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At least 757 records · Page 42

Focused transport of energetic particles along magnetic field lines draped around a coronal mass ejection

Evidence is presented for focused transport of energetic particles along magnetic field lines draped around a coronal mass ejection. This evidence was obtained with the University of Maryland/Max-Planck-Institute experiment on the ISEE-3 spacecraft during the decay phase of the June 6, 1979, solar particle event. During the early portion of the decay phase of this event, interplanetary magnetic field lines were apparently draped around a coronal mass ejection, leading to a small focusing length on the western flank where ISEE 3 was located. A period of very slow decrease of particle intensity was observed, along with large sunward anisotropy in the solar wind frame, which is inconsistent with predictions of the standard Fokker-Planck equation models for diffusive transport. It was found possible to fit the observations, assuming that focused transport dominates and that the particle pitch angle scattering is isotropic.

Tan, L. C.↗

Cratering in glasses impacted by debris or micrometeorites

Mechanical strength measurements on five glasses and one glass-ceramic exposed on LDEF revealed no damage exceeding experimental limits of error. The measurement technique subjected less than 5 percent of the sample surface area to stresses above 90 percent of the failure strength. Seven micrometeorite or space debris impacts occurred at locations which were not in that portion of the sample subjected to greater than 90 percent of the applied stress. As a result of this, the impact events on the sample were not detected in the mechanical strength measurements. The physical form and structure of the impact sites was carefully examined to determine the influence of those events upon stress concentration associated with the impact and the resulting mechanical strength. The size of the impact site, insofar as it determines flaw size for fracture purposes, was examined. Surface topography of the impacts reveals that six of the seven sites display impact melting. The classical melt crater structure is surrounded by a zone of fractured glass. Residual stresses arising from shock compression and from cooling of the fused zone cannot be included in the fracture mechanics analyses based on simple flaw size measurements. Strategies for refining estimates of mechanical strength degradation by impact events are presented.

Wiedlocher, David E.↗

Traveling compression region observed in the mid-tail lobes near substorm expansion phase onset

The characteristics of traveling compression regions (TCRs) in the midtail lobes are examined. Through the use of the AL index, isolated substorm events with well developed expansion phases are selected. The TCR events which feature a field compression coincident with modified Bz variations are categorized into different types, and the magnetic variations are interpreted in terms of the relative location of the point of observation to the plasmoid at the time of release and the effects of tail flaring. In order to understand the relationship between the plasmoid release time and the substorm onset time, the time difference between the different types of TCR and the substorm onset determined by Pi 2 pulsations at mid-latitude ground stations, is examined. The results suggest that the downtail release of most of the plasmoids created earthwards of -38 earth radii occurs at almost the same distance as the substorm onset.

Taguchi, S.↗

The Third BATSE Gamma-Ray Burst Catalog

The Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray Observatory (CGRO) has triggered on 1122 cosmic gamma-ray bursts between 1991 April 19 and 1994 September 19. These events constitute the Third BATSE (3B) burst catalog. This catalog includes the events previously reported in the 2B catalog, which covered the time interval 1991 April 19 to 1993 March 9. We present tables of the burst occurrence times, locations, peak fluxes, fluences, and durations. In general, results from previous BATSE catalogs are confirmed here with greater statistical significance. The angular distribution is consistent with isotropy. The mean galactic dipole and quadrupole moments are within 0.6 a and 0.3 a, respectively, of the values expected for isotropy. The intensity distribution is not consistent with a homogeneous distribution of burst sources, with V/V(sub max) = 0.33 +/- 0.01. The duration distribution (T(sub 90)) exhibits bimodality, with peaks at approx. 0.5 and approx. 30 s. There is no compelling evidence for burst repetition, but only weak limits can be placed on the repetition rate.

Meegan, Charles A.↗

The Spirit Rover's Athena science investigation at Gusev Crater, Mars

The Mars Exploration Rover Spirit and its Athena science payload have been used to investigate a landing site in Gusev crater. Gusev is hypothesized to be the site of a former lake, but no clear evidence for lacustrine sedimentation has been found to date. Instead, the dominant lithology is basalt, and the dominant geologic processes are impact events and eolian transport. Many rocks exhibit coatings and other characteristics that may be evidence for minor aqueous alteration. Any lacustrine sediments that may exist at this location within Gusev apparently have been buried by lavas that have undergone subsequent impact disruption.

Mars↗

Dynamic Modeling of Ascent Abort Scenarios for Crewed Launches

For the last 30 years, the United States's human space program has been focused on low Earth orbit exploration and operations with the Space Shuttle and International Space Station programs. After nearly 50 years, the U.S. is again working to return humans beyond Earth orbit. To do so, NASA is developing a new launch vehicle and spacecraft to provide this capability. The launch vehicle is referred to as the Space Launch System (SLS) and the spacecraft is called Orion. The new launch system is being developed with an abort system that will enable the crew to escape launch failures that would otherwise be catastrophic as well as probabilistic design requirements set for probability of loss of crew (LOC) and loss of mission (LOM). In order to optimize the risk associated with designing this new launch system, as well as verifying the associated requirements, NASA has developed a comprehensive Probabilistic Risk Assessment (PRA) of the integrated ascent phase of the mission that includes the launch vehicle, spacecraft and ground launch facilities. Given the dynamic nature of rocket launches and the potential for things to go wrong, developing a PRA to assess the risk can be a very challenging effort. Prior to launch and after the crew has boarded the spacecraft, the risk exposure time can be on the order of three hours. During this time, events may initiate from either of the spacecraft, the launch vehicle, or the ground systems, thus requiring an emergency egress from the spacecraft to a safe ground location or a pad abort via the spacecraft's launch abort system. Following launch, again either the spacecraft or the launch vehicle can initiate the need for the crew to abort the mission and return to the home. Obviously, there are thousands of scenarios whose outcome depends on when the abort is initiated during ascent as to how the abort is performed. This includes modeling the risk associated with explosions and benign system failures that require aborting a spacecraft under very dynamic conditions, particularly in the lower atmosphere, and returning the crew home safely. This paper will provide an overview of the PRA model that has been developed of this new launch system, including some of the challenges that are associated with this effort. Key Words: PRA, space launches, human space program, ascent abort, spacecraft, launch vehicles

Bigler, Mark↗

Cost-Effective Icy Bodies Exploration using Small Satellite Missions

It has long been known that Saturn's moon Enceladus is expelling water-rich plumes into space, providing passing spacecraft with a window into what is hidden underneath its frozen crust. Recent discoveries indicate that similar events could also occur on other bodies in the solar system, such as Jupiter's moon Europa and the dwarf planet Ceres in the asteroid belt. These plumes provide a possible giant leap forward in the search for organics and assessing habitability beyond Earth, stepping stones toward the long-term goal of finding extraterrestrial life. The United States Congress recently requested mission designs to Europa, to fit within a cost cap of $1B, much less than previous mission designs' estimates. Here, innovative cost-effective small spacecraft designs for the deep-space exploration of these icy worlds, using new and emerging enabling technologies, and how to explore the outer solar system on a budget below the cost horizon of a flagship mission, are investigated. Science requirements, instruments selection, rendezvous trajectories, and spacecraft designs are some topics detailed. The mission concepts revolve around a comparably small-sized and low-cost Plume Chaser spacecraft, instrumented to characterize the vapor constituents encountered on its trajectory. In the event that a plume is not encountered, an ejecta plume can be artificially created by a companion spacecraft, the Plume Maker, on the target body at a location timed with the passage of the Plume Chaser spacecraft. Especially in the case of Ceres, such a mission could be a great complimentary mission to Dawn, as well as a possible future Europa Clipper mission. The comparably small volume of the spacecraft enables a launch to GTO as a secondary payload, providing multiple launch opportunities per year. Plume Maker's design is nearly identical to the Plume Chaser, and fits within the constraints for a secondary payload launch. The cost-effectiveness of small spacecraft missions enables the exploration of multiple solar system bodies in reasonable timeframes despite budgetary constraints, with only minor adaptations. The work presented here is a summary of concepts targeting icy bodies, such as Europa and Ceres, which have been developed over the last year at NASA Ames Research Center's Mission Design Division. The platforms detailed in this work are also applicable to the cost-effective exploration of many other small icy bodies in the solar system.

Mission Design↗

Solar Flare X-Ray Source Motion as a Response to Electron Spectral Hardening

Context. Solar flare hard X-rays (HXRs) are thought to be produced by nonthermal coronal electrons stopping in the chromosphere, or remaining trapped in the corona. The collisional thick target model (CTTM) predicts that more energetic electrons penetrate to greater column depths along the flare loop. This requires that sources produced by harder power-law injection spectra should appear further down the legs or footpoints of a flareloop. Therefore, the frequently observed hardening of the injected power-law electron spectrum during flare onset should be concurrent with a descending hard X-ray source. Aims. To test this implication of the CTTM by comparing its predicted HXR source locations with those derived from observations of a solar flare which exhibits a nonthermally-dominated spectrum before the peak in HXRs, known as an early impulsive event. Methods. HXR images and spectra of an early impulsive C-class flare were obtained using the Ramaty High-Energy Solar Spectroscopic Imager (RHESSI). Images were reconstructed to produce HXR source height evolutions for three energy bands. Spatially-integrated spectral analysis was performed to isolate nonthermal emission, and to determine the power-law index of the electron injection spectrum. The observed height-time evolutions were then fit with CTTM-based simulated heights for each energy, using the electron spectral indices derived from the RHESSI spectra. Results. The flare emission was found to be dominantly nonthermal above approx. 7 keV, with emission of thermal and nonthermal X-rays likely to be simultaneously observable below that energy. The density structure required for a good match between model and observed source heights agreed with previous studies of flare loop densities. Conclusions. The CTTM has been used to produce a descent of model HXR source heights that compares well with observations of this event. Based on this interpretation, downward motion of nonthermal sources should indeed occur in any flare where there is spectral hardening in the electron distribution during a flare. However, this would often be masked by thermal emission associated with flare plasma pre-heating. As yet, flare models that predict transfer of energy from the corona to the chromosphere by means other than a flux of nonthermal electrons do not predict this observed source descent. Therefore, flares such as this will be key in explaining this elusive energy transfer process.

X-rays↗

Laboratory Scale Testing of Ignition Overpressure for Space Vehicle Launch Pad Environments

A scale model of a NASA representative space vehicle is used to develop a refined estimate of the transient pressure loads that are expected to form at the base of the vehicle in the event of a vapor cloud explosion. Flammable vapor clouds are known to form prior to engine startup due to the significant amount of unburned hydrogen that is ejected from the combustion chamber. In the event of a vapor cloud explosion, the vehicle and payload must be able to withstand the resulting overpressure waves. The study comprises an array of pressure sensors located along the base heat shield of the scale model space vehicle as well as the interior wall and throat plug plane of the solid rocket booster. A spark source generator is used to simulate the overpressure wave produced by a vapor cloud explosion while measurements are acquired with and without the effect of a mobile launcher. Time- resolved schlieren images of the simulated vapor cloud explosion reveal the path and impact of both the initial wave and several reflected waves on the various components at the base of the space vehicle. In some instances, the reflected waves superpose to create waves that are higher in amplitude than the initial overpressure wave. A time frequency analysis of the pressure waveforms measured inside the solid rocket booster reveal a ring down tone corresponding to a standing wave that is four times the length of the nozzle.

Tinney, Charles E.↗

Assessing Dual-Polarization Radar Estimates of Extreme Rainfall During Hurricane Harvey

Hurricane Harvey hit the Texas Gulf Coast as a major hurricane on August 25, 2017 before exiting the state as a tropical storm on August 29, 2017. Left in its wake was historic flooding, with some locations measuring more than 60 inches of rain over a five-day period. The WSR-88D radar (KHGX) maintained operations for the entirety of the event. Rain gauge data from the Harris County Flood Warning System (HCFWS) was used for validation with the full radar data set to retrieve daily and event-total precipitation estimates for the period August 25-29, 2017. The KHGX precipitation estimates were then compared to the HCFWS gauges. Three different hybrid polarimetric rainfall retrievals were used, along with attenuation-based retrieval that employs the radar-observed differential propagation. An advantage of using a attenuation-based retrieval is its immunity to partial beam blockage and calibration errors in reflectivity and differential reflectivity. All of the retrievals are susceptible to changes in the observed Drop Size Distribution (DSD). No in situ DSD data were available over the study area, so changes in the DSD were interpreted by examining the observed radar data. We examined the parameter space of two key values in the attenuation retrieval to test the sensitivity of the rain retrieval. Selecting a value of α=0.015 and β=0.600 and β=0.625 provided the best overall results, relative to the gauges, but more work needs to be done to develop an automated technique to account for changes in the ambient DSD.

David B Wolff↗

Buckling and Failure Tests of a Subscale Composite Cylinder

A subscale solid laminate composite cylinder 31.5-in. diameter and 47.8 in. long with a [23/0/-23]4S layup known as NDL-1 was designed to fail in buckling and tested in axial compression to collapse twice. The proposed paper will focus on comparing the behavior of NDL-1 from the first test to failure (TTF-1) and the second test to failure (TTF-2). NDL-1 had a peak load of 466.3 kips during TTF-1 and a peak load of 390.4 kips, 15.5% lower, but with a similar stiffness, during TTF-2. Failure initiated at the 200º circumferential location in TTF-1, and at the 30º circumferential location in TTF-2. Though failure initiated at different locations, a similar radial deformation pattern was present just prior to collapse in TTF-1 and TTF-2. A shallow delamination occurred due to the initial failure event in TTF-1, and the damage had no influence on the response of NDL-1 during TTF-2. In the end, it was determined that NDL-1 failed in buckling during TTF-1 and TTF-2, and the second test to failure of NDL-1 highlighted interesting observations with respect to the effect of damage.

Buckling↗

Independent Analyses of Galveston QSF18 Social Survey

A set of independent analyses was performed of the findings of NASA’s QSF18 data collection exercise in Galveston, TX. These analyses included development of regression-based and other dosage-response relationships between the prevalence of annoyance with low-amplitude sonic booms and Perceived Level measures of single event and cumulative exposure. They also included detailed analyses of the effects of panelist attrition; of participation reminder messages sent to panelists; the ability to determine panelist locations at the time of exposure; and the effects of rattle and vibration on annoyance judgments, among other topics. The report summarizes the implications of its findings for the design of studies of community response to carpet booms created during future deployments of NASA’s X-59 aircraft, and recommends several design measures to improve the efficiency of data collection.

sonic boom↗

Satellites Support Disaster Response to Storm-Driven Landslides

High winds and flooding storm surges driven by tropical cyclones cause some of the deadliest and most damaging weather-related conditions around the world. The rainfall that cyclones bring compounds these conditions and, in hilly or mountainous areas, can trigger landslides that cause even more widespread and devastating impacts. When extreme precipitation occurs over short time frames, hillslopes may become saturated and critically unstable. The most intense storms can trigger thousands of landslides in mountainous areas, as was dramatically illustrated in Puerto Rico in September 2017, when Hurricane Maria’s rains left the landscape scarred by roughly 40,000 landslides. Before and during a major cyclone, disaster responders need information about where landslides are likely to occur. In the aftermath, locating landslides quickly helps authorities direct resources to where they are most needed to save people and critical infrastructure. However, this information is often unavailable during an event response or is presented only for small regions, constraining the effectiveness of response efforts.

Robert Emberson↗

Cluster Analysis of Thermal Icequakes Using the Seismometer to Investigate Ice and Ocean Structure (SIIOS): Implications for Ocean World Seismology

Ocean Worlds are of high interest to the planetary community due to the potential habitability of their subsurface oceans. Over the next few decades several missions will be sent to ocean worlds including the Europa Clipper, Dragonfly, and possibly a Europa lander. The Dragonfly and Europa lander missions will carry seismic payloads tasked with detecting and locating seismic sources. The Seismometer to Investigate Ice and Ocean Structure (SIIOS) is a NASA PSTAR funded project that investigates ocean world seismology using terrestrial analogs. The goals of the SIIOS experiment include quantitatively comparing flight-candidate seismometers to traditional instruments, comparing single-station approaches to a small-aperture array, and characterizing the local seismic environment of our field sites. Here we present an analysis of detected local events at our field sites at Gulkana Glacier in Alaska and in Northwest Greenland approximately 80 km North of Qaanaaq, Greenland. Both field sites passively recorded data for about two weeks. We deployed our experiment on Gulkana Glacier in September 2017 and in Greenland in June 2018. At Gulkana there was a nearby USGS weather station which recorded wind data. Temperature data was collected using the MERRA satellite. In Greenland we deployed our own weather station to collect temperature and wind data. Gulkana represents a noisier and more active environment. Temperatures fluctuated around 0°C, allowing for surface runoff to occur during the day. The glacier had several moulins, and during deployment we heard several rockfalls from nearby mountains. In addition to the local environment, Gulkana is located close to an active plate boundary (relative to Greenland). This meant that there were more regional events recorded over two weeks, than in Greenland. Greenland’s local environment was also quieter, and less active. Temperatures remained below freezing. The Greenland ice was much thicker than Gulkana (~850 m versus ~100 m) and our stations were above a subglacial lake. Both conditions can reduce event detections from basal motion. Lastly, we encased our Greenland array in an aluminum vault and buried it beneath the surface unlike our array in Gulkana where the instruments were at the surface and covered with plastic bins. The vault further insulated the array from thermal and atmospheric events.

Marusiak, A. G.↗

Rayleigh/raman Greenland Lidar Observations of Atmospheric Temperature During a Major Arctic Stratospheric Warming Event

Between Jan. 22 1991 to Feb. 5 1991, we made numerous observations of atmospheric temperature profiles between 10 and 70 km by using the combination of Rayleigh and Raman lidar systems contained in the PL Mobile Lidar Facility located at the National Science Foundation Incoherent Radar Facility of Sondrestrom in Greenland. The purpose of these measurements was to observe the dynamics of the winter Arctic stratosphere and mesosphere regions during a winter period from the succession of temperature profiles obtained in our campaign observations. Various aspects of this investigation are presented.

Meriwether, John W.↗

Comparisons Between Unsteady Aerodynamic Events in a Gas Turbine Generator and an Identical Compressor Rig

Extensive testing done on a T55-L-712 turboshaft engine compressor in a compressor test rig is being followed by engine tests in progress as part of the Army Non-Recoverable Stall Program. Goals include a greater understanding of the gas turbine engine start cycle and compressor/engine operation in the regions 'beyond' the normal compressor stall line (rotating stall/surge). Rig steady state instrumentation consisted of 497 steady state pressure sensors and 153 temperature sensors. Engine instrumentation was placed in similar radial/axial locations and consists of 122 steady state pressure sensors and 65 temperature sensors. High response rig instrumentation consisted of 34 wall static pressure transducers. Rig and engine high response pressure transducers were located in the same axial/radial/circumferential locations in front of the first three stages. Additional engine high response instrumentation was placed in mach probes in front of the engine and on the compressor hub. This instrumentation allows for the generation of detailed stage characteristics, overall compressor mapping, and detailed analysis of dynamic compressor events.

Owen, A. Karl↗

The International Space Station: A Unique Platform for Remote Sensing of Natural Disasters

Assembly of the International Space Station (ISS) was completed in 2012, and the station is now fully operational as a platform for remote sensing instruments tasked with collecting scientific data about the Earth system. Remote sensing systems are mounted inside the ISS, primarily in the U.S. Destiny Module's Window Observational Research Facility (WORF), or are located on the outside of the ISS on any of several attachment points. While NASA and other space agencies have had remote sensing systems orbiting Earth and collecting publicly available data since the early 1970s, these sensors are carried onboard free-flying, unmanned satellites. These satellites are traditionally placed into Sun-synchronous polar orbits that allow imaging of the entire surface of the Earth to be repeated with approximately the same Sun illumination (typically local solar noon) over specific areas, with set revisit times that allow uniform data to be taken over long time periods and enable straightforward analysis of change over time. In contrast, the ISS has an inclined, Sun-asynchronous orbit (the solar illumination for data collections over any location changes as the orbit precesses) that carries it over locations on the Earth between approximately 52degnorth and 52deg south latitudes (figure 1). The ISS is also unique among NASA orbital platforms in that it has a human crew. The presence of a crew provides options not available to robotic sensors and platforms, such as the ability to collect unscheduled data of an unfolding event using handheld digital cameras as part of the Crew Earth Observations (CEO) facility and on-the-fly assessment of environmental conditions, such as cloud cover, to determine whether conditions are favorable for data collection. The crew can also swap out internal sensor systems installed in the WORF as needed. The ISS orbit covers more than 90 percent of the inhabited surface of the Earth, allowing the ISS to pass over the same ground locations at different times of the day and night. This is important for two reasons: 1) certain surface processes (i.e., development of coastal fog banks) occur at times other than local solar noon, making it difficult to collect relevant data from traditional satellite platforms, and 2) it provides opportunities for the ISS to collect data for short-duration events, such as natural disasters, that polar-orbiting satellites may miss due to their orbital dynamics - in essence, the ISS can be "in the right place at the right time" to collect data. An immediate application of ISS remote sensing data collection is that the data can be used to provide information for humanitarian aid after a natural disaster. This activity contributes directly to the station's Benefits to Humanity mission. The International Charter, Space and Major Disasters (also known as the International Disaster Charter, or IDC) is an agreement between agencies of several countries to provide - on a best-effort basis - remotely sensed data related to natural disasters to requesting countries in support of disaster response. In the United States, the lead agency for interaction with the IDC is the United States Geological Survey (USGS); when an IDC request, or activation, is received, the USGS notifies the science teams for NASA instruments with targeting information for data collection. In the case of the ISS, Earth scientists in the JSC ARES Directorate, in association with the ISS Program Science Office, coordinate targeting and data collection with the USGS. If data is collected, it is passed back to the USGS for posting on its Hazards Data Distribution System and made available for download. The ISS was added to the USGS's list of NASA remote sensing assets that could respond to IDC activations in May 2012. Initially, the NASA ISS sensor systems available to respond to IDC activations included the ISS Agricultural Camera (ISSAC), an internal multispectral visible-near infrared wavelength system mounted in the WORF; CEO, a project that collects imagery through the ISS windows using off-the-shelf handheld digital visible-wavelength cameras; and the Hyperspectral Imager for the Coastal Oceans (HICO), a visible to near-infrared system mounted externally on the Japanese Experiment Module - Exposed Facility. Since May 2012, there have been 37 IDC activations; ISS sensor systems have collected data for 10 of these events.

Stefanov, William L.↗

The International Space Station Space Radiation Environment: Avionics Systems Performance in Low-Earth Orbit Single Event Effects (SEE) Environments

Single event effects (SEE) are those errors, anomalies, or failures in microelectronic devices caused by the passage of a single energetic charged particle through the device. Spacecraft SEE environments consist primarily of energetic charged particles; both primary particles originating in the natural environment and secondary particles (including secondary neutrons) produced by nuclear reactions of primary particles with spacecraft materials. The energetic charged particle components (electrons, protons, and atomic nuclei) of the spacecraft SEE environment include galactic cosmic rays (GCR), and planetary radiation belt charged particles, as well as solar energetic particle event (SPE) charged particles. The International Space Station (ISS) orbital altitude and inclination (~350 km to ~420 km at 51.6o inclination) results in a spacecraft SEE environment that varies dramatically with the location in Earth?s geomagnetic field. Geomagnetic GCR shielding diminishes with distance from the geomagnetic equator. Near + 51.6o latitude the ISS GCR environment has a high degree of similarity to the interplanetary GCR environment in cis-Lunar space.SEE environments supporting ISS avionics systems design, development, test, and verification are documented in SSP-30512, Space Station Ionizing Radiation Design Environment. Comparisons of overall ISS avionics systems in-flight performance with pre-flight verification report predictions have been previously reported and meet or exceed expectations in all cases.In this paper we report the results of more detailed investigations of the effects of geographic location, altitude, solar cycle, and shielding mass effects on the in-flight SEE performance of the ISS command and data handling system during the past 17 years. In addition, we report on the preflight testing and in-flight performance of the commercial-off-the-shelf lap top computers used on ISS. Finally, we present an assessment of ISS as an avionics SEE test and flight demonstration platform for exploration hardware destined for the cis-lunar or other inner solar system environments.

International Space Station↗