coating material composition to attain high spectral efficiency broadband reflectors down to 100 nm and enable the scientific goals of HWO. Lithium hexafluoroaluminate (Li3AlF6) is investigated as a different composition form of LiF to overcoat Al. The spectral efficiency and durability of the reflectors is evaluated. We will demonstrate the use of Li3AlF6 as an overcoat to protect aluminum yields ultra-high efficiency at the Hydrogen Lyman-alpha (HLyα, 121.6 nm) line with experimental reflectance values peaking up to 99%.

optical coatings↗
NASA NTRS2014

Radiative Heating for MSL Entry: Verification of Simulations from Ground Test to Flight Data

The heat shield of the Mars Science Laboratory (MSL) was equipped with thermocouplestacks to measure in-depth heating of the thermal protection system during atmosphericentry. The heat load derived from the thermocouples in the stagnation region was found tobe 33 lower than corresponding post-flight predictions of convective heating alone. It washypothesized that this difference could be attributed to radiation from the shock-heated gas,a mechanism not considered in post-flight analyses of flow fields. In order to test thehypothesis and quantify the contribution of shock-layer radiation to total surface heating,ground tests and simulations (both flow and radiation) were performed at several pointsalong the best-estimated entry trajectory of MSL. The present paper provides anassessment of the quality of the radiation model and its impact to stagnation point heating.Although the impact of radiative heating is shown to be significant, it only accounts for 43of the discrepancy. Additional factors behind the remaining discrepancy are discussed.

Aeroheating↗
NASA NTRS2018

Material Response Analysis of a Titan Entry Heatshield

Accurate calculation of thermal protection material response is critical to the vehicle design for missions to the Saturn moon Titan. In this study, Icarus, a three-dimensional, unstructured, finite-volume material response solver under active development at NASA Ames Research Center, is used to compute the in-depth material response of the Huygens spacecraft along its November 11 entry trajectory. The heatshield analyzed in this study consists of a five-layer stack-up of Phenolic Impregnated Carbon Ablator (PICA), aluminum honeycomb, adhesive, and face sheetmaterials. During planetary entry, the PICA outer layer is expected to undergo pyrolysis. A surface energy balance boundary condition that captures both time- and spatial-variance of surface properties during entry is used in the simulation.

material response↗
NASA NTRS1977

Auger spectroscopic examination of MgF2-coated Al mirrors before and after UV irradiation

Magnesium fluoride protected Al films were studied since these mirrors are commonly used in astronomical instruments whenever a highly reflecting optical surface is required in the wavelength region from 1100 A to 2000 A. Freshly prepared samples of evaporated Al + 250-A thick MgF2 on glass were analyzed by Auger electron spectroscopy in conjunction with surface erosion by Ar(+) ion bombardment before and after UV irradiation. The analysis showed that a very thin layer of surface contamination and not bulk photolysis in the MgF2 film was reponsible for the irradiation-induced reflectance loss. Postirradiation polishing with a mild calcium carbonate abrasive can restore a mirror's reflectance by removing the photolyzed surface film without disturbing the MgF2 layer.

Heaney, J. B.↗
NASA NTRS1978

Thermal insulation attaching means

An improved isolation system is provided for attaching ceramic tiles of insulating material to the surface of a structure to be protected against extreme temperatures of the nature expected to be encountered by the space shuttle orbiter. This system isolates the fragile ceramic tiles from thermally and mechanically induced vehicle structural strains. The insulating tiles are affixed to a felt isolation pad formed of closely arranged and randomly oriented fibers by means of a flexible adhesive and in turn the felt pad is affixed to the metallic vehicle structure by an additional layer of flexible adhesive.

Leger, L. J.↗
NASA NTRS2003

Atmospheric Boundary Layer Sensors for Application in a Wake Vortex Advisory System

Remote sensing of the atmospheric boundary layer has advanced in recent years with the development of commercial off-the-shelf (COTS) radar, sodar, and lidar wind profiling technology. Radio acoustic sounding systems for vertical temperature profiles of high temporal scales (when compared to routine balloon soundings- (radiosondes) have also become increasingly available as COTS capabilities. Aircraft observations during landing and departures are another source of available boundary layer data. This report provides an updated assessment of available sensors, their performance specifications and rough order of magnitude costs for a potential future aircraft Wake Vortex Avoidance System (WakeVAS). Future capabilities are also discussed. Vertical profiles of wind, temperature, and turbulence are anticipated to be needed at airports in any dynamic wake avoidance system. Temporal and spatial resolution are dependent on the selection of approach and departure corridors to be protected. Recommendations are made for potential configurations of near-term sensor technologies and for testing some of the sensor systems in order to validate performance in field environments with adequate groundtruth.

Zak, J. Allen↗
NASA NTRS2014

Griffith Saponite as an Analog for Clay Minerals at Yellowknife Bay in Gale Crater, Mars: A Marker for Low-temperature Hydrothermal Processes

The CheMin X-ray diffraction (XRD) instrument onboard the Mars Science Laboratory rover Curiosity in Gale Crater, Mars, discovered smectite in drill fines of the Sheepbed mudstone at Yellowknife Bay (YNB). The mudstone has a basaltic composition, and the XRD powder diffraction pattern shows smectite 02l diffraction bands peaking at 4.59 A for targets John Klein and Cumberland, consistent with tri-octahedral smectites (saponite). From thermal analysis, the saponite abundance is ~20 wt. %. Among terrestrial analogues we have studied, ferrian saponite from Griffith Park (Los Angeles, CA) gives the best match to the position of the 02l diffraction band of YNB saponites. Here we describe iron-rich saponites from a terrestrial perspective, with a focus on Griffith saponite, and discuss their implications for the mineralogy of Sheepbed saponite and its formation pathways. Iron-rich saponite: Iron-rich saponite on the Earth is recognized as a low-temperature (<100 C), authigenic alteration product of basalt [e.g., 4-16]. In the discussion that follows, we reference the position of the 02l band because it is a measure of the unit cell 'b' dimension of the octahedral layer and thus the cations (including Fe redox state) in the octahedral layer. Ordinarily, the 06l band near 1.5 A is used to determine the 'b' dimension of smectite, but this band is not accessible with MSL CheMin instrument. For reference, a ferrosaponite (i.e., Fe2+ saponite) studied by [15] has a 02l spacing of 4.72 A and Fe3+/Fe = 0.27 [15]. Samples of terrestrial ferrosaponite, however, are reported to oxidize on the timescale of days when removed from their natural environment and not protected from oxidation. The Griffith saponite is Mg-rich ferrian saponite, and sample AMNH 89172 has an 02l spacing of 4.59 A (same as the Sheepbed saponites) and Fe3+/Fe = 0.64 [3]. This similarity suggests that Sheepbed saponites are ferrian (incompletely oxidized ferrosaponite). More oxidized Griffith saponites (Fe3+/Fe > 0.90) have somewhat smaller 02l d-spacings and also show Mossbauer evidence for an XRD amorphous Fe-bearing phase (e.g., ferrihydrite, hisingerite, superparamagnetic ferric oxides, etc.). The Griffith saponite occurs as vesicle fills, as replacements of olivine, and as replacements of mesostasis (basaltic glass). Similar occurrence modes are reported elsewhere. Hisingerite has been proposed by [13] as the alteration product of ferrian saponite whose precursor by oxidation was ferrosaponite.

Morris, R.V.↗
NASA NTRSDate not supplied

Error Sources and Mitigation Strategies for Thermocouples Integrated in Flexible Thermal Protection System Materials

• The flexible thermal protection system (FTPS) on NASA’s Low-Earth Orbit Flight Test of an Inflatable Decelerator (LOFTID) vehicle will be instrumented with thermocouples (TCs) to measure the in-depth thermal response during entry into Earth’s atmosphere. Accurate flight temperature measurements are critical for verifying vehicle performance and reducing thermal model uncertainties. • The TC leads are routed from the measurement location to the data acquisition system within the same FTPS layer that they are monitoring the temperature. This approach eliminates the need to put holes in the FTPS layers. However, the insulated TC leads are exposed to high temperatures and large thermal gradients. • The baseline TCs were commercially available 30 AWG Type K TCs with a binder impregnated glass braid insulation. The glass braid is rated to a maximum continuous use temperature of 482°C. LOFTID’s heat pulse will be on the order of minutes and the maximum predicted temperature beneath the outermost FTPS layers is 1350°C.

R. A. Miller↗
NASA NTRS2000

Formation of Leading-Edge Pinholes in the Space Shuttle Wings Investigated

The space shuttle wing leading edge and nose cap are composed of a carbon/carbon composite that is protected by silicon carbide. The coefficient of thermal expansion mismatch leads to cracks in the silicon carbide. The outer coating of the silicon carbide is a sodium-silicate-based glass that becomes fluid at the shuttles high reentry temperatures and fills these cracks. Small pinholes roughly 0.1 mm in diameter have been observed on these materials after 12 or more flights. These pinholes have been investigated by researchers at the NASA Johnson Space Center, Rockwell International, the Boeing Company, Lockheed Martin Corporation, and the NASA Glenn Research Center at Lewis Field to determine the possible sources and the extent of damage. A typical pinhole is illustrated in the photomicrographs. These pinholes are found primarily on the wing leading edges and not on the nose cap, which is covered when the orbiter is on the launch pad. The pinholes are generally associated with a bead of zincrich glass. Examination of the orbiter and launch structure indicates that weathering paint on the launch structure leads to deposits of zinc-containing paint flakes on the wing leading edge. These may become embedded in the crevices of the wing leading edge and form the observed zinc-rich glass. Laboratory experiments indicate that zinc oxide reacts vigorously with the glass coating on the silicon carbide. Thus, it is likely that this is the reaction that leads to pinhole formation (Christensen, S.V.: Reinforced Carbon/Carbon Pin Hole Formation Through Zinc Oxide Attack. Rockwell International Internal Letter, RDW 96 057, May 1996). Cross-sectional examination of pinholes suggests that they are enlarged thermal expansion mismatch cracks. This is illustrated in the photomicrographs. A careful microstructural analysis indicates that the pinhole walls consist of layers of zinc-containing glass. Thus, pinholes are likely formed by zinc oxide particles lodging in crevices and forming a corrosive zinc-rich glass that enlarges existing cracks. Having established the likely source of the pinholes, we next needed to model the damage. Our concern was that if a pinhole went through the silicon carbide to the carbon/carbon substrate, oxygen would have a clear path to oxidize the carbon at high temperatures. This possibility was examined with studies in a laboratory furnace. An ultrasonic drill was used to make artificial pinholes in a sample of protected carbon/carbon. After exposure, the specimens were weighed and cross-sectioned to quantify the extent of oxidation below the pinhole. The results at higher temperatures showed good agreement with a simple diffusion-control model. This model is based on the two-step oxidation of carbon to carbon monoxide and carbon dioxide. The fluxes are illustrated in the final figure. The model indicates a strong dependence on pinhole diameter. For smaller diameters and short times, the oxidation of carbon is very limited.

Jacobson, Nathan S.↗
NASA NTRS1977

Cooling effectiveness of slot injection into a turbulent boundary layer

The cooling effectiveness of injection through multiple flush slots at an angle of 10 deg was studied experimentally in a wind tunnel. Air was injected from one to four slots into a turbulent Mach 6 boundary layer. The slot mass flow ratio is defined, and data which describe the dependence of the cooling effectiveness on the slot mass flow ratio are presented. Experimental values are indicated graphically for various cases of single and multiple slot injection, where the total mass injection (i.e., the sum of flow rates from each slot) is the same for each case. The results show that, for a given coolant mass flow rate, thermal protection over the maximum surface area can be accomplished best by injecting the coolant flow through multiple slots.

Howard, F. G.↗
NASA NTRS1979

Solar array strip and a method for forming the same

A flexible solar array strip is formed by providing printed circuitry between flexible layers of a nonconductive material, depositing solder pads on the printed circuitry, and storing the resulting substrate on a drum from which it is then withdrawn and advanced along a linear path. Solderless solar cells are serially transported into engagement with the pads and are infrared radiation to melt the solder and attach the cells to the circuitry. Excess flux is cleaned from the solar cells which are then encapsulated in a protective coating. The resulting array is then wound on a drum.

Mueller, R. L.↗
NASA NTRS1983

Analysis of aerothermal loads on spherical dome protuberances

Hypersonic flow over spherical dome protuberances was investigated to determine increased pressure and heating loads to the surface. The configuration was mathematically modeled in a time-dependent three-dimensional analysis of the conservation of mass, momentum (Navier-Stokes), and energy equations. A boundary mapping technique was used to obtain a rectangular parallelepiped computational domain, a MacCormack explicit time-split predictor-corrector finite difference algorithm was used to obtain solutions. Results show local pressures and heating rates for domes one-half, one, and two boundary layer thicknesses high were increased by factors on the order of 1.4, 2, and 6, respectively. Flow over the lower dome was everywhere attached while flow over the intermediate dome had small windward and leeside separations. The higher dome had an unsteady windward separation region and a large leeside separation region. Trailing vortices form on all domes with intensity increasing with dome height. Discussion of applying the results to a thermally bowed thermal protection system are presented.

Olsen, G. C.↗
NASA NTRS1971

Response of aerospace structures to reentry aerodynamic excitation

A bibliography on aerodynamic excitation and associated structural response is presented. Very little applicable data under actual reentry conditions was found, but many wind tunnel tests and some in-flight data were. Aerodynamic excitation and proposed space shuttle configurations and reentry trajectories were studied. Attached turbulent boundary layer, separated turbulent boundary layer, and base pressure fluctuations are the region of aerodynamic excitation most applicable to exterior panels of space shuttle-type vehicles; prediction techniques are presented for these environments. Methods for predicting the response of panel structures to acoustic excitation were investigated. A normal mode approach was developed for the low frequency response and a statistical energy approach was utilized for the high frequency response. A finite element model was made of a thermal protective system test panel. Computer programs were used to determine the natural frequencies and mode shapes of the panel and to calculate the response of the panel to a reverberant acoustic field. Power spectral densities of response displacement and acceleration are presented.

Carlin, D., Jr.↗