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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRS2018

Image Guider Subsystem Analysis for the GHAPS Project

The Gondola for High-Altitude Planetary Science (GHAPS) project is a balloon-borne astronomical observatory designed operate in the UV, Visible, and near-mid IR spectral region. The GHAPS Optical Telescope Assembly (OTA) is designed around a one meter aperture narrow field-of-view telescope with near-diffraction-limited performance. GHAPS will utilize Wallops Arc-Second Pointing System (WASP) for pointing the OTA with an accuracy of 1 arc second or better. WASP relies heavily on a self-contained star tracker assembly to determine the OTA line of sight. Preliminary structural analysis indicates that potential misalignments could be present between the OTA line of sight and the star tracker FOV center during the expected flight conditions that could compromise GHAPS pointing accuracy. In response the GHAPS project undertook a trade study to resolve the following issues: (1) estimate the worst case long-term (or bias) pointing misalignments for the GHAPS opto-mechanical configuration, (2) examine the need for additional hardware to correct pointing errors, and (3) determine the best hardware and software implementation to do so. Quantitative comparisons of performance and qualitative estimates of other factors such as mass, volume, power consumption, and cost are combined into an overall assessment of potential solutions. Results are discussed and a recommended implementation is given that is optimized to best achieve pointing performance goals, while minimizing impact to the design, cost, and resources of the GHAPS project.

Star Tracker↗
NASA NTRS1978

SAR/LANDSAT image registration study

The author has identified the following significant results. Temporal registration of synthetic aperture radar data with LANDSAT-MSS data is both feasible (from a technical standpoint) and useful (from an information-content viewpoint). The greatest difficulty in registering aircraft SAR data to corrected LANDSAT-MSS data is control-point location. The differences in SAR and MSS data impact the selection of features that will serve as a good control points. The SAR and MSS data are unsuitable for automatic computer correlation of digital control-point data. The gray-level data can not be compared by the computer because of the different response characteristics of the MSS and SAR images.

Murphrey, S. W.↗
NASA NTRS2016

eLISA Telescope In-field Pointing and Scattered Light Study

The orbital motion of the three spacecraft that make up the eLISA Observatory constellation causes long-arm line of sight variations of approximately ± one degree over the course of a year. The baseline solution is to package the telescope, the optical bench, and the gravitational reference sensor (GRS) into an optical assembly at each end of the measurement arm, and then to articulate the assembly. An optical phase reference is exchanged between the moving optical benches with a single mode optical fiber (“backlink” fiber). An alternative solution, referred to as in-field pointing, embeds a steering mirror into the optical design, fixing the optical benches and eliminating the backlink fiber, but requiring the additional complication of a two-stage optical design for the telescope. We examine the impact of an in-field pointing design on the scattered light performance.

Livas, J↗
NASA NTRS2012

The Distribution of Interplanetary Dust between 0.96 and 1.04 au as Inferred from Impacts on the STEREO Spacecraft Observed by the Heliospheric Imagers

The distribution of dust in the ecliptic plane between 0.96 and 1.04 au has been inferred from impacts on the two Solar Terrestrial Relations Observatory (STEREO) spacecraft through observation of secondary particle trails and unexpected off-points in the heliospheric imager (HI) cameras. This study made use of analysis carried out by members of a distributed webbased citizen science project Solar Stormwatch. A comparison between observations of the brightest particle trails and a survey of fainter trails shows consistent distributions. While there is no obvious correlation between this distribution and the occurrence of individual meteor streams at Earth, there are some broad longitudinal features in these distributions that are also observed in sources of the sporadic meteor population. The different position of the HI instrument on the two STEREO spacecraft leads to each sampling different populations of dust particles. The asymmetry in the number of trails seen by each spacecraft and the fact that there are many more unexpected off-points in the HI-B than in HI-A indicates that the majority of impacts are coming from the apex direction. For impacts causing off-points in the HI-B camera, these dust particles are estimated to have masses in excess of 10 (exp−17) kg with radii exceeding 0.1 μm. For off-points observed in the HI-A images, which can only have been caused by particles travelling from the anti-apex direction, the distribution is consistent with that of secondary 'storm' trails observed by HI-B, providing evidence that these trails also result from impacts with primary particles from an anti-apex source. Investigating the mass distribution for the off-points of both HI-A and HI-B, it is apparent that the differential mass index of particles from the apex direction (causing off-points in HI-B) is consistently above 2. This indicates that the majority of the mass is within the smaller particles of this population. In contrast, the differential mass index of particles from the anti-apex direction (causing off-points in HI-A) is consistently below 2, indicating that the majority of the mass is to be found in larger particles of this distribution.

Davis, C. J.↗
NASA NTRS1982

Lava flooding of ancient planetary crusts - Geometry, thickness, and volumes of flooded lunar impact basins

The present study is concerned with the determination of the geometry, thickness, volumes, and style of emplacement of lava extruded onto an ancient planetary crust, giving particular attention to crustal regions characterized by the topography of impact basins. Attempts to establish thicknesses and volumes are based on four approaches, related to crater morphometry, crater penetration, stratigraphy, and geophysical techniques. The considered technique is applied to two areas related to lunar impact areas. The Orientale basin is investigated, taking into account the style of flooding, the geometry of deposits and implications for loading of the lithosphere, and aspects of lava thickness and vertical mixing. An analysis of the Archimedes-Apennine Bench region is also conducted, giving attention to the number of data points, rim heights of fresh lunar craters, and the premare nature of impact crater data points.

Head, J. W.↗
NASA NTRSDate not supplied

Extending the Applicability of Thermal Protection System Ballistic Limit Equations Beyond the Testable Regime

All spacecraft use some sort of thermal insulation in their design, which is usually placed on the spacecraft’s exterior. As such, it is highly susceptible to high-speed impacts by meteoroids and orbital debris. These high-speed impacts can damage the insulation to a point where the protection it offers is below acceptable limits. It is, therefore, important to be able to characterize expected TPS damage levels stemming from such high-speed impacts. In a recent paper, we presented the results of a study that sought to characterize the high-speed impact damage that would be sustained by two thermal protection materials that have recently gained attention for possible use in interplanetary missions. As part of the analyses performed, ballistic limit equations for these materials were developed using recent high-speed impact test data, and then assessed by comparing their predictions against test data. In this paper, we extend the applicability of the ballistic limit equation for one of those thermal materials beyond the testable regime using the results of series of Smooth Particle Hydrodynamics Code (SPHC) impact simulations at velocities in excess of 10 km/s. When the predictions of the updated and expanded BLE were compared against the results of the SPHC runs, the predictions were seen to be consistent with the data: non-perforation data points were typically below the BLE curves, while perforation data points were typically above them.

Thermal Protection System↗
NASA NTRS1972

The 6300 A predawn enhancement - Excitation by photoelectrons from the magnetic conjugate point.

Incoherent scatter and tilting filter photometer data from Arecibo Observatory were combined to search for a contribution to the 6300 A predawn enhancement due to impact excitation by photoelectrons from the magnetic conjugate point. Prior to about 105 deg conjugate solar zenith angle, calculations of the 6300 A intensities due to dissociative recombination gave good agreement with the observed intensities. Then, with the arrival of conjugate photoelectrons (confirmed by plasma line enhancements), the observed intensities rose above the calculated, the difference increasing until a plateau was achieved at a conjugate solar zenith angle of about 95 deg. The difference or residual intensity is attributed to direct photoelectron impact excitation. Significant day-to-day variations in the onset angle and intensity have a strong negative correlation with ionospheric electron density.

Wickwar, V. B.↗
NASA NTRS1988

Dynamic fracture toughness of ceramic composites

The dynamic fracture toughness vs crack velocity relationships of TiB2 particulate-reinforced SiC-matrix and SiC whisker-reinforced Al2O3-matrix composites were determined at both room temperature and 1200 C with impacted, single-edge notched three-point bend specimens. Rapid crack initiation and propagation were monitored by a laser interferometric-displacement gage system. A FEM model that transmitted the measured outside-impact load to the specimen within the furnace was used to characterize the entire loading system-specimen unit. Small differences were measured between the room temperature and 1200 C dynamic responses.

Yang, K. H.↗
NASA NTRS2002

Earth to Moon Transfers - Direct vs Via Libration Points (L1, L2)

Recommend Direct Remote Ocean Area impact disposal for caseswithout hazardous (e.g., radioactive) material on LTV kickstage Controlled Earth contact. Relatively small disposal AV. Avoids close encounter with Moon. Trajectories can be very sensitive to initial conditions (at disposalmaneuver).V to correct for errors is small. Recommend Heliocentric Orbit disposal for cases with hazardousmaterial on LTV kickstage. No Earth or Lunar disposal issues (e.g.. impact location, debris footprint,litter). Relatively low disposal AV cost. Further study required to determine possibility of re-contact with Earth.

Condon, Gerald L.↗
NASA NTRS1993

Impact penetration experiments in teflon targets of variable thickness

Approximately 20.4 sq m of Teflon thermal blankets on the nonspinning Long Duration Exposure Facility (LDEF) were exposed to the orbital debris and micrometeoroid environment in low-Earth orbit (LEO) for approximately 5.7 years. Each blanket consisted of an outer layer (approximately 125 micron thick) of FEP Teflon that was backed by a vapor-deposited metal mirror (Inconel; less than 1 micron thick). The inner surface consisted of organic binders and Chemglaze thermal protective paint (approximately 50 micron thick) resulting in a somewhat variable, total blanket thickness of approximately 180 to 200 microns. There was at least one of these blankets, each exposing approximately 1.2 sq m of surface area, on nine of LDEF's 12 principal pointing directions, the exceptions being Rows 3, 9, and 12. As a consequence, these blankets represent a significant opportunity for micrometeoroid and debris studies, in general, and specifically they provide an opportunity to address those issues that require information about pointing direction (i.e., spatial density of impact events as a function of instrument orientation). During deintegration of the LDEF spacecraft at KSC, all penetration holes greater than or equal to 300 micron in diameter were documented and were recently synthesized in terms of spatial density as a function of LDEF viewing direction by. The present report describes ongoing cratering and penetration experiments in pure Teflon targets, which are intended to establish the relationships between crater or penetration-hole diameters and the associated projectile dimensions at laboratory velocities (i.e., 6 km/s). The ultimate objective of these efforts is to extract reliable mass-frequencies and associated fluxes of hypervelocity particles in LEO.

Hoerz, F.↗
NASA NTRS2022

Fatigue, Schedules, Sleep, and Sleepiness in U.S. Commercial Pilots During COVID-19

Introduction: COVID-19 has had a significant impact on the aviation industry. While reduced flying capacity may intuitively translate to reduced fatigue risk by way of fewer flights and duty hours, the actual impact of the pandemic on pilot fatigue is unknown. Methods: We surveyed US commercial airline pilots in late 2020 (n = 669) and early 2021 (n = 156) to assess the impact of COVID-19 on schedules and fatigue during the pandemic. Results: Overall, pilots reported reduced flight and duty hours compared to pre-pandemic. Average sleep on workdays was slightly shorter in late 2020 (6.88 h) and recovered to pre-pandemic levels in early 2021 (6.95 h). Similarly, the frequency of sleepiness on days off and in-flight increased in late 2020, with 54% of pilots reporting an increase in in-flight sleepiness, then returned to pre-pandemic levels in early 2021. The use of in-flight sleepiness countermeasures remained the same across assessed time points. Pilots highlighted several factors which impacted their sleep and job performance, including limited access to nutritional food during duty days and layovers, reduced access to exercise facilities during layovers, increased stress due to job insecurity and health concerns, increased distractions and workload, and changes to scheduling. Discussion: Despite a reduction in flights and duty days, COVID-19 led to increased sleepiness on days off and in-flight, potentially due to the negative impact of lack of access to essential needs and heightened stress on sleep. Operators need to monitor the change in these COVID-19 related risks as the industry returns to full service.

sleep↗
NASA NTRS2018

Radiative Heating of Large Meteoroids During Atmospheric Entry

A high-fidelity approach for simulating the aerothermodynamic environments of meteor entries was developed, which allows the commonly assumed heat transfer coefficient of 0.1 to be assessed. This model uses chemically reacting computational fluid dynamics (CFD), coupled with radiation transport and surface ablation. Coupled radiation accounts for the impact of radiation on the flowfield energy equations, while coupled ablation explicitly models the injection of ablation products within the flowfield and radiation simulations. For a meteoroid with a velocity of 20 km/s, coupled radiation is shown to reduce the stagnation point radiative heating by over 60%. The impact of coupled ablation (with coupled radiation) is shown to provide at least a 70% reduction in the radiative heating relative to cases with only coupled radiation. This large reduction is partially the result of the low ionization energies of meteoric ablation products relative to air species. The low ionization energies of ablation products, such as Mg and Ca, provide strong photoionization and atomic line absorption in regions of the spectrum that air species do not. MgO and CaO are also shown to provide significant absorption. Turbulence is shown to impact the distribution of ablation products through the shock-layer, which results in up to a 100% increase in the radiative heating downstream of the stagnation point. To create a database of heat transfer coefficients, the developed model was applied to a range of cases. This database considered velocities ranging from 14 to 20 km/s, altitudes ranging from 20 to 50 km, and nose radii ranging from 1 to 100 m. The heat transfer coefficients from these simulations are below 0.045 for the range of cases, for both laminar and turbulent, which is significantly lower than the canonical value of 0:1. When the new heat transfer model is applied to a Tunguska-like 15 Mt entry, the effect of the new model is to lower the height of burst by up to 2 km, depending on assumed entry angle. This, in turn, results in a significantly larger ground damage footprint than when the canonical heating assumption is used.

Christopher O Johnston↗
NASA NTRS2022

Implementation and Evaluation of Irrigation Techniques in the Community Land Model

Several previous studies have highlighted the irrigation-induced impacts on the global and regional water cycle, energy budget, and near-surface climate. While land models are widely used to address this question, the implementations of irrigation in these models vary in complexity. Here, we expand the representation of irrigation in Community Land Model to enable six different irrigation methods. We find that using a combination of irrigation methods, including default, sprinkler, flood and paddy techniques performs best as determined by evaluating the simulated irrigation water withdrawals against observations, and therefore select this combination as the new irrigation scheme. Then, the impact of the new irrigation scheme on surface fluxes is evaluated and detected using single-point simulations. Finally, the global and regional irrigation-induced impacts on surface energy and water fluxes are compared using both the original and the new irrigation scheme. The new irrigation scheme substantially reduces the bias and root-mean-square error of simulated irrigation water withdrawal in the USA and other countries, but considerably overestimates withdrawals in Central China. Results of single-point experiments show that different irrigation methods have different effects on surface fluxes, while the magnitudes are small. At the global scale, the new scheme enlarges the irrigation-induced impacts on water and energy variables relative to the original scheme, with varying magnitudes across regions. Overall, our results suggest that this newly developed scheme is a better tool for simulating irrigation-induced impacts on climate, and highlight the added value of incorporating human water management in Earth system models.

Community land models↗
NASA NTRS2010

A Point Spread Function for the EPOXI Mission

The Extrasolar Planet Observation Characterization and the Deep Impact Extended Investigation missions (EPOXI) are currently observing the transits of exoplanets, two comet nuclei at short range, and the Earth and Mars using the High Resolution Instrument (HRI) - a 0.3 m f/35 telescope on the Deep Impact probe. The HRI is in a permanently defocused state with the instrument pOint of focus about 0.6 cm before the focal plane due to the use of a reference flat mirror that took a power during ground thermal-vacuum testing. Consequently, the point spread function (PSF) covers approximately nine pixels FWHM and is characterized by a patch with three-fold symmetry due to the three-point support structures of the primary and secondary mirrors. The PSF is also strongly color dependent varying in shape and size with change in filtration and target color. While defocus is highly desirable for exoplanet transit observations to limit sensitivity to intra-pixel variation, it is suboptimal for observations of spatially resolved targets. Consequently, all images used in our analysis of such objects were deconvolved with an instrument PSF. The instrument PSF is also being used to optimize transit analysis. We discuss development and usage of an instrument PSF for these observations.

Barry, Richard K.↗
NASA NTRS1997

Generation Mechanisms UV and X-ray Emissions During SL9 Impact

The purpose of this grant was to study the ultraviolet and X-ray emissions associated with the impact of comet Shoemaker-Levy 9 with Jupiter. The University of Michigan task was primarily focused on theoretical calculations. The NAGW-4788 subtask was to be largely devoted to determining the constraints placed by the X-ray observations on the physical mechanisms responsible for the generation of the X-rays. Author summarized below the ROSAT observations and suggest a physical mechanism that can plausibly account for the observed emissions. It is hoped that the full set of activities can be completed at a later date. Further analysis of the ROSAT data acquired at the time of the impact was necessary to define the observational constraints on the magnetospheric-ionospheric processes involved in the excitation of the X-ray emissions associated with the fragment impacts. This analysis centered around improvements in the pointing accuracy and improvements in the timing information. Additional pointing information was made possible by the identification of the optical counterparts to the X-ray sources in the ROSAT field-of-view. Due to the large number of worldwide observers of the impacts, a serendipitous visible plate image from an observer in Venezuela provided a very accurate location of the present position of the X-ray source, virtually eliminating pointing errors in the data. Once refined, the pointing indicated that the two observed X-ray brightenings that were highly correlated in time with the K and P2 events were brightenings of the X-ray aurora (as identified in images prior to the impact).Appendix A "ROSAT observations of X-ray emissions from Jupiter during the impact of comet Shoemaker-Levy 9' also included.

Waite, J. Hunter, Jr.↗
NASA NTRS1972

Aiming strategies for quarantined multiplanet missions

An important flight path constraint for current and future interplanetary missions arises from planetary quarantine restrictions. Each planet is assigned a maximum allowable probability of contamination which must not be violated. A portion of this probability is suballocated among the trajectory correction maneuvers. The remaining portion is allocated to the small ejecta/efflux sources released from the spacecraft that could possibly reach the planetary atmsophere and surface. For each maneuver, the suballocation is translated into an allowable probability of planetary impact. At the time of making a maneuver, the allowable probability of impact may dictate biasing the aim point. This study describes the technique of determining preferred biased aim points, given the suballocated probability of contamination for each maneuver.

Dwivedi, N. P.↗
NASA NTRS1990

An examination of impact damage in glass-phenolic and aluminum honeycomb core composite panels

An examination of low velocity impact damage to glass-phenolic and aluminum core honeycomb sandwich panels with carbon-epoxy facesheets is presented. An instrumented drop weight impact test apparatus was utilized to inflict damage at energy ranges between 0.7 and 4.2 joules. Specimens were checked for extent of damage by cross sectional examination. The effect of core damage was assessed by subjecting impact-damaged beams to four-point bend tests. Skin-only specimens (facings not bonded to honeycomb) were also tested for comparison purposes. Results show that core buckling is the first damage mode, followed by delaminations in the facings, matrix cracking, and finally fiber breakage. The aluminum honeycomb panels exhibited a larger core damage zone and more facing delaminations than the glass-phenolic core, but could withstand more shear stress when damaged than the glass-phenolic core specimens.

Nettles, A. T.↗
NASA NTRS1990

Effects of off-axis radiation on reflective concentrating systems for space power

Off-axis incident radiation, resulting from misalignment of a concentrator relative to incident solar flux, can potentially result in high flux concentrations at positions other than the design focal point. It is suggested that the impact of these concentrations should be considered when choosing materials and thermal control strategies for structures adjacent to the concentrator. A numerical (ray tracing) analysis of the effects of off-axis radiation on the proposed solar concentrator for the Space Station Freedom is performed. The magnitude and position of the reflected flux peaks are identified for a matrix of off-axis angles and target distances. The principles of geometric optics are presented to illustrate that the results of the numerical study are justified, and these results are explained in terms of these basic optical principles. A method that allows prediction of the reflected flux field for a generalized parabolic reflective concentrating system is presented.

Campbell, J. S.↗