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At least 271 records · Page 15
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NASA NTRS2011

Investigating the Sources and Timing of Projectiles Striking the Lunar Surface

The lunar surface is exposed to bombardment by asteroids, comets, and debris from them. Surviving fragments of those projectiles in the lunar regolith provide a direct measure of the sources of exogenous material delivered to the Moon. Con-straining the temporal flux of their delivery will directly address key questions about the bombardment history of the inner Solar System. Regolith breccias, which are consolidated samples of the lunar regolith, were closed to further impact processing at the time they were assembled into rocks [1]. They are, therefore, time capsules of impact bombardment at different times through lunar history. Here we investigate the impact archive preserved in the Apollo 16 regolith breccias and compare this record to evidence of projectile species in other lunar samples.

Joy, K. H.↗
NASA NTRS2010

The Relationship of Magnetotail Flow Bursts and Ground Onset Signatures

It has been known for decades that auroral substorm onset occurs on (or at least near) the most equatorward auroral arc, which is thought to map to the near geosynchronous region. The lack of auroral signatures poleward of this arc prior to onset has been a major criticism of flow-burst driven models of substorm onset. The combined THEMIS 5 spacecraft in-situ and ground array measurements provide an unprecedented opportunity to examine the causal relationship between midtail plasma flows, aurora, and ground magnetic signatures. I first present an event from 2008 using multi-spectral all sky imager data from Gillam and in-situ data from THEMIS. The multispectral data indicate an equatorward moving auroral form prior to substorm onset. When this forms reaches the most equatorward arc, the arc brightens and an auroral substorm begins. The THEMIS data show fast Earthward flows prior to onset as well. I discuss further the association of flow bursts and Pi2 pulsations, in the con text of the directly-driven Pi2 model. This model directly links flows and Pi2 pulsations, providing an important constraint on substorm onset theories.

Kepko, Larry↗
NASA NTRS2010

Magnetic Topology of Coronal Hole Linkages

In recent work, Antiochos and coworkers argued that the boundary between the open and closed field regions on the Sun can be extremely complex with narrow corridors of open ux connecting seemingly disconnected coronal holes from the main polar holes, and that these corridors may be the sources of the slow solar wind. We examine, in detail, the topology of such magnetic configurations using an analytical source surface model that allows for analysis of the eld with arbitrary resolution. Our analysis reveals three important new results: First, a coronal hole boundary can join stably to the separatrix boundary of a parasitic polarity region. Second, a single parasitic polarity region can produce multiple null points in the corona and, more important, separator lines connecting these points. Such topologies are extremely favorable for magnetic reconnection, because it can now occur over the entire length of the separators rather than being con ned to a small region around the nulls. Finally, the coronal holes are not connected by an open- eld corridor of finite width, but instead are linked by a singular line that coincides with the separatrix footprint of the parasitic polarity. We investigate how the topological features described above evolve in response to motion of the parasitic polarity region. The implications of our results for the sources of the slow solar wind and for coronal and heliospheric observations are discussed.

Titov, V. S.↗
NASA NTRS2010

GPU Based Software Correlators - Perspectives for VLBI2010

Caused by historical separation and driven by the requirements of the PC gaming industry, Graphics Processing Units (GPUs) have evolved to massive parallel processing systems which entered the area of non-graphic related applications. Although a single processing core on the GPU is much slower and provides less functionality than its counterpart on the CPU, the huge number of these small processing entities outperforms the classical processors when the application can be parallelized. Thus, in recent years various radio astronomical projects have started to make use of this technology either to realize the correlator on this platform or to establish the post-processing pipeline with GPUs. Therefore, the feasibility of GPUs as a choice for a VLBI correlator is being investigated, including pros and cons of this technology. Additionally, a GPU based software correlator will be reviewed with respect to energy consumption/GFlop/sec and cost/GFlop/sec.

Hobiger, Thomas↗
NASA NTRS2011

Lightweight Magnetic Cooler With a Reversible Circulator

A design of a highly efficient and lightweight space magnetic cooler has been developed that can continuously provide remote/distributed cooling at temperatures in the range of 2 K with a heat sink at about 15 K. The innovative design uses a cryogenic circulator that enables the cooler to operate at a high cycle frequency to achieve a large cooling capacity. The ability to provide remote/distributed cooling not only allows flexible integration with a payload and spacecraft, but also reduces the mass of the magnetic shields needed. The active magnetic regenerative refrigerator (AMRR) system is shown in the figure. This design mainly consists of two identical magnetic regenerators surrounded by their superconducting magnets and a reversible circulator. Each regenerator also has a heat exchanger at its warm end to reject the magnetization heat to the heat sink, and the two regenerators share a cold-end heat exchanger to absorb heat from a cooling target. The circulator controls the flow direction, which cycles in concert with the magnetic fields, to facilitate heat transfer. Helium enters the hot end of the demagnetized column, is cooled by the refrigerant, and passes into the cold-end heat exchanger to absorb heat. The helium then enters the cold end of the magnetized column, absorbing heat from the refrigerant, and enters the hot-end heat exchanger to reject the magnetization heat. The efficient heat transfer in the AMRR allows the system to operate at a relatively short cycle period to achieve a large cooling power. The key mechanical components in the magnetic cooler are the reversible circulator and the magnetic regenerators. The circulator uses non-contacting, self-acting gas bearings and clearance seals to achieve long life and vibration- free operation. There are no valves or mechanical wear in this circulator, so the reliability is predicted to be very high. The magnetic regenerator employs a structured bed configuration. The core consists of a stack of thin GGG disks alternating with thin polymer insulating films. The structured bed reduces flow resistance in the regenerator and therefore the pumping work by the cryogenic circulator. This magnetic cooler will enable cryogenic detectors for sensing infrared, x-ray, gamma-ray, and submillimeter radiation in future science satellites, as well as the detector systems in the Constellation-X (Con-X) and the Single Aperture Far-Infrared observatory (SAFIR). Scientific ap p - lica tions for this innovation include cooling for x-ray micro calorimeter spectrometers used for microanalysis, cryogenic particle detectors, and superconducting tunnel junction de tectors for biomolecule mass spectrometry. The cooler can be scaled to provide very large cooling capacities at very low temperatures, ideal for liquid helium and liquid hydrogen productions.

Chen, Weibo↗
NASA NTRS2011

Hydrological Variations in Australia Recovered by GRACE High-Resolution Mascons Solutions

Australia represents a challenging region in which to study hydrological variations as recovered by the GRACE (Gravity Recovery And Climate Experiment) mission data. Much of Australia is characterized by relatively small hydrological signals, with large precipitation gradients between the North and the South. These signals are better recovered using innovative GRACE processing techniques such as high-resolution mascon solutions, which may help overcome the deficiencies in the standard GRACE data processing and filtering methods. We will show the power of using regional and global mas con solutions to recover hydrological variations from 2003 to 2011, as well as the oceanic mass variations in the surrounding regions. We will compare the GRACE signals with state of the art hydrology and ocean general circulation models, precipitation, soil moisture and groundwater data sets. We especially emphasize the gravity signatures observed during the decadal drought in the Murray-Darling river basin and the early 2011 floods in North-Western Australia.

Carabajal, Claudia C.↗
NASA NTRS2010

Improving Global Mass Flux Solutions from Gravity Recovery and Climate Experiment (GRACE) Through Forward Modeling and Continuous Time Correlation

We describe Earth's mass flux from April 2003 through November 2008 by deriving a time series of mas cons on a global 2deg x 2deg equal-area grid at 10 day intervals. We estimate the mass flux directly from K band range rate (KBRR) data provided by the Gravity Recovery and Climate Experiment (GRACE) mission. Using regularized least squares, we take into account the underlying process dynamics through continuous space and time-correlated constraints. In addition, we place the mascon approach in the context of other filtering techniques, showing its equivalence to anisotropic, nonsymmetric filtering, least squares collocation, and Kalman smoothing. We produce mascon time series from KBRR data that have and have not been corrected (forward modeled) for hydrological processes and fmd that the former produce superior results in oceanic areas by minimizing signal leakage from strong sources on land. By exploiting the structure of the spatiotemporal constraints, we are able to use a much more efficient (in storage and computation) inversion algorithm based upon the conjugate gradient method. This allows us to apply continuous rather than piecewise continuous time-correlated constraints, which we show via global maps and comparisons with ocean-bottom pressure gauges, to produce time series with reduced random variance and full systematic signal. Finally, we present a preferred global model, a hybrid whose oceanic portions are derived using forward modeling of hydrology but whose land portions are not, and thus represent a pure GRACE-derived signal.

Sabaka, T. J.↗
NASA NTRS2011

A New Global Mascon Solution Tuned for High-Latitude Ice Studies

A new global mascon solution has been developed with I-arc-degree spatial and IO-day temporal sampling. The global mas cons are estimated from the reduction of nearly 8 years of GRACE K-band range-rate data. Temporal and anisotropic spatial constraints have been applied for land, ocean and ice regions. The solution construction and tuning is focused towards the Greenland and Antarctic ice sheets (GIS and AIS) as well as the Gulf of Alaska mountain glaciers (GoA). Details of the solution development will be discussed, including the mascon parameter definitions, constraints, and the tuning of the constraint damping factor. Results will be presented, exploring the spatial and temporal variability of the ice sheets and GoA regions. A detailed error analysis will be discussed, including solution dependence on iteration, damping factor, forward modeling, and multitechnique comparisons. We also investigate the fundamental resolution of the solution and the spatial correlation of ice sheet inter-annual change. Finally, we discuss future improvements, including specific constraint application for the rest of the major land ice regions and improvements in solution regularization.

Luthcke, S. B.↗
NASA NTRS2011

The Enigma of Lunar Dust Transport

We will review the highly contrasting points of view regarding the ability of fine dust grains to become transported in the near-space lunar environment. While Surveyor and Apollo camera images suggest the presence of a horizon glow that has been provocatively interpreted as levitated and/or lofted dust, there is contrasting geological evidence to indicate that surface regolith has not been moved in a substantial way. While electric forces have been suggested as a driver for grain dynamics, recent detailed modeling of near-surface non-monotonic potentials would suggest grains could not get to large heights. While lofting models require submicron grains to hold/contain 100's of elementary charges, it can be shown analytical1y that a grain residing on a flat surface would have an extremely low probability of having even a single electron on its surface, Can these diametrically opposing viewpoints be reconciled? We will review the pros and cons on both sides. and suggest that the UVS and LDEX instrument on LADEE will provide key new insights on dust transport at the Moon.

Farrell, W. M.↗
NASA NTRS2011

Normalization of Gravitational Acceleration Models

Unlike the uniform density spherical shell approximations of Newton, the con- sequence of spaceflight in the real universe is that gravitational fields are sensitive to the nonsphericity of their generating central bodies. The gravitational potential of a nonspherical central body is typically resolved using spherical harmonic approximations. However, attempting to directly calculate the spherical harmonic approximations results in at least two singularities which must be removed in order to generalize the method and solve for any possible orbit, including polar orbits. Three unique algorithms have been developed to eliminate these singularities by Samuel Pines [1], Bill Lear [2], and Robert Gottlieb [3]. This paper documents the methodical normalization of two1 of the three known formulations for singularity-free gravitational acceleration (namely, the Lear [2] and Gottlieb [3] algorithms) and formulates a general method for defining normalization parameters used to generate normalized Legendre Polynomials and ALFs for any algorithm. A treatment of the conventional formulation of the gravitational potential and acceleration is also provided, in addition to a brief overview of the philosophical differences between the three known singularity-free algorithms.

Eckman, Randy A.↗
NASA NTRS2011

Solar Electric Propulsion (SEP) Tug Power System Considerations

Solar electric propulsion (SEP) technology is truly at the "intersection of commercial and military space" as well as the intersection of NASA robotic and human space missions. Building on the use of SEP for geosynchronous spacecraft station keeping, there are numerous potential commercial and military mission applications for SEP stages operating in Earth orbit. At NASA, there is a resurgence of interest in robotic SEP missions for Earth orbit raising applications, 1-AU class heliocentric missions to near Earth objects (NEOs) and SEP spacecraft technology demonstrations. Beyond these nearer term robotic missions, potential future human space flight missions to NEOs with high-power SEP stages are being considered. To enhance or enable this broad class of commercial, military and NASA missions, advancements in the power level and performance of SEP technologies are needed. This presentation will focus on design considerations for the solar photovoltaic array (PVA) and electric power system (EPS) vital to the design and operation of an SEP stage. The engineering and programmatic pros and cons of various PVA and EPS technologies and architectures will be discussed in the context of operating voltage and power levels. The impacts of PVA and EPS design options on the remaining SEP stage subsystem designs, as well as spacecraft operations, will also be discussed.

Kerslake, Thomas W.↗
NASA NTRS2012

The Valence of Iron in CM Chondrite Serpentine as Measured by Synchrotron Xanes

Fe-bearing phyllosilicates are the dominant product of aqueous alteration in carbonaceous chondrites, and serpentine is the most abundant phyllosilicate in CM2 chondrites that are the most abundant carbonaceous chondrite. Browning et al. predicted that Fe(3+)/(sum of Fe) ratios of serpentine in CM chondrites should change with progressive alteration. They proposed that progressive CM alteration is best monitored by evaluating the progress of Si and Fe3+ substitutions that necessarily attend the transition from end-member cronstedtite to serpentine. Their proposed Mineralogic Alteration Index, 2-(Fe(3+)/(2-Si)), was intended to highlight and utilize the relevant ex-change information in the stoichiometric phyllosilicate formulas based upon the coupled substitution of 2(Fe(3+), Al) = Si + (Mg, Fe(2+)...) in serpentine. The value of this ratio increases as alteration proceeds. We always wanted to directly test Browning s pre-diction through actual measurements of the Fe3+ con-tent of serpentine at the micron scale appropriate to EPMA analyses (Zega et al. have measured it at much finer scale), and this test can now be made using Synchrotron Radiation X-ray Absorption Near-Edge Structure (SR-XANES). Thus, we have recently begun investigation with CMs that span a large portion of the range of observed aqueous alteration, and we first analyzed Murray, Nogoya, and ALH84029 by SR-XANES. However, we did not find clear correlation between Fe3+/(sum of Fe) ratios of serpentine and their alteration degrees. We thus analyzed serpentine in three more CMs and here report their Fe3+/(sum of Fe) ratios in comparison with our previous results.

Mikouchi, T.↗
NASA NTRS2012

Lunar Floor-Fractured Craters: Classification, Distribution and Implications for Magmatism and Shallow Crustal Structure

Floor-fractured craters (FFCs) are a class of lunar craters defined by their distinctly shallow, often plate-like floors, and combinations of radial, con-centric, and polygonal floor-fractures; a variety of other interior features are often observed, such as moats, ridges, small dark-haloed pits, and patches of mare material. They were first classified by Schultz [1] , who recognized eight overall types of floor-fractured crater. These eight subtypes have widely differing appearances, a factor that could provide insight into formation mechanisms (different manifestations of the same mechanism, or indicators of varying formation mechanisms). Two formation mechanisms for FFCs were initially proposed: 1) magmatic intrusion [1], in which magma rising toward the surface in dikes encountered low-density breccia lenses beneath crater floors and spread laterally to form sills, raising and fracturing the crater floor. 2) viscous relaxation [2], in which the properties of the crust permitted viscous flow in the vicinity of the crater, causing long-wavelength relaxation of the topography and uplift and fracturing of the crater floor. Critical to distinguishing between these two end-member hypotheses and identifying others is a quantitative assessment of the topography of FFCs and knowledge of their regional and local settings. The purpose of this study is to use newly available Lunar Reconnaissance Orbiter (LRO) Lunar Orbiter Laser Altimeter (LOLA) altimeter and Lunar Reconnaissance Orbiter Camera (LROC) image data to provide an updated global catalog of the locations, classes, morphometric and morphologic characteristics of all lunar floor-fractured craters. We use the excellent 8-class system initially described in Schultz [1] as a starting point for classification and the enhanced LOLA/LROC data sets to examine and categorize all FFCs; we found evidence for a new FFC class, discernably different from the previously existing types. Our approach, and the global categorization of all FFCs, permits the spatial distribution of each FFC-subtype to be plotted and assessed allowing for further investigation into FFC formation mechanisms. Upon completion, the data set will be made available on our web site at http://www.planetary.brown.edu/html_pages/data.htm.

Jozwiak, L. M.↗
NASA NTRS2012

Communicating the Threat of a Tropical Cyclone to the Eastern Range

The 45th Weather Squadron (45 WS) has developed a tool to help visualize the Wind Speed Probability product from the National Hurricane Center (NHC) and to help communicate that information to space launch customers and decision makers at the 45th Space Wing (45 SW) and Kennedy Space Center (KSC) located in east central Florida. This paper reviews previous work and presents the new visualization tool, including initial feedback as well as the pros and cons. The NHC began issuing their Wind Speed Probability product for tropical cyclones publicly in 2006. The 45 WS uses this product to provide a threat assessment to 45 SW and KSC leadership for risk evaluations with an approaching tropical cyclone. Although the wind speed probabilities convey the uncertainty of a tropical cyclone well, communicating this information to customers is a challenge. The 45 WS continually strives to provide the wind speed probability information to customers in a context which clearly communicates the threat of a tropical cyclone. First, an intern from the Florida Institute of Technology (FIT) Atmospheric Sciences department, sponsored by Scitor Corporation, independently evaluated the NHC wind speed probability product. This work was later extended into a M.S. thesis at FIT, partially funded by Scitor Corporation and KSC. A second thesis at FIT further extended the evaluation partially funded by KSC. Using this analysis, the 45 WS categorized the probabilities into five probability interpretation categories: Very Low, Low, Moderate, High, and Very High. These probability interpretation categories convert the forecast probability and forecast interval into easily understood categories that are consistent across all ranges of probabilities and forecast intervals. As a follow-on project, KSC funded a summer intern to evaluate the human factors of the probability interpretation categories, which ultimately refined some of the thresholds. The 45 WS created a visualization tool to express the timing and risk for multiple locations in a single graphic. Preliminary results on an on-going project by FIT will be included in this paper. This project is developing a new method of assigning the probability interpretation categories and updating the evaluation of the performance of the NHC wind speed probability analysis.

Winters, Katherine A.↗
NASA NTRS2012

Development of a Portfolio Management Approach with Case Study of the NASA Airspace Systems Program

A portfolio management approach was developed for the National Aeronautics and Space Administration s (NASA s) Airspace Systems Program (ASP). The purpose was to help inform ASP leadership regarding future investment decisions related to its existing portfolio of advanced technology concepts and capabilities (C/Cs) currently under development and to potentially identify new opportunities. The portfolio management approach is general in form and is extensible to other advanced technology development programs. It focuses on individual C/Cs and consists of three parts: 1) concept of operations (con-ops) development, 2) safety impact assessment, and 3) benefit-cost-risk (B-C-R) assessment. The first two parts are recommendations to ASP leaders and will be discussed only briefly, while the B-C-R part relates to the development of an assessment capability and will be discussed in greater detail. The B-C-R assessment capability enables estimation of the relative value of each C/C as compared with all other C/Cs in the ASP portfolio. Value is expressed in terms of a composite weighted utility function (WUF) rating, based on estimated benefits, costs, and risks. Benefit utility is estimated relative to achieving key NAS performance objectives, which are outlined in the ASP Strategic Plan.1 Risk utility focuses on C/C development and implementation risk, while cost utility focuses on the development and implementation portions of overall C/C life-cycle costs. Initial composite ratings of the ASP C/Cs were successfully generated; however, the limited availability of B-C-R information, which is used as inputs to the WUF model, reduced the meaningfulness of these initial investment ratings. Development of this approach, however, defined specific information-generation requirements for ASP C/C developers that will increase the meaningfulness of future B-C-R ratings.

Neitzke, Kurt W.↗
NASA NTRS2012

Lidar Measurements for Desert Dust Characterization: An Overview

We provide an overview of light detection and ranging (lidar) capability for describing and characterizing desert dust. This paper summarizes lidar techniques, observations, and fallouts of desert dust lidar measurements. The main objective is to provide the scientific community, including non-practitioners of lidar observations with a reference paper on dust lidar measurements. In particular, it will fill the current gap of communication between research-oriented lidar community and potential desert dust data users, such as air quality monitoring agencies and aviation advisory centers. The current capability of the different lidar techniques for the characterization of aerosol in general and desert dust in particular is presented. Technical aspects and required assumptions of these techniques are discussed, providing readers with the pros and cons of each technique. Information about desert dust collected up to date using lidar techniques is reviewed. Lidar techniques for aerosol characterization have a maturity level appropriate for addressing air quality and transportation issues, as demonstrated by some first results reported in this paper

Mona, L.↗
NASA NTRS2012

Alterations of Cellular Immune Reactions in Crew Members Overwintering in the Antarctic Research Station Concordia

Background: Concordia Station is located inside Antarctica about 1000km from the coast at an altitude of 3200m (Dome C). Hence, individuals living in this harsh environment are exposed to two major conditions: 1.) hypobaric hypoxia and 2.) confinement and extreme isolation. Both hypoxia and confinement can affect human immunity and health, and are likely to be present during exploration class space missions. This study focused on immune alterations measured by a new global immunity test assay, similar to the phased out delayed type hypersensitivity (DTH) skin test. Methods: After informed written consent 14 healthy male subjects were included to the CHOICE-study (Consequences-of-longterm-Confinement-and-Hypobaric-HypOxia-on-Immunity-in-the Antarctic-Concordia-Environment). Data collection occurred during two winter-over periods lasting each one year. During the first campaign 6 healthy male were enrolled followed by a second campaign with 8 healthy males. Blood was drawn monthly and incubated for 48h with various bacterial, viral and fungal antigens followed by an analysis of plasma cytokine levels (TNF-alpha, IL2, IFN-gamma, IL10). As a control, blood was incubated without stimulation ("resting condition"). Goals: The scope of this study was to assess the consequences of hypoxia and confinement on cellular immunity as assessed by a new in vitro DTH-like test. Results: Initial results indicate that under resting conditions the in vitro DTH-like test showed low cytokine levels which remained almost unchanged during the entire observation period. However, cytokine responses to viral, bacterial and fungal antigens were remarkably reduced at the first month after arrival at Concordia when compared to levels measured in Europe prior to departure for Antarctica. With incrementing months of confinement this depressed DTH-like response tended to reverse, and in fact to show an "overshooting" immune reaction after stimulation. Conclusion: The reduced in vitro DTH-like test response in the early phase of Antarctic wintering over con rms distinct immune suppressive effects seen after (sub-)acute hypobaric hypoxia. The reversal and overshooting reaction of cellular immune responses upon stimulation, but not the resting state, indicate either a) priming of immune answers and/or b) an uncoupled or disregulated control of cellular immune answers by auto-, para- and endocrine pathways. Further analyses and correlations are warranted. Acknowledgement: Supported by the European Space Agency (ESA), the French (IPEV) and Italian (PNRA) polar institutes, the German National Space Program (DLR, 50WB0719/WB0919), by BELSPO/PROEDEX/ESA (C90-380/-391), NASA and by the Concordia crews who have participated with great enthusiasm.

Crucian, Brian↗
NASA NTRS2012

Analog Design for Digital Deployment of a Serious Leadership Game

This paper presents the design, development, and user testing of a leadership development simulation. The authors share lessons learned from using a design process for a board game to allow for quick and inexpensive revision cycles during the development of a serious leadership development game. The goal of this leadership simulation is to accelerate the development of leadership capacity in high-potential mid-level managers (GS-15 level) in a federal government agency. Simulation design included a mixed-method needs analysis, using both quantitative and qualitative approaches to determine organizational leadership needs. Eight design iterations were conducted, including three user testing phases. Three re-design iterations followed initial development, enabling game testing as part of comprehensive instructional events. Subsequent design, development and testing processes targeted digital application to a computer- and tablet-based environment. Recommendations include pros and cons of development and learner testing of an initial analog simulation prior to full digital simulation development.

Maxwell, Nicholas↗