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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 1,495 records · Page 83
All sourcesNASA NTRSDOE OSTI
NASA NTRS2004

Mars Exploration Rovers landing dispersion analysis

Landing dispersion estimates for the Mars Exploration Rover missions were key elements in the site targeting process and in the evaluation of landing risk. This paper addresses the process and results of the landing dispersion analyses performed for both Spirit and Opportunity. The several contributors to landing dispersions (navigation and atmospheric uncertainties, spacecraft modeling, winds, and margins) are discussed, as are the analysis tools used. The JPL MarsLS program, a MATLAB-based landing dispersion visualization and statistical analysis tool, was used to calculate the probability of landing within hazardous areas. By convolving this with the probability of landing within flight system limits (in-spec landing) for each hazard area, a single overall measure of landing risk was calculated for each landing ellipse. In-spec probability contours were also generated, allowing a more synoptic view of site risks, illustrating the sensitivity to changes in landing location, and quantifying the possible consequences of anomalies such as incomplete maneuvers. Data and products required to support these analyses are described, including the landing footprints calculated by NASA Langley's POST program and the JPL AEPL program, cartographically registered base maps and hazard maps, and flight system estimates of in-spec landing probabilities for each hazard terrain type. Various factors encountered during operations, including evolving navigation estimates and changing atmospheric models, are discussed and final landing points are compared with approach estimates.

Desai, Prasun N.↗
NASA NTRS2017

The Epic Chronicle of Designing Cassini's Titan Flyby Altitudes

The selection and optimization of Titan flyby altitudes for NASA's Cassini mission at Saturn has traveled a long, fascinating, and often torturous sixteen-year path - starting in 2001, when pre-arrival trajectory design decisions had to be made, through April of 2017 when Cassini's last, and arguably most critical, low flyby takes place. The chronicle of designing and updating the Titan flyby altitudes have twists and turns enough to satisfy a full-length novel or feature film, including: critical design decision-making before arrival with multiple atmospheric models, high uncertainties, and limited data; early flybys that seemed to show trends that weren't there; use and misuse of statistical analysis; unexpected surprises with limited reaction time; navigation of a scientific, engineering, and management community with a wide array of inherent biases; and consideration of a variety of project risk postures in a high-scrutiny, high-impact, high-reward environment.

Bittner, Molly↗
NASA NTRSDate not supplied

Plume-Surface Interaction: Preliminary Observations from a Physics Focused Ground Test

Near surface operations conducted by spacecraft using rocket propulsion, such as during landing or the initial portion of ascent, may induce surface interactions that pose a risk to the spacecraft itself or nearby assets. NASA’s Space Technology Mission Directorate is conducting a multi-year project to mature the capability to predict plume-surface interactions (PSI) and reduce uncertainty through modeling, simulation, and ground testing. The Physics Focused Ground Test (PFGT), conducted in summer 2021, aimed to collect PSI data for plume, erosion, and ejecta physics to characterize PSI behaviors across a range of parameters relevant to the validation of computational modeling and with consideration to flight-relevant, though not flight-scale, environments. PFGT is a sub-scale, intrusive half-plane, inert-gas test conducted in a 15 foot-diameter vacuum chamber using a supersonic, heated, gaseous nitrogen plume. Tests were conducted with six regolith simulants, varying in complexity from spherical glass beads to BP-1 lunar soil simulant, and varied vacuum chamber ambient pressures to simulate Martian and lunar conditions. Nozzle height and mass flow rate were also varied to observe PSI behaviors and transitions of interest. Three high speed cameras captured crater formation and ejecta behavior during each test. An overview of this experiment is presented along with preliminary observations and analysis.

Wesley A Chambers↗
NASA NTRSDate not supplied

Understanding the Role of CFD, Including RANS, DES, LES and DNS, in Hypersonic Propulsion Design and Analysis

Computational fluid dynamics (CFD) has matured to the point where it is becoming ubiquitous in the design and analysis of aerospace vehicles and their propulsion systems. The current state-of-the-art of CFD in hypersonic propulsion design and analysis as well as a historical perspective of its development over the last 50 years is presented. The current state-of-the-art for the design of finite rate chemically reacting turbulent hypersonic flow is shown to currently be Reynolds averaged simulations (RAS) where the Reynolds averaged Navier-Stokes (RAS) equations are solved to obtain steady state solutions. An overview of the physical modeling techniques employed by RAS for the simulation of hypersonic chemically reacting flow are presented. However, scale resolving simulation techniques, such as detached eddy simulation (DES), large eddy simulations (LES), hybrid RAS/LES and direct numerical simulations (DNS), are becoming becoming powerful tools for point design analysis. One example of such a scale resolving technique, hybrid RAS/LES, will be briefly described as well as how it can be used to help address model form uncertainties in RAS.

Hypersonic↗
NASA NTRS2022

MODIS TEB Electronic Crosstalk Correction Update and Impact on L1B Product Uncertainty

The MODIS instruments onboard the Terra and Aqua satellites have been in operation for over22 and 20 years, respectively. The instruments’ calibration accuracy has been maintained, even with instrument degradation. Electronic crosstalk in the thermal emissive bands (TEB) is a known issue with an increasing impact on the calibration and product. The Terra MODIS photovoltaic (PV) longwave infrared (LWIR) bands crosstalk corrections have been applied in Collection 6.1 (C6.1). However, the electronic crosstalk contamination for some detectors in the mid-wave infrared (MWIR) bands and the Aqua PVLWIR bands affect the Level-1B (L1B) product’s measurement accuracy and image quality. In Collection 7 (C7), crosstalk corrections for select detectors in the Terra and Aqua MWIR and Aqua PV LWIR bands are applied. The entire mission crosstalk coefficients for the select detectors and bands are derived from scheduled lunar observations and populated in the form of look-up tables (LUTs). The Aqua PV-LWIR bands exhibit similar downward crosstalk trends as the Terra PV-LWIR bands, especially in recent years. The crosstalk coefficients and their trends provide a guideline for the correction application. Earth measurement analyses before and after the correction provide contamination and correction assessments. It has been shown that the product quality is enhanced with the crosstalk correction applied in C7. For C7, the crosstalk coefficient uncertainty is derived from the fit residuals between the measured values and a linear fit over a three-year sliding window. The uncertainty propagation is modeled and applied in the total uncertainty calculation intheL1B product. The TEB electronic crosstalk LUTs have been processed over the entire Terra and Aqua MODIS missions. This paper presents the C7 crosstalk correction, as well as its assessment and uncertainty propagation algorithm to the TEB uncertainty.

Tiejun Chang↗
NASA NTRS2023

Modelling the Greenland Ice Sheet's Committed Contribution to Sea Level During the 21st Century

Mass loss from the Greenland Ice Sheet can be partitioned between surface mass balance and discharge due to ice dynamics through its marine-terminating outlet glaciers. A perturbation to a glacier terminus (e.g., a calving event) results in both an instantaneous response in velocity and mass loss and a diffusive response due to the evolution of ice thickness over time. This diffusive response means the total impact of a retreat event can take decades to be fully realized. Here we model the committed response of the Greenland Ice Sheet by applying perturbations to the marine-terminating glacier termini that represent recent observed changes, and simulating the response over the 21st century, while holding the climate forcing constant. The sensitivity of the ice sheet response to model parameter uncertainty is explored within an ensemble framework, and Gravity Recovery and Climate Experiment data is used to constrain the results using a Bayesian calibration approach. We find that the Greenland Ice Sheet's committed contribution to 21st century sea level rise is at least 33.5 [17.5 52.4] mm (25th and 75th percentiles in brackets), with at least 6 mm being attributable directly to terminus retreat that occurred between 2007 and 2015. The spread in our projections is driven by uncertainty in the basal friction coefficient. Our results complement the ISMIP6 Greenland projections, which report the ice sheet response to future forcing, excluding the background response. In this way, we can obtain estimates of Greenland's total contribution to sea level rise in 2100.

Isabel J. Nias↗
NASA NTRS2023

Emission Factors for Crop Residue and Prescribed Fires in the Eastern US during FIREX-AQ

Agricultural and prescribed burning activities emit large amounts of trace gases and aerosols on regional to global scales. We present a compilation of emission factors (EFs) and emission ratios (ERs) from the eastern portion of the Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) campaign in 2019 in the United States, which sampled burning of crop residues and other prescribed fire fuels. FIREX-AQ provided comprehensive chemical characterization of 53 crop residue and 22 prescribed fires. Crop residues burned at different modified combustion efficiencies (MCE), with corn residue burning at higher MCE than other fuel types. Prescribed fires burned at lower MCE (<0.90) which is typical, while grasslands burned at lower MCE (0.90) than normally observed due to moist, green, growing season fuels. Most non-methane volatile organic compounds (NMVOCs) were significantly anticorrelated with MCE except for ethanol and NMVOCs that were measured with less certainty. We identified 23 species where crop residue fires differed by more than 50% from prescribed fires at the same MCE. Crop residue EFs were greater for species related to agricultural chemical use and fuel composition as well as oxygenated NMVOCs possibly due to the presence of metals such as potassium. Prescribed EFs were greater for monoterpenes (5×). FIREX-AQ crop residue average EFs generally agreed with the previous agricultural fire study in the US but had large disagreements with global compilations. FIREX-AQ observations show the importance of regionally-specific and fuel-specific EFs as first steps to reduce uncertainty in modeling the air quality impacts of fire emissions.

air quality↗
NASA NTRS2022

Modis TEB Electronic Crosstalk Correction Update and Impact on L1B Product Uncertainty

The MODIS instruments on board the Terra and Aqua satellites have been in operation for over 22 and 20 years, respectively. The instruments’ calibration accuracy has been maintained, even with instrument degradation. Electronic crosstalk in the thermal emissive bands (TEB) is a known issue with an increasing impact on the calibration and product. The Terra MODIS photovoltaic (PV) longwave infrared (LWIR) bands crosstalk corrections have been applied in Collection 6.1 (C6.1). However, the electronic crosstalk contamination for some detectors in the mid-wave infrared(MWIR) bands and the Aqua PVLWIR bands affect the Level-1B(L1B) product’s measurement accuracy and image quality. In Collection 7 (C7), crosstalk corrections for select detectors in the Terra and Aqua MWIR and Aqua PV LWIR bands are applied. The entire mission crosstalk coefficients for the select detectors and bands are derived from scheduled lunar observations and populated in the form of look-up tables (LUTs). The Aqua PV-LWIR bands exhibit similar downward crosstalk trends as the Terra PV-LWIR bands, especially in recent years. The crosstalk coefficients and their trends provide a guideline for the correction application. Earth measurement analyses before and after the correction provide contamination and correction assessments. It has been shown that the product quality is enhanced with the crosstalk correction applied in C7. For C7, the crosstalk coefficient uncertainty is derived from the fit residuals between the measured values and a linear fit over a three-year sliding window. The uncertainty propagation is modeled and applied in the total uncertainty calculation intheL1B product. The TEB electronic cross talk LUT shave been processed over the entire Terra and Aqua MODIS missions. This paper presents the C7 crosstalk correction, as well as its assessment and uncertainty propagation algorithm to the TEB uncertainty.

Tiejun Chang↗
NASA NTRSDate not supplied

Measurement of Secondary Electron Yield from Dielectric Materials

Secondary Electron Yield (SEY) is a material property that plays a fundamental role in material and spacecraft charging. SEY values for dielectric materials (insulators) are crucial inputs to models used to assess mission risk posed by high differential voltages and electrostatic discharge (ESD) on spacecraft. There are only two (non-NASA) facilities that attempt such measurements. The lack of NASA capability results in high cost and long, unpredictable schedules to obtain measurements. Future Artemis crewed lunar surface missions will involve the first use of many insulating materials for which SEY properties are poorly understood or absent entirely. Unconstrained SEY values in models increase uncertainty in charging/ESD risk assessment. The capability for reliable SEY determination will lead to improved charging and ESD risk assessments. We are developing a new capability, using pulsed ultralow (<femtoampere) incident electron beam intensity to eliminate sample charging, coupled with sensitive non-contact surface potential measurements, to measure secondary electron yield (SEY) from insulating materials. Present methods for SEY measurement on insulators suffer from highly inconsistent results due to sample charging from the incident electron beam during the measurement. In this first phase we are leveraging existing EM41 instrumentation, facilities, and expertise to perform proof-of-concept tests.

secondary electron emission↗
NASA NTRSDate not supplied

An Observation-Driven Framework for Modeling Post-Fire Hydrologic Response: Evaluation for Two Central California Case Studies

In a warming climate, wildfires are becoming increasingly common, especially in semi-arid environments. Wildfires can disrupt forest ecosystems and induce changes to the land surface. Collectively, these impacts can alter the hydrologic response of a catchment following a fire, resulting in increased potential for surface runoff, reduced evapotranspiration, and, ultimately, a higher risk for flash flooding and mass wasting. The timescale for post-fire recovery of hydrological processes to return to pre-fire conditions is not well established due to the lack of ground measurements. Accurate characterization of fire impacts on hydrologic response is also challenging to simulate, given the complex interplay of various processes. Here, we present a generalized framework to quantify wildfire impacts on runoff generation. We consider the vegetation and soil disturbances as the primary contributors to post-fire floods. Using an ensemble modeling structure to account for parameter uncertainty and consider model sensitivity, remotely sensed leaf area index (LAI) is assimilated into a land surface model (LSM) to simulate vegetation disturbance, and the maximum land surface saturation LSM parameter is decreased to parameterize the soil disturbance following observed fires. We evaluated the impacts of fire-induced changes to LAI and soil saturation on hydrologic states like runoff and evapotranspiration. Analysis of two events in central California shows that 1) the LAI assimilation has a greater impact on water balance; and 2) the soil scheme captures a range of outcomes, with substantial impacts on surface runoff for some ensemble members, which could affect flood potential.

Timothy M Lahmers↗