Search NASA⌕ Search

SEARCH · Search NASA

Results for “Explore Earth”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

The development of performance, interference, sharing and coordination criteria

The criteria for sharing and coordination between the Earth Exploration Satellite service and other radio services is not fully developed at this time. The purpose is to develop a plan showing how the necessary criteria might be developed. Some criteria does exist in the form of general restrictions, protection criteria, and coordination procedures for space and terrestrial services sharing the same bands. Determining suitable criteria for EES bands depends on the use of the band and the shared services. For example the criteria developed for EES passive sensing band will be developed in a manner different than for a telemetry band. In either case the resultant criteria will be related to, and can be referenced from the system noise power or equivalent noise temperature.

Tillotson, Tom↗
NASA NTRS1987

Leadership and America's future in space

In response to growing concern over the posture and long-term direction of the U.S. civilian space program, a task group was formed to define potential U.S. space initiatives, and to evaluate them in light of the current space program and the nation's desire to regain and retain space leadership. The objectives were to energize a discussion of the long-term goals of the civilian space program and to begin to investigate overall strategies to direct that program to a position of leadership. Four initiatives were identified: mission to planet Earth; exploration of the solar system; outpost on the Moon, and humans to Mars. All four initiatives were developed in detail, and the implications and requirements of each was assessed. The long-term goals, current posturing required to attain these goals, and the need for a continuing process to define, refine, and assess both the goals and the strategy to achieve them are discussed.

Sally K Ride↗
NASA NTRS1988

Teaching old spacecraft new tricks

The technique of sending existing space probes on extended mission by altering their orbital paths with gravity-assist maneuvers and relatively brief rocket firings is examined. The use of the technique to convert the International Sun-Earth Explorer 3 mission into the International Cometary Explorer mission is discussed. Other examples are considered, including the extension of the Giotto mission and the retargeting of the Sakigake spacecraft. The original and altered trajectories of these three missions are illustrated.

Farquhar, Robert↗
NASA NTRS1990

Solar emission levels at low radio frequencies

Solar radio emission could seriously interfere with observations made by a low frequency (1 to 10 MHz) array in space. International Sun-Earth Explorer (ISEE-3) radio data were used to determine solar emission level. The results indicate that solar emission should seriously disturb less than ten percent of the data, even during the years of solar maximum. Thus it appears that solar emission should not cause a disastrous loss of data. The information needed to design procedures to excise solar interference from the data produced by any low-frequency array is provided.

Erickson, W. C.↗
NASA NTRS1991

Studies of magnetopause structure

From the International Sun-Earth Explorers (ISEE) 1 magnetopause crossings on November 10, 1977, three-dimensional distribution functions for energetic ions were studied in the magnetosphere, through the magnetopause, and in the magnetosheath (Speiser and Williams, 1982). The particle distributions were particularly examined at and near the times that Russell and Elphic (1978) identified as flux transfer events (FTE). Using a simple, one-dimensional, quasi-static model, particle orbits were followed numerically, from the magnetosphere into the sheath. The inner, trapped, distribution initializes the distribution function. Liouville's theorem allows the inner distribution to be mapped into the sheath following the orbits. This mapping is shown for four mangetosheath ion flows (MIF's) corresponding to four flux transfer events. Results from the studies are discussed. A brief discussion of current sheet particle motion is presented.

Speiser, Theodore W.↗
NASA NTRS1989

ISEE/ICE plasma wave data analysis

The work performed for the period 1 Jan. 1985 to 30 Oct. 1989 is presented. The objective was to provide reduction and analysis of data from a scientific instrument designed to study solar wind and plasma wave phenomena on the International Sun Earth Explorer 3 (ISEE-3)/International Cometary Explorer (ICE) missions.

Greenstadt, E. W.↗
NASA NTRS1992

The ITU as a means of facilitating international collaboration on space radiocommunication systems

The role of the International Telecommunication Union (ITU) in the international collaboration in the field of space radio communications is reviewed. The history of the ITU, its structure and activities, and the functions of the permanent organs of the ITU are briefly discussed. Attention is then given to new space service applications for communications around 400 MHz, space services near 2 GHz, new space service applications above 20 GHz, and links for future planetary missions. The discussion also covers deep space allocations near 32/34 GHz, space VLBI applications, new earth exploration satellite service applications, and future work.

Kimball, H.↗
NASA NTRS1991

Measurements of the spatial structure and directivity of 100 KeV photon sources in solar flares using PVO and ISEE-3 spacecraft

The objective of this grant was to measure the spatial structure and directivity of the hard X-ray and low energy gamma-ray (100 keV-2 MeV) continuum sources in solar flares using stereoscopic observations made with spectrometers aboard the Pioneer Venus Orbiter (PVO) and Third International Sun Earth Explorer (ISEE-3) spacecraft. Since the hard X-ray emission is produced by energetic electrons through the bremsstrahlung process, the observed directivity can be directly related to the 'beaming' of electrons accelerated during the flare as they propagate from the acceleration region in the corona to the chromosphere/transition region. Some models (e.g., the thick-target model) predict that most of the impulsive hard X-ray/low energy gamma-ray source is located in the chromosphere, the effective height of the X-ray source above the photosphere increasing with the decrease in the photon energy. This can be verified by determining the height-dependence of the photon source through stereoscopic observations of those flares which are partially occulted from the view of one of the two spacecraft. Thus predictions about beaming of electrons as well as their spatial distributions could be tested through the analysis proposed under this grant.

Anderson, Kinsey A.↗
NASA NTRS1994

Flank solar wind interaction

In this report we will summarize the results of the work performed under the 'Flank Solar Wind Interaction' investigation in support of NASA's Space Physics Guest Investigator Program. While this investigation was focused on the interaction of the Earth's magnetosphere with the solar wind as observed by instruments on the International Sun-Earth Explorer (ISEE) 3 spacecraft, it also represents the culmination of decades of research performed by scientists at TRW on the rich phenomenology of collisionless shocks in space.

Moses, Stewart L.↗
NASA NTRS1994

Imaging the effect of dipole tilt on magetotail boundaries

Eight years of Interplanetary Monitoring Platform (IMP) 8, four years of International Sun Earth Explorer (ISEE) 2, and one year of IMP 7 magnetometer data have been combined to produce an 'image' of the average magnetic field for a YZ cross section (aberrated GSM) of the magnetotail at a downtail distance of 25 R(sub E). The shape of the neutral sheet and magnetopause boundaries can be observed directly from the images. A fitting function that qualitatively matches the observed boundary shape can then be chosen. This approach improves on previous fits to possible unsuitable functional forms specified independently of the data. In addition, as a refinement of previous studies, we have corrected for varying solar wind dynamic pressure and the effects of tail flaring. We find the magnetopause is displaced above the XY plane with increasing dipole tilt. The neutral sheet is found to curve slightly more than the model of Fairlfield (1980) during times of large dipole tilt and near the flanks appears to differ substantially from the neutral sheet shape given by the analytic model of Voigt (1984), the more recent neutral sheet model of Dandouras (1988) based on the Voigt model, and the semi-empirical model of Tsyganenko (1989).

Hammond, C. Max↗
NASA NTRS1994

Interplanetary magnetic field dependency of stable Sun-aligned polar cap arcs

This is the first analysis, using a statistically significant data set, of the morphological dependence of the presence, orientation, and motion of stable sun-aligned polar cap arcs upon the vector interplanetary magnetic field (IMF). For the one winter season analyzed we had 1392 all-sky 630.0-nm images of 2-min resolution containing a total of 150 polar cap arcs, all with corresponding values of the IMF as measured by International Monitoring Platform (IMP) 8 or International Sun Earth Explorer (ISEE) 2. After demonstrating an unbiased data set with smooth normal distributions of events versus the dimensions of time, space, and IMF component, we examine IMF dependencies of the properties of the optical arcs. A well-defined dependence for B(sub z) is found for the presence/absence of stable Sun-aligned polar cap arcs. Consistent with previous statistical studies, the probability of observing polar cap aurora steadily increases for larger positive values of B(sub z), and linearly decreases when B(sub z) becomes more negative. The probability of observing Sun-aligned arcs within the polar cap is determined to vary sharply as a function of the arc location; arcs were observed 40% of the time on the dawnside and only 10% on the duskside. This implies an overall probability of at least 40% for the whole polar cap. 20% of the arcs were observed during 'southward IMF conditions,' but in fact under closer inspection were found to have been formed under northward IMF conditions; these 'residual' positive B(sub z) arcs ha d a delayed residence time in the polar cap of about what would be expected after a north to south transition of B(sub z). A firm dependence on B(sub y) is also found for both the orientation and the dawn-dusk direction of motion of the arcs. All the arcs are Sun-aligned to a first approximation, but present deviations from this orientation, depending primarily upon the location of the arc in corrected geomagnetic (CG) coordinates. The arcs populating the 06-12 and the 12-18 quadrants of the CG coordinate system point toward the cusp. The B(sub y) dependency of the arc alignment is consistent with a cusp displacement in local time according to the sign of B(sub y). We found that the arc direction of motion depended both on B(sub y) and the arc location within the polar cap. For a given value of B(sub y) two well-defined regions (or cells) exist. Within each cell the arcs move in the same direction toward the boundary between the cells. The arcs located in the duskside move dawnward; those in the dawnside move duskward. The relative size of these dusk and dawn regions (or cells) are controlled by the magnitude of B(sub y). This persistent dusk-dawn motion fo the polar cap arcs is interpreted in terms of newly open flux tubes entering the polar cap and exerting a displacement of the convective cells and the polar cap arcs that are embedded within them.

Valladares, C. E.↗
NASA NTRS1994

Double vision: Remote sensing of a flux transfer event with ISEE 1 and 2

A flux transfer event recorded by the International Sun-Earth Explorers (ISEE) 1 and 2 spacecraft in the northern hemisphere near local noon is examined using analysis techniques developed recently for determination from single satellite magnetometer data of the orientation and cross-sectional shape of a two-dimensional disturbance moving along the magnetopause. The analysis is performed independently on the magnetic field data recorded by each satellite, enabling us to check the consistency of the results and thus to benchmark the method. The analysis is also extended to utilize the dual magnetometer measurements for determination of the event speed and size (which for a single spacecraft requires use of three-dimensional plasma velocity data to obtain a deHoffmann-Teller frame velocity) and for accommodating acceleration of the magnetopause normal to itself, which results in a curved spacecraft trajectory in the frame of reference moving with the disturbance. The analysis of the disturbance reveals that while its overall size is about 34,000 km in a direction parallel to the magnetopause but perpendicular to the event axis, the actual size of the bulge causing the field disturbance may have been as small as 9000 km with a dimension perpendicular to the magnetopause of the order of 1200 km. The bulge is found to be traveling at a speed of about 140 km/s toward the northern dawn quadrant of the dayside magnetopause. While plasma data from ISEE 2 provides evidence of plasma jetting, which suggests the event may be associated with reconnection, the orientation of the flux tube axis obtained from analysis is significantly different from the expected reconnection line direction. A discussion of possible interpretations of this bulge orientation and motion is provided.

Walthour, D. W.↗
NASA NTRS1994

Statistical study of ULF wave occurrence in the dayside magnetosphere

Ultralow-frequency (ULF) waves are observed almost everywhere in the dayside magnetosphere. The mechanism by which these waves are generated and transformed in the dayside magnetosphere is still not understood. Here we report a statistical study of these waves based on magnetic field data from the International Sun-Earth Explorer 1 (ISEE 1) spacecraft. Data from the first traversal of the spacecraft through the entire dayside magnetosphere have been examined to determine the spatial distribution of wave occurrence. Successive 20-min segments of data were transformed to a field-aligned coordinate system. The parallel component was detrended and all three components of the field spectrally analyzed. Wave occurrence was defined by the presence of significant peaks in the power spectra. Wave events were categorized by three wave frequency bands: Pc 3 with T approximately 10-45 s; Pc 4 with T approximately 45-150 s; the short-period part of the Pc 5 wave band with T approximately 150-324 s. Properties of the spectral peaks were then entered into a data base. The data base was next sorted to determine the spatial occurrence pattern for the waves. Our results show that Pc 3 waves most frequently occur just outside synchronous orbit and are approximately centered on local noon. Pc 4 waves have a similar distribution with its peak further out. Pc 5 waves have high occurrence rate at the two flanks of the magnetosphere. Peaks in spectra obtained near the magnetopause are less clearly defined than those deeper in the magnetosphere.

Cao, M.↗
NASA NTRS1994

Energetic-particle abundances in impulsive solar flare events

We report on the abundances of energetic particles from impulsive solar flares, including those from a survey of 228 He-3 rich events, with He-3/He-4 is greater than 0.1, observed by the International Sun Earth Explorer (ISEE) 3 spacecraft from 1978 August through 1991 April. The rate of occurrence of these events corresponds to approximately 1000 events/yr on the solar disk at solar maximum. Thus the resonant plasma processes that enhance He-3 and heavy elements are a common occurrence in impulsive solar flares. To supply the observed fluence of He-3 in large events, the acceleration must be highly efficient and the source region must be relatively deep in the atmosphere at a density of more than 10(exp 10) atoms/cu cm. He-3/He-4 may decrease in very large impulsive events because of depletion of He-3 in the source region. The event-to-event variations in He-3/He-4, H/He-4, e/p, and Fe/C are uncorrelated in our event sample. Abundances of the elements show a pattern in which, relative to coronal composition, He-4, C, N, and O have normal abundance ratios, while Ne, Mg, and Si are enhanced by a factor approximately 2.5 and Fe by a factor approximately 7. This pattern suggests that elements are accelerated from a region of the corona with an electron temperature of approximately 3-5 MK, where elements in the first group are fully ionized (Q/A = 0.5), those in the second group have two orbital electrons (Q/A approximately 0.43), and Fe has Q/A approximately 0.28. Ions with the same gyrofrequency absorb waves of that frequency and are similarly accelerated and enhanced. Further stripping may occur after acceleration as the ions begin to interact with the streaming electrons that generated the plasma waves.

Reames, D. V.↗
NASA NTRS1994

Dynamics and efficiency of type III solar radio emission

Existing calculations of nonlinear coupling coefficients for fundamental and harmonic emission via three-wave interactions are refined and used to calculate the conversion efficiency of Langmuir energy into electromagnetic waves when the Langmuir waves have the observed bursty form. Resulting field strengths for harmonic emission are found to be consistent with typical International Sun Earth Explorer 3 (ISSE 3) observations at 1 AU. Fundamental emission at 1 AU is found to proceed only when stimulated by the presence of a source of ion sound waves. However, it is argued that electrostatic decay of Langmuir waves can supply the necessary waves provided the driving electron beam is sufficiently fast. Under these conditions, the predicted fundamental field strengths can account for both the highest and typical fields observed; they also dominate the predicted harmonic fields, consistent with observations. This mechanism is also consistent with previous observations that fundamental emission generally occurs early in type III events, when the beam is fastest. For typical parameters it is shown that neither fundamental nor harmonic emission saturates its respective source instability, contrary to previous assumptions. However, saturation cannot be ruled out under particularly favorable conditions.

Robinson, P. A.↗
NASA NTRS1994

A proposed neutral line signature

An identifying signature is proposed for the existence and location of the neutral line in the magnetotail. The signature, abrupt density and temperature changes in the Earth-tail direction, was first discovered in test particle simulations. Such temperature variations have been observed in International Sun Earth Explorer (ISEE) data (Huang et al., 1992), but their connection to the possible existence of a neutral line in the tail has not yet been established. The proposed signature develops earlier than the ion velocity space ridge of Martin and Speiser (1988) but can only be seen by spacecraft in the vicinity of the neutral line, while the latter can locate a neutral line remotely.

Doxas, I.↗
NASA NTRS1994

A test of source-surface model predictions of heliospheric current sheet inclination

The orientation of the heliospheric current sheet predicted from a source surface model is compared with the orientation determined from minimum-variance analysis of International Sun-Earth Explorer (ISEE) 3 magnetic field data at 1 AU near solar maximum. Of the 37 cases analyzed, 28 have minimum variance normals that lie orthogonal to the predicted Parker spiral direction. For these cases, the correlation coefficient between the predicted and measured inclinations is 0.6. However, for the subset of 14 cases for which transient signatures (either interplanetary shocks or bidirectional electrons) are absent, the agreement in inclinations improves dramatically, with a correlation coefficient of 0.96. These results validate not only the use of the source surface model as a predictor but also the previously questioned usefulness of minimum variance analysis across complex sector boundaries. In addition, the results imply that interplanetary dynamics have little effect on current sheet inclination at 1 AU. The dependence of the correlation on transient occurrence suggests that the leading edge of a coronal mass ejection (CME), where transient signatures are detected, disrupts the heliospheric current sheet but that the sheet re-forms between the trailing legs of the CME. In this way the global structure of the heliosphere, reflected both in the source surface maps and in the interplanetary sector structure, can be maintained even when the CME occurrence rate is high.

Burton, M. E.↗
NASA NTRS1994

A statistical survey of the central plasma sheet

We present a statistical analysis of the ion plasma properties and magnetic field of the central plasma sheet at distances from 10 to 23 R(sub E) from the Earth. This study incorporates International Sun-Earth Explorer (ISEE) 1 plasma sheet samples accumulated with the University of Iowa Lepedea plasma analyzer during 1979. Our study of the bulk properties of the ion plasma shows that there is relatively little change as a result of increasing geomagnetic activity. The main macroscopic effect is an increase in plasma temperature. When the transverse profile of the plasma sheet is examined, it is clear that this increase in temperature occurs preferentially at high latitudes. The magnetic field shows an increase in magnitude in the vicinity of the neutral sheet periods of high geomagnetic activity. The radial profiles of the density, temperature, plasma, and magnetic pressures show a gradient in total energy density in the plasma sheet. The convective velocities are systematically directed earthward, and there is a bias toward positive V(sub y) on the duskside of the magnetotail. We infer that particle motion can be attributed to a pressure gradient, combined with steady state convective electric fields. We compute the convective electric fields from our measured bulk velocities, arriving at a pattern similar to that observed at low altitudes. The cross-tail electric field E(sub y) is dominant near the neutral sheet region, but at high latitudes E(sub z) is a major component. Our results suggest that the plasma sheet boundary layer, rather than the central plasma sheet, is a region of diverging electric fields. The picture of the plasma sheet that emerges from our study is that of a stable reservoir of hot plasma in which thermodynamic, rather than dynamic, processes is important.

Huang, C. Y.↗