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At least 433 records · Page 24

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NASA NTRS2005

Origin and Evolution of Deep Plasmaspheric Notches

Deep plasmaspheric notches can extend over more than 2 R(sub E) in radial distance and 3 hours MLT in the magnetic equatorial plane, as observed by the extreme ultraviolet (EUV) imager on the IMAGE mission. They are among the largest evacuated features in the exterior plasmaspheric boundary. They can last for days and exhibit a variety of shapes. It appears that weak convection and limited erosion precedes notch formation at the westward, near-Earth edge of the convection plume. Eighteen clear notch events were found and analyzed in 2000. Among these events, notches were found to drift as slowly as 44% of corotation. In only one case was a notch found to drift at the corotation rate within measurement error. On average, these notches drift at about 21.5 h d(sup -1) or 90% of the corotational rate. Notches sometimes exhibit an interior structure that appears as an extended prominence of dense plasma, which forms a W- or M-like feature in IMAGE/EUV images, depending on viewing perspective. Initial modeling suggests that notches and notch prominences may be caused in part by intense small-scale potential structures that result from the localized injection of ring current plasma. Plasma filling rates during recovery are examined in three L shell ranges from L = 2 to L = 3.5 with rates ranging from 5 to 140 cm(sup -3) d(sup -1). Plasma loss during a minor substorm is found to extend to surprisingly low L shell with rates ranging from 100 to 130 cm(sup -3) d(sup -1) across the L shells examined.

Gallagher, D. L.↗

NASA NTRS2008

Revitalizing the Space Shuttle's Thermal Protection System with Reverse Engineering and 3D Vision Technology

The Space Shuttle is protected by a Thermal Protection System (TPS) made of tens of thousands of individually shaped heat protection tile. With every flight, tiles are damaged on take-off and return to earth. After each mission, the heat tiles must be fixed or replaced depending on the level of damage. As part of the return to flight mission, the TPS requirements are more stringent, leading to a significant increase in heat tile replacements. The replacement operation requires scanning tile cavities, and in some cases the actual tiles. The 3D scan data is used to reverse engineer each tile into a precise CAD model, which in turn, is exported to a CAM system for the manufacture of the heat protection tile. Scanning is performed while other activities are going on in the shuttle processing facility. Many technicians work simultaneously on the space shuttle structure, which results in structural movements and vibrations. This paper will cover a portable, ultra-fast data acquisition approach used to scan surfaces in this unstable environment.

Wilson, Brad↗

NASA NTRS2008

Revitalizing the Space Shuttle's Thermal Protection System with Reverse Engineering and 3D Vision Technology

Wilson, Brad↗

NASA NTRS1983

Electron velocity distributions near the earth's bow shock

New information is presented on the general characteristics of electron distribution functions upstream, within, and downstream of the earth's bow shock, thereby providing new insights into the instabilities in collisionless shocks. The results presented are from a survey of electron velocity distributions measured near the earth's bow shock between October 1977 and December 1978 using the Los Alamos/Garching plasma instrumentation aboard ISEE 2. A wide variety of distribution shapes is found within the different plasma regions in close proximity to the bow shock. It is found that these shapes can be classified into general types that are characteristic of three different plasma regions, namely the upstream region or electron foreshock, the shock proper where most of the heating occurs, and the downstream region or the magnetosheath. Evidence is provided that field-aligned, rather than cross-field, instabilities are the major source of electron dissipation in the earth's bow shock.

Feldman, W. C.↗

NASA NTRS2017

Rotational Spectral Unmixing of Exoplanets: Degeneracies Between Surface Colors and Geography

Unmixing the disk-integrated spectra of exoplanets provides hints about heterogeneous surfaces that we cannot directly resolve in the foreseeable future. It is particularly important for terrestrial planets with diverse surface compositions like Earth. Although previous work on unmixing the spectra of Earth from disk-integrated multi-band light curves appeared successful, we point out a mathematical degeneracy between the surface colors and their spatial distributions. Nevertheless, useful constraints on the spectral shape of individual surface types may be obtained from the premise that albedo is everywhere between 0 and 1. We demonstrate the degeneracy and the possible constraints using both mock data based on a toy model of Earth, as well as real observations of Earth. Despite the severe degeneracy, we are still able to recover an approximate albedo spectrum for an ocean. In general, we find that surfaces are easier to identify when they cover a large fraction of the planet and when their spectra approach zero or unity in certain bands.

Fujii, Yuka↗

NASA NTRSDate not supplied

Laser Forming of Sheet Metal for In-Space Manufacturing Applications

As the in-space economy matures, the migration of typically Earth-bound manufacturing methods, such as metal forming and joining, up to space will be required to meet the increasing demand for refueling and supply depots, habitats, laboratories, lunar surface structures, and sites for deep-space exploration shipbuilding. Only in this way can the magnitude of individual structures begin to exceed what can be launched, deployed, docked, or inflated and allow true economies of scale to be unlocked in space. However, typical terrestrial methods of forming and shaping sheet metal require massive machinery with the ability to deflect reaction forces to a large mass in a fixed reference frame (Earth). To both limit up-mass required for manufacture and to mitigate the issues of reaction forces in the relative reference frames of space, a non-contact, laser-based method of forming metal sheet is proposed. NASA Marshall Space Flight Center (MSFC), in cooperation with DARPA and the University of Florida (UF), have begun investigation of non-contact methods of laser forming sheet metal in thermal vacuum (TVAC) conditions to great success. To date, several grades of aluminum, stainless steel, and titanium coupons have been formed via laser-induced internal stresses in these metals at both ambient atmosphere and vacuum conditions. Temperatures in these tests ranged from -120 to 60 C, and though the total energy required to induce strain does vary with workpiece temperature and environmental pressure, the method remains predictable and controllable for the materials investigated. It is believed that this method will revolutionize manufacturing in-space as it not only continues to build upon the capabilities of the laser (sensing, marking, cutting, drilling, joining, and now forming) as an all-in-one tool, but also reduces the need to counteract forming forces as would be required in mechanical bending. In theory, all required stress to induce bending is generated through thermal gradient and strain within the workpiece, meaning that the need for reaction control and fuel expense on-orbit will be limited. Archimedes once stated, “Give me a lever long enough and a fulcrum on which to place it, and I shall move the world”. With a laser as our lever and our workpiece its own fulcrum, we can move the world’s manufacturing into space.

Laser↗

NASA NTRS1999

A Study of Short-Term Variations in Jupiter's Synchrotron Emission

Earth-based observations of the flux density and polarization of Jupiter's microwave emission provide useful data to test and constrain computational models of synchrotron radio emission from the inner regions of the Jovian magnetosphere. Stimulated by the sudden brightening of the synchrotron emission caused by the impacts of comet Shoemaker-Levy 9 in 1994, the observational techniques of the NASA-JPL Jupiter Patrol were modified to search for other short-term variations unrelated to the SL-9 event. The characteristics of the improved data base are described and the results of the search for variability on timescales of 5 to 100 days are reported. The first results of Jupiter observations from the Goldstone-Apple Valley Radio Telescope (GAVRT) project are reported and included in the data base. GAVRT is a new project in science education that engages middle- and high school students in science research. The paper also includes new observations of Jupiter's rotational beamed emission, commonly known as the "beaming curve", that describes the observed flux density as a function of System III longitude. The shape of the "beaming curve" is known to change with the parameter D(sub E), the declination of the earth relative to Jupiter's rotational equator. While the history of Jupiter's beaming curve exhibits remarkable stability and repeatability as a function of D(sub E), there may be evidence for short term departures from the nominal curves. Data supporting this tentative conclusion are presented. Preliminary results of a study comparing the observations and computer simulations of the synchrotron beaming curve will also be presented and discussed (see companion paper, "Modeling Jupiter's Synchrotron Emission", by Bolton et. al.). The research reported in this paper was performed by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

Klein, M.J.↗

NASA NTRS1998

The Kepler Mission: A Photometric Search for Earthlike Planets

If Earth lies in or near the orbital plane of an extrasolar planet, that planet passes in front of the disk of its star once each orbit as viewed from Earth. Precise photometry can reveal such transits, which can be distinguished from rotationally-modulated starspots and intrinsic stellar variability by their periodicity, square-well shapes and relative spectral neutrality. Transit observations would provide the size and orbital period of the detected planet. Although geometrical considerations limit the fraction of planets detectable by this technique, many stars can be surveyed within the field of view of one telescope, so transit photometry is quite efficient. Scintillation in and variability of Earth's atmosphere limit photometric precision to roughly one-thousandth of a magnitude, allowing detection of transits by Jupiter-sized planets but not by Earth-sized planets from the ground. The COROT spacecraft will be able to detect Uranus-sized planets orbiting near stars. The Kepler Mission, which is being proposed to NASA's Discovery Program this year, will have a photometer with a larger aperture (1 meter) than will COROT, so it will be able to detect transits by planets as small as Earth. Moreover, the Kepler mission will examine the same star field for four years, allowing confirmation of planets with orbital periods of a year. If the Sun's planetary system is typical for single stars, Kepler should detect approximately 480 terrestrial planets. Assuming the statistics from radial velocity surveys are typical, Kepler should also detect transits of 150 inner giant planets and reflected light variations of 1400 giant planets with orbital periods of less than one week.

Lissauer, Jack J.↗

NASA NTRS1995

A Science Strategy for Space Physics

This report by the Committee on Solar and Space Physics and the Committee on Solar-Terrestrial Research recommends the major directions for scientific research in space physics for the coming decade. As a field of science, space physics has passed through the stage of simply looking to see what is out beyond Earth's atmosphere. It has become a 'hard' science, focusing on understanding the fundamental interactions between charged particles, electromagnetic fields, and gases in the natural laboratory consisting of the galaxy, the Sun, the heliosphere, and planetary magnetospheres, ionospheres, and upper atmospheres. The motivation for space physics research goes far beyond basic physics and intellectual curiosity, however, because long-term variations in the brightness of the Sun virtually affect the habitability of the Earth, while sudden rearrangements of magnetic fields above the solar surface can have profound effects on the delicate balance of the forces that shape our environment in space and on the human technology that is sensitive to that balance. The several subfields of space physics share the following objectives: to understand the fundamental laws or processes of nature as they apply to space plasmas and rarefied gases both on the microscale and in the larger complex systems that constitute the domain of space physics; to understand the links between changes in the Sun and the resulting effects at the Earth, with the eventual goal of predicting the significant effects on the terrestrial environment; and to continue the exploration and description of the plasmas and rarefied gases in the solar system.

Source record↗

NASA NTRS2010

High-Precision Shape Control of In-Space Deployable Large Membrane/Thin-Shell Reflectors

This innovation has been developed to improve the resolutions of future spacebased active and passive microwave antennas for earth-science remote sensing missions by maintaining surface figure precisions of large membrane/thin-shell reflectors during orbiting. The intention is for these sensing instruments to be deployable at orbit altitudes one or two orders of magnitude higher than Low Earth Orbit (LEO), but still being able to acquire measurements at spatial resolution and sensitivity similar to those of LEO. Because active and passive microwave remote sensors are able to penetrate through clouds to acquire vertical profile measurements of geophysical parameters, it is desirable to elevate them to the higher orbits to obtain orbital geometries that offer large spatial coverage and more frequent observations. This capability is essential for monitoring and for detailed understanding of the life cycles of natural hazards, such as hurricanes, tropical storms, flash floods, and tsunamis. Major components of this high-precision antenna-surface-control system include a membrane/thin shell reflector, a metrology sensor, a controller, actuators, and corresponding power amplifier and signal conditioning electronics (see figure). Actuators are attached to the back of the reflector to produce contraction/ expansion forces to adjust the shape of the thin-material reflector. The wavefront-sensing metrology system continuously measures the surface figure of the reflector, converts the surface figure to digital data and feeds the data to the controller. The controller determines the control parameters and generates commands to the actuator system. The flexible, piezoelectric polymer actuators are thus activated, providing the control forces needed to correct any distortions that exist in the reflector surface. Piezoelectric polymer actuators are very thin and flexible. They can be implemented on the back of the membrane/thin-shell reflector without introducing significant amounts of mass or stiffness to the reflector. They can be rolled up or folded to accommodate the packaging needed for launch. An analytical model of the system, which includes the membrane reflector, actuator, and controller has been developed to investigate the functionality of this control system on a 35-meter-diameter membrane reflector. The performance of this system under external disturbances such as in space thermal loads and W-error due to inflation has been investigated. A subscale breadboard has been developed, and the functionality of this control concept has been demonstrated by this breadboard.

Watkins, Ronald↗

NASA NTRS1983

The electronic switching spherical array antenna for the Earth Radiation Budget Spacecraft

The ESSA is a microprocessor-controlled antenna for low orbiting spacecraft for telemetry and command relay through the Tracking and Data Relay Satellite System (TDRSS). The array is a hemispherical shape covered with disk radiating elements. A group of radiating elements are continuously selected by the microprocessor controller to form a beam in the direction of a TDRS. A radial switching power divider uses PIN diodes to select the desired radiating elements. The antenna gain is a function of the size of the hemispherical dome. A 30-inch diameter dome is presently being built for the Earth Radiation Budget Spacecraft (ERBS). Gain of this antenna over a hemisphere is 14 dBi and polarization is lefthand circular. There are 145 radiating elements with 12 being used at one time to form a beam. The ESSA subsystem weights 74 pounds and power consumption is 20 watts. RF power handling capability is 30 watts. The S-Band radiating elements have a 10 percent bandwidth that allows simultaneous transmission and reception.

Kudrna, K.↗

NASA NTRS1983

The detection of X rays from Jupiter

X rays in the energy band 0.2-3.0 keV have been detected coming from both polar regions of Jupiter. The observations were made in 1979 and 1981 by using the imaging proportional counter and high resolution imaging detectors on the Einstein X-ray astronomy satellite. The measured flux density of approximately 0.0006/sq cm-sec at earth corresponds to an X ray luminosity of approximately 4 x 10 to the 9th W in the 0.2- to 3.0-keV energy band. The energy spectrum of the X rays is extremely soft and can be characterized by a power law with an exponent of approximately 2.3. Detector energy resolution is insufficient to distinguish a soft line spectrum from a continuum. However, the shape of the response and the observed X ray power indicate that the source of this auroral emission is not electron bremsstrahlung as on the earth, but is most probably line emission from O and S ions with energies between 0.03 and 4.0 MeV/nucleon precipitating from the outer boundary of the Io plasma torus at L approximately 8.

Metzger, A. E.↗

DOE OSTI2024

The Arctic

Arctic observations in 2023 provided clear evidence of rapid and pronounced climate and environmental change, shaped by past and ongoing human activities that release greenhouse gases into the atmosphere and push the broader Earth system into uncharted territory. This chapter provides a snapshot of 2023 and summarizes decades-long trends observed across the Arctic, including warming surface air and sea-surface temperatures, decreasing snow cover, diminishing sea ice, thawing permafrost, and continued mass loss from the Greenland Ice Sheet and Arctic glaciers. These changes are driving a transition to a wetter, greener, and less frozen Arctic, with serious implications for Arctic peoples and ecosystems, as well as for low- and midlatitudes

54 ENVIRONMENTAL SCIENCES↗

NASA NTRS1973

Proton scattering in the region near the earth's bow shock.

Lockheed spectrometer data from orbits 1 through 20 of Ogo 5 are used to study proton scattering near the bow shock. Correlative UCLA fluxgate magnetometer data from the satellite are used to complete motion studies of the bow shock when spectrometer data are missing. Thirty-eight analyzable sets of multiple shock crossings show 358 shock encounters ranging from 10 to 22 earth radii and spanning sun-earth-satellite angles from 30 to 90 deg. Gross features of the study show that the location and shape of the bow shock are in good agreement with the hydrodynamic model of the bow shock.

Ossakow, S. L.↗

NASA NTRS1992

Analysis of a generalized dual reflector antenna system using physical optics

Reflector antennas are widely used in communication satellite systems because they provide high gain at low cost. Offset-fed single paraboloids and dual reflector offset Cassegrain and Gregorian antennas with multiple focal region feeds provide a simple, blockage-free means of forming multiple, shaped, and isolated beams with low sidelobes. Such antennas are applicable to communications satellite frequency reuse systems and earth stations requiring access to several satellites. While the single offset paraboloid has been the most extensively used configuration for the satellite multiple-beam antenna, the trend toward large apertures requiring minimum scanned beam degradation over the field of view 18 degrees for full earth coverage from geostationary orbit may lead to impractically long focal length and large feed arrays. Dual reflector antennas offer packaging advantages and more degrees of design freedom to improve beam scanning and cross-polarization properties. The Cassegrain and Gregorian antennas are the most commonly used dual reflector antennas. A computer program for calculating the secondary pattern and directivity of a generalized dual reflector antenna system was developed and implemented at LeRC. The theoretical foundation for this program is based on the use of physical optics methodology for describing the induced currents on the sub-reflector and main reflector. The resulting induced currents on the main reflector are integrated to obtain the antenna far-zone electric fields. The computer program is verified with other physical optics programs and with measured antenna patterns. The comparison shows good agreement in far-field sidelobe reproduction and directivity.

Acosta, Roberto J.↗

NASA NTRS1992

Asteroid 951 Gaspra - Pre-Galileo physical model

An effort is made to derive from Galileo's 1991 encounter of the S-type asteroid 951 Gaspra general lessons that will be applicable to prospective earth-based observations of other asteroids. Attention is accordingly given to the derivation of spin-vector and shape parameters en route to more detailed physical characterization of a given asteroid. A future encounter of Gaspra by Galileo will be required to verify the present model.

Magnusson, P.↗

NASA NTRS1998

Discovery of the 198 Second X-Ray Pulsar GRO J2058+42

GRO J2058+42, a transient 198 s X-ray pulsar, was discovered by the Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray Observatory (CGRO) during a "giant" outburst in 1995 September-October. The total flux peaked at about 300 mcrab (20-50 keV) as measured by Earth occultation. The pulse period decreased from 198 to 196 s during the 46 day outburst. The pulse shape evolved over the course of the outburst and exhibited energy-dependent variations. BATSE observed five additional weak outbursts from GRO J2058 + 42, each with a 2 week duration and a peak-pulsed flux of about 15 mcrab (20-50 keV), that were spaced by about 110 days. An observation of the 1996 November outburst by the Rossi X-Ray Timing Explorer (RXTE) proportional counter array (PCA) localized the source to within a 4 s radius error circle (90% confidence) centered on R.A. = 20h 59m.0, decl. = 41 deg 43 s (J2000). Additional shorter outbursts with peak-pulsed fluxes of about 8 mcrab were detected by BATSE halfway between the first four 15 mcrab outbursts. The RXTE All-Sky Monitor detected all eight weak outbursts with approximately equal durations and intensities. GRO J2058 + 42 is most likely a Be/X-ray binary that appears to outburst at periastron and apastron, No optical counterpart has been identified to date, and no X-ray source was present in the error circle in archival ROSAT observations.

Wilson, Colleen A.↗

NASA NTRS2006

Terrestrial Water Mass Load Changes from Gravity Recovery and Climate Experiment (GRACE)

Recent studies show that data from the Gravity Recovery and Climate Experiment (GRACE) is promising for basin- to global-scale water cycle research. This study provides varied assessments of errors associated with GRACE water storage estimates. Thirteen monthly GRACE gravity solutions from August 2002 to December 2004 are examined, along with synthesized GRACE gravity fields for the same period that incorporate simulated errors. The synthetic GRACE fields are calculated using numerical climate models and GRACE internal error estimates. We consider the influence of measurement noise, spatial leakage error, and atmospheric and ocean dealiasing (AOD) model error as the major contributors to the error budget. Leakage error arises from the limited range of GRACE spherical harmonics not corrupted by noise. AOD model error is due to imperfect correction for atmosphere and ocean mass redistribution applied during GRACE processing. Four methods of forming water storage estimates from GRACE spherical harmonics (four different basin filters) are applied to both GRACE and synthetic data. Two basin filters use Gaussian smoothing, and the other two are dynamic basin filters which use knowledge of geographical locations where water storage variations are expected. Global maps of measurement noise, leakage error, and AOD model errors are estimated for each basin filter. Dynamic basin filters yield the smallest errors and highest signal-to-noise ratio. Within 12 selected basins, GRACE and synthetic data show similar amplitudes of water storage change. Using 53 river basins, covering most of Earth's land surface excluding Antarctica and Greenland, we document how error changes with basin size, latitude, and shape. Leakage error is most affected by basin size and latitude, and AOD model error is most dependent on basin latitude.

Seo, K.-W.↗