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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.

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At least 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

Early Burn-In Parasitic Conduction in 500 °C Durable SiC JFET ICs

All prior reports of long-term 500 °C operation of SiC JFET-R ICs have noted the existence of an initial “burn-in” period of changes in measured electrical characteristics for the first few hundred hours oven-testing. This work reports measurements of “burn-in parasitic MOSFET conduction” that can substantially impact the performance of some circuits during initial heat-up of JFET ICs, but then subsequently disappears after a few hours of operation at 500 °C.

silicon carbide↗
NASA NTRSDate not supplied

Excessive Subsidence of the Southeast Atlantic Biomass Burning Aerosol Plume in the NASA Goddard Earth Observing System (GEOS) Model

Global models struggle to accurately represent the meteorological environment over the Southeast Atlantic Ocean, as evidenced by the poor representation of persistent marine stratocumulus decks off the west coast of southern Africa. This complex regime also experiences significant seasonal biomass burning aerosol plumes that are transported from southern Africa over the Atlantic Ocean, which gradually descend via large scale subsidence and interact radiatively and microphysically with the cloudy environment of the region. In comparisons to space borne lidar and aircraft observations we find that the NASA Goddard Earth Observing System (GEOS) model’s MERRA-2 aerosol and meteorology reanalysis shows that the aerosol plume descends too rapidly due to exaggerated large-scale downward vertical motion. This complicates the evaluation of aerosol properties utilizing aircraft observations collected throughout the ORACLES campaign as well as the model’s representation of the heating rate profiles due to the aerosol itself and its radiative interaction with the semi-permanent cloud deck typically located lower in altitude than the smoke. Two types of modeling experiments using GEOS will be presented to diagnose deficiencies in the model related to the excessive subsidence. Ensembles of free-running model simulations with and without radiatively active biomass burning aerosol will be used to quantify the impact of smoke on the atmospheric circulation. It will be demonstrated that heating within the aerosol layer results in self lofting through a reduction of the subsidence but did not alter the vertical placement or speed of the African Easterly jet. The amount of aerosol absorption required to eliminate the bias in the height of the aerosol plume through self-lofting will then be quantified. Finally, a second type of modeling experiment will be discussed in which the meteorology is constrained to observations. This will allow for biases in the height of the aerosol plume due to the general circulation model to be distinguished from biases that may be induced through the data assimilation process.

Allison Collow↗
NASA NTRSDate not supplied

Sampling of Space-Based Observations of XCO2 Associated With Biomass Burning Events

- The OCO-2 Level 3 assimilation product fills in gaps where OCO-2 does not have observations. - Although the Level 3 clearly shows the increased CO2 over the Amazon associated with the September 2017 biomass burning event, the total amount of CO2 may be underestimated because of a sampling bias. - The TCCON observations match fairly well with the OCO-2 observations and can be used to estimate the accuracy of the OCO observations and the temporal sampling bias. However, since it is a remotely sensed product, it may suffer the same sampling biases associated with biomass burning events as OCO-2. - Although aircraft data show that there is a significant variation in xCO2 with altitude, they suggest the OCO-2 fused products created by kriging may be better than the assimilated product at detecting large deviations from the average state on daily and regional scales.

Thomas J. Hearty, III↗
NASA NTRSDate not supplied

Sampling Biases of Space-Based Observations of XCO2 Associated With South American Biomass Burning Events During 2017-2020

- We examine time series of OCO-2 xCO 2 observations coincident with other remotely sensed and in-situ observations to better understand external sampling effects. - The OCO-2 Level 3 assimilation product fills in gaps where OCO-2 does not have observations. - Although the Level 3 clearly shows the increased CO 2 over the Amazon associated with the September 2017 biomass burning event, the total amount of CO 2 may be underestimated because of a sampling bias. - Since TCCON is also a remotely sensed product, it may suffer the same sampling biases associated with biomass burning events as OCO-2. - Aircraft data show that there is significant variation in xCO 2 with altitude. - The OCO-2 fused products created by kriging may be better than the assimilated product at detecting deviations from the average state.

OCO↗
NASA NTRSDate not supplied

Vehicle Modeling During the Burning of Thermally Thick Samples in the Saffire V Experiments

In order to design a safer spacecraft in terms of fire prevention, detection and cleanup, the transport of combustion products and heat must be predicted. Large-scale fire data was provided by the Saffire payload within Northrup Grumman’s Cygnus vehicle after a resupply mission to the ISS. Solid materials, including thick thermoplastic samples were ignited to study flame spread and the effect a fire has on a vehicle. Sensors that measured species and temperature were placed within Cygnus. A model using Pyrosim was developed to predict the thick fuel burn events from Saffire V by using sensor data from Cygnus. The heat transfer coefficient between the cabin air and cargo was previously calibrated using the cotton fuel burn event, and provided a good prediction of the temperature response within the vehicle during the two thick fuel experiments. The difference between the Saffire inlet CO 2 sensor, and the forward port standoff CO 2 sensor, which is the closest to the Saffire outlet, was used as an input into the model. This method provided an excellent prediction of the CO 2 response in the other parts of the Cygnus.

fire safety↗
NASA NTRS2022

Climate Drivers of Global Wildfire Burned Area

Wildfire is an integral part of the Earth system, but at the same time it can pose serious threats to human society and to certain types of terrestrial ecosystems. Meteorological conditions are a key driver of wildfire activity and extent, which led to the emergence of the use of fire danger indices that depend solely on weather conditions. The Canadian Fire Weather Index (FWI) is a widely used fire danger index of this kind. Here, we evaluate how well the FWI, its components, and the climate variables from which it is derived, correlate with observation-based burned area (BA) for a variety of world regions. We use a novel technique, according to which monthly BA are grouped by size for each Global Fire Emissions Database (GFED) pyrographic region. We find strong correlations of BA anomalies with the FWI anomalies, as well as with the underlying deviations from their climatologies for the four climate variables from which FWI is estimated, namely, temperature, relative humidity, precipitation, and wind. We quantify the relative sensitivity of the observed BA to each of the four climate variables, finding that this relationship strongly depends on the pyrographic region and land type. Our results indicate that the BA anomalies strongly correlate with FWI anomalies at a GFED region scale, compared to the strength of the correlation with individual climate variables. Additionally, among the individual climate variables that comprise the FWI, relative humidity and temperature are the most influential factors that affect the observed BA. Our results support the use of the composite fire danger index FWI, as well as its sub-indices, the Build-Up Index (BUI) and the Initial Spread Index (ISI), comparing to single climate variables, since they are found to correlate better with the observed forest or non-forest BA, for the most regions across the globe.

Wildfire↗
NASA NTRS2004

A Re-programmable Platform for Dynamic Burn-in Test of Xilinx Virtexll 3000 FPGA for Military and Aerospace Applications

Field Programmable Gate Arrays (FPGA) have played increasingly important roles in military and aerospace applications. Xilinx SRAM-based FPGAs have been extensively used in commercial applications. They have been used less frequently in space flight applications due to their susceptibility to single-event upsets. Reliability of these devices in space applications is a concern that has not been addressed. The objective of this project is to design a fully programmable hardware/software platform that allows (but is not limited to) comprehensive static/dynamic burn-in test of Virtex-II 3000 FPGAs, at speed test and SEU test. Conventional methods test very few discrete AC parameters (primarily switching) of a given integrated circuit. This approach will test any possible configuration of the FPGA and any associated performance parameters. It allows complete or partial re-programming of the FPGA and verification of the program by using read back followed by dynamic test. Designers have full control over which functional elements of the FPGA to stress. They can completely simulate all possible types of configurations/functions. Another benefit of this platform is that it allows collecting information on elevation of the junction temperature as a function of gate utilization, operating frequency and functionality. A software tool has been implemented to demonstrate the various features of the system. The software consists of three major parts: the parallel interface driver, main system procedure and a graphical user interface (GUI).

Field Programmable Gate Arrays (FPGA)↗
NASA NTRS2013

Integrated Active Fire Retrievals and Biomass Burning Emissions Using Complementary Near-Coincident Ground, Airborne and Spaceborne Sensor Data

Ground, airborne and spaceborne data were collected for a 450 ha prescribed fire implemented on 18 October 2011 at the Henry W. Coe State Park in California. The integration of various data elements allowed near coincident active fire retrievals to be estimated. The Autonomous Modular Sensor-Wildfire (AMS) airborne multispectral imaging system was used as a bridge between ground and spaceborne data sets providing high quality reference information to support satellite fire retrieval error analyses and fire emissions estimates. We found excellent agreement between peak fire radiant heat flux data (less than 1% error) derived from near-coincident ground radiometers and AMS. Both MODIS and GOES imager active fire products were negatively influenced by the presence of thick smoke, which was misclassified as cloud by their algorithms, leading to the omission of fire pixels beneath the smoke, and resulting in the underestimation of their retrieved fire radiative power (FRP) values for the burn plot, compared to the reference airborne data. Agreement between airborne and spaceborne FRP data improved significantly after correction for omission errors and atmospheric attenuation, resulting in as low as 5 difference between AquaMODIS and AMS. Use of in situ fuel and fire energy estimates in combination with a collection of AMS, MODIS, and GOES FRP retrievals provided a fuel consumption factor of 0.261 kg per MJ, total energy release of 14.5 x 10(exp 6) MJ, and total fuel consumption of 3.8 x 10(exp 6) kg. Fire emissions were calculated using two separate techniques, resulting in as low as 15 difference for various species

airborne scanner↗