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Overcoming Dimensionality Barriers in Satellite Data to Elucidate SPECTRAL-SPATIAL-TEMPORAL Trends in the Ocean
Get PDFThe weighted harmonic mean of spectral wavelengths can be used as an index of optical water types that share similar spectral signatures.This technique can be translated to relate spectral shape between sensors of varying spectral resolution.The output along a continuum of color values enables spatio-temporal analysis of subtle spectral shifts.Directional trends in absorption and backscatter data lend a hidden context to changes in water color. Conceptualization of multiple data dimensions is imperative as passive/active sensors grow increasingly sophisticated in nature
Durability of YSZ Coated Ti2AlC in 1300 C Mach 0.3 Burner Rig Tests
Get PDFA thermal barrier coating system survived burner rig testing at 1300 C for 500 h. A 160 m thick yttria stabilized zirconia (YSZ) coating was applied to a Ti2AlC MAX phase bar sample by plasma spray physical vapor deposition (PS-PVD) and tested face-on in an atmospheric Mach 0.3 jet fuel burner, using 5-h thermal cycles. No thermal barrier coating (TBC) spallation or recession was observed, only a 2.4 mg/cm2 mass gain. The modest weight gain precluded severe volatility losses under high velocity burner conditions. The coating surface exhibited colonies of (111)flourite fiber-textured columns separated by craze patterns, with no visible moisture attack. The metastable tetragonal t' YSZ phase was obtained initially, transitioning to equilibrium teq and cubic YSZ, but with little detrimental monoclinic. The thickness of the alumina TGO was ~21 to 23 m under the heated YSZ face and ~13 to 15 m on the uncoated, cooler backside. The backside exhibited removal of initial transient TiO2 nodules and partial etching of the underlying Al2O3 scale by volatile hydroxides formed in high temperature, high velocity water vapor. Aerodynamic forces produced some bending of the cantilevered sample via creep. The test indicated exceptional stability of YSZ coatings on Ti2AlC under turbine conditions, with thermal expansion matching playing a key role. The purpose of this study was to demonstrate long term durability of YSZ/MAX phase system in aggressive high temperature burner rig testing.
MAX phases have been keenly studied because of their unique crystal structure and intriguing
properties (Refs. 1 and 2). Having Mn+1(Al,Si)(C,N)n general composition, they are defined as ceramics,
but possess unusual desirable attributes such as high conductivity, thermal shock resistance, easy
machinability, and deformation tolerance. The mechanical properties derive from weak M-(Al,Si)
bonding in the basal plane that leads to sliding and kinking in preference to catastrophic crack growth.
Like most ceramics they are phase stable at high temperatures, generally up to 1500 C. High temperature
oxidation resistance is excellent for alumina-forming Ti3AlC2, Ti2AlC, and Cr2AlC, as reviewed by
Tallman, et al. (Ref. 3). Compatibility with -Al2O3 scales is further enhanced in cyclic exposures by a
close matching of thermal expansion coefficients, (Ref. 4) i.e., (~9.3, 10.2, 11.3106/K for Al2O3,
Ti2AlC, and YSZ, to be discussed).
Turbine environments generally contain 10 percent water vapor in the combustion gases, therefore
moisture effects can be a concern for some materials (Ref. 5). Furnace tests of MAX phases in high
temperature steam generally showed little effect on Al2O3 scale growth (Ref. 6). However, high velocity
and high pressure gas can influence scale losses by the formation of volatile reaction products, such as
TiO(OH)2 and Al(OH)3 (Refs. 7 to 10). This phenomenon had been discussed for 1100 to 1300 C high
pressure burner rig tests of Ti2AlC (Ref. 11). A single cubic growth rate parameter kcubic was measurably
lower than comparable furnace TGA data, but it could be matched reasonably well if corrected for a slight
volatility term. In general, a two-parameter cubic-linear growth-volatility law was believed to apply.
Corresponding scale volatility loss rates, directly measured at 1300 C on a pre-oxidized sample, were
moderate (0.012 mg/cm2/h) and largely attributed to removal of the initial TiO2 transient scale.
A related CH4 burner study of high purity Cr2AlC MAX phase demonstrated 1200 C durability after
500 rapid (5 min. heat and 2 min. cool) thermal shock cycling (29 h hot time) (Ref. 12). Heating and
cooling rates were ~1000 and 500 C per minute, with a gas velocity of 5 m/s, producing a 75 C/mm
gradient. A 7 m Al2O3 surface scale and a 13 m Cr7C3 depletion zone formed with no signs of failure.
No evidence of scale volatility was evident, although weight change was not provided, the velocity was
moderate, and the total hot time was not extensive. The same high gradient BRT was used to produce
1400 C surface temperatures for a YSZ/Cr2AlC/IN738 system in the first study of MAX phases used as
bond coats for thermal barrier coatings (TBC) (Ref. 25). Here TBC failure was reported after 745 cycles,
with only a 1.5 m Al2O3 scale entrained within a porous, Cr7C3 bondcoat depletion phase.
YSZ thermal barrier coatings have been considered to be a compatible complement to Al-MAX
phases because of thermal expansion matching and extremely low volatility in water vapor. Initial studies
showed superior oxidative stability up to 1300 C, for long times (at least 500 h) for Ti2AlC substrates
and less (268 h) for Cr2AlC, while withstanding large alumina TGO scale thickness (~35 to 40 m)
(Refs. 13 and 14). By comparison, typical superalloy systems can only survive 1150 C maximum
interface temperatures for extended periods, with a maximum sustained TGO below 10 m (Ref. 15).
High temperature SiC based systems are known to form slow-growing SiO2 scales. But these are
subject to rate enhancement and volatile Si(OH)4 products in the presence of water vapor, as described
comprehensively by Opila, et al. (Refs. 5, 16 to 19). Net weight losses are generally observed in high
velocity, high pressure burner rig studies (e.g., 0.084 mg/cm2/h at 1300 C) (Ref. 20). Furthermore, the
loss rates have been shown from chemical physics to scale with v1/2 and pH2O
2 (Ref. 16). Low activity,
moisture-resistant environmental barrier coatings (EBC), such as rare earth silicates, are needed to
prevent substrate recession under turbine conditions (Refs. 21 to 23)
TESS Data Release Notes: Sector 20, DR27
Get PDFThis release note discusses the science data products produced by the Science Processing Operations Center at Ames Research Center from Sector 20 observations made with the TESS spacecraft and cameras as a means to document instrument performance and data characteristics
GN&C Sequencing for Orion Rendezvous, Proximity Operations, and Docking
Get PDFAs part of the Artemis program to return humans to the lunar surface, the National Aeronautics and Space Administration is planning to use the Orion Multi- Purpose Crew Vehicle to transport crew to a small orbital platform called Gate- way in cislunar space. To facilitate this activity, Orion is required to perform Rendezvous, Proximity Operations, and Docking (RPOD) with both the Gate- way and the launch vehicle upper stage. The Orion spacecraft uses sequencing in the form of Phases, Segments, Activities, and Modes (PSAM) to configure Guidance, Navigation, & Control (GN&C) software during each portion of the mission. Significant updates to Orion PSAM definitions are required for RPOD. This paper describes the process of defining these new sequencing elements, implementing them in prototype flight software, and testing them in an integrated simulation environment. First, requirements are specified to determine the nominal and off-nominal sequencing behavior necessary to complete the mission. These requirements also specify which software functions should be fully autonomous and which functions require manual interactions from crew or ground operators. Next, the RPOD concept of operations is defined with detailed events listed in a mission timeline. Third, a state machine diagram is developed to show all PSAM states, including all possible transitions between them. After this, the PSAM states and transitions are entered into a sequencing software emulator and parameter values and modes are defined for GN&C software elements. Finally, the PSAM architecture is tested within an integrated simulation environment by connecting it with prototypes of relevant GN&C flight software elements and with detailed vehicle models. After the sequencing design has been finalized and tested, it is implemented in flight software
Improvement of Shelf Life for Space Food Through a Hurdle Approach
Get PDFThe processed and prepackaged spaceflight food system is a critical human support system for manned space flights. As missions extend longer and farther from Earth over the next 20 years, strategies to stabilize the nutritional and sensory quality of food must be identified. For a mission to Mars, the space foods themselves must maintain quality for up to 5 years to align with cargo prepositioning scenarios. Optimizing the food system to achieve a 5-year shelf life mitigates the risk of an inadequate food system during extended missions. Because previous attempts to determine a singular pathway to a 5-year shelf life for food were unsuccessful, this investigation combines several approaches, based on science, technological advancement, and past empirical evidence, that will define the prepackaged food system for long duration missions. This study supports the Advanced Food Technology strategic planning process by identifying food processing, packaging, and storage technologies that will be required for exploration missions and the extent that they must be implemented to achieve a 5-year shelf life for the entire food system
Exploration Medical Capability (ExMC) Science and Research Overview and Update
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Impact of Satellite Microwave Radiance Data Assimilation on GEOS Atmospheric Analysis and Forecasts in Tropics
Get PDFThe NASA Global Modeling and Assimilation Office (GMAO) has developed a system to assimilate all-sky microwave radiance data in the Goddard Earth Observing System (GEOS). The system provides additional constraints on the analysis process near the storm regions and adjusts the geophysical parameters such as precipitation, cloud, moisture, surface pressure, and wind by combining information from microwave radiance measurements and model forecasts in an optimal manner. The system proved that assimilating the all-sky microwave radiance data improve the GEOS atmospheric analyses and forecasts. This all-sky data framework has been included in the GEOS Forward Processing (FP) system and currently assimilating all-sky GMI data in real-time for GEOS global analysis and forecast production at the GMAO. This presentation describes the methodologies to assimilate cloud- and precipitation-affected microwave radiances in GEOS data assimilation system based on hybrid four-dimensional ensemble-variational (4D-EnVar) configuration. In the current operational GEOS-FP system, the addition of all-sky GMI radiances has the largest impact in the Tropics. Specific humidity is significantly improved in the short term (0-72 hours) forecasts. Similar improvements are seen in the Tropical and lower tropospheric temperature and winds. More detailed results on all-sky microwave radiance data impact on GEOS analysis and forecasts are discussed in this presentation
Designing an Optimal Ensemble Strategy for GMAO S2S Forecast System
Get PDFGMAO Sub/Seasonal prediction system (S2S) is being readied for a major upgrade to GEOS-S2S Version 3. An important factor in successful extended range forecast is the definition of an ensemble For initialization of the ensemble we propose a combination of lagged and burst initial conditions. We plan to run a relatively large ensemble of 40 members for sub-seasonal forecast (up to 3 months), at which point we sub-sample the ensemble, and continue the forecast with 10 members (up to 12 months). Here we present the results of the extensive testing of various ways to generate the perturbations to the initial conditions and the validation of the stratified sampling strategy we chose.To generate perturbations for the burst ensemble members we used scaled differences of pairs of analysis states separated by 1-10 days, randomly chosen from a corresponding season. We considered perturbing separately only the atmospheric fields or only the ocean or both of the forecast initial conditions. Considering varying separation times between the analysis states, we were able to produce perturbations sampling various modes of variability. Focusing on the ENSO SST indices, we found that all types of perturbations are important for the ensemble spread.Our ensemble size for sub-seasonal forecasts was determined as to maximize the skill of predicting some of the leading modes of boreal winter atmospheric modes, NAO, PNA and AO. It is not feasible to run equally large ensemble for seasonal forecasts. Using a stratified sampling procedure we can identify the emerging directions of error growth. By comparing the stratified ensemble with randomly sampled ensemble of the same size, we were able to show that the former better estimates the mean of the original large ensemble
A Summary Of: Collecting Sleep, Circadian, Fatigue, and Performance Data in Complex Operational Environments
Get PDFSleep loss and circadian misalignment contribute to a meaningful proportion of operational accidents and incidents. Countermeasures and work scheduling designs aimed at mitigating fatigue are typically evaluated in controlled laboratory environments, but the effectiveness of translating such strategies to operational environments can be challenging to assess. This manuscript summarizes an approach for collecting sleep, circadian, fatigue, and performance data in a complex operational environment. We studied 44 airline pilots over 34 days while they flew a fixed schedule, which included a baseline data collection with 5 days of mid-morning flights, four early flights, four high-workload mid-day flights, and four late flights that landed after midnight. Each work block was separated by 3-4 days of rest. To assess sleep, participants wore a wrist-worn research-validated activity monitor continuously and completed daily sleep diaries. To assess the circadian phase, pilots were asked to collect all urine produced in four or eight hourly bins during the 24 h after each duty block for the assessment of 6-sulfatoxymelatonin (aMT6s), which is a biomarker of the circadian rhythm. To assess subjective fatigue and objective performance, participants were provided with a touchscreen device used to complete the Samn-Perelli Fatigue Scale and Psychomotor Vigilance Task (PVT) during and after each flight, and at wake-time, mid-day, and bedtime. Using these methods, it was found that sleep duration was reduced during early starts and late finishes relative to baseline. Circadian phase shifted according to duty schedule, but there was a wide range in the aMT6s peak between individuals on each schedule. PVT performance was worse on the early, high-workload, and late schedules relative to baseline. Overall, the combination of these methods was practical and effective for assessing the influence of sleep loss and circadian phase on fatigue and performance in a complex operational environment