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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Solar wind variations and geomagnetic storms - A study of individual storms based on high time resolution ISEE 3 data

Two independent methods are employed to determine the relationship between the parameter epsilon and total energy dissipation rate of the magnetosphere U sub T by selecting disturbed periods from the same data d set used by Baker et al. (1983). Specifically, four storms are examined in detail, since the accuracy of estimating U sub T is significantly improved during disturbed periods. The first method assumes that U sub T = M sub A exp.2- alpha(epsilon) where M sub A is the Alfven Mach number and alpha varies with time. The second method considers a linear, time-invariant dynamic system with epsilon as input and U sub T as output. This means that U sub T = W(asterisk)epsilon where asterisk is the convolution and W is a transfer function characteristic of the system. It is found that alpha values fluctuate mainly between 0 and -0.25. The transfer function analysis indicates that W often resembles a delta-function or a narrow rectangular impulse. Both results give the same implication (namely that U sub T is approximately equal to epsilon) and thus are consistent with the view that the magnetosphere is primarily a directly driven system during disturbed periods.

Akasofu, S.-I.↗
NASA NTRS1985

Particles upstream of the pre-dawn bow shock - ISEE-3 observations

The first observations of energetic ions (equal to or greater than 30 keV) in the region upstream of the pre-dawn bow shock (X between 0 and -60 Re inclusively) are presented. The intensity in this region is controlled by the direction of the interplanetary magnetic field (IMF) and is maximized when the IMF is around the spiral direction. The particle distributions are highly anisotropic with the anisotropy directed perpendicular to the magnetic field. In the E x B frame this perpendicular anisotropy is conserved and it is argued that the distribution is pancake-like. This indicates that the energetic particles in the pre-dawn upstream region have their origin in the near-earth upstream region, from where they are convected by the solar wind perpendicular to the magnetic field. It is therefore concluded that acceleration occurs mainly near the nose of the bow shock, and particle acceleration at the distant bow shock is weak.

Terasawa, T.↗
NASA NTRS1985

ISEE observations of the magnetopause - Reconnection and the energy balance

The total energy balance for two events with the objective of obtaining check on the interpretation in terms of reconnection is examined. To within experimental uncertainties, the plasma and magnetic field data are consistent with reconnection. An enthalpy increase comparable to the kinetic energy increase occurs in the magnetopause. Thus substantial dissipation is present in the rotational discontinuity. An ion heat flow associated with a beam of reflected magnetosheath particles carried away some 20 percent of the total converted electromagnetic energy.

Paschmann, G.↗
NASA NTRS1986

Comparative ULF foreshocks of earth and Venus observed by ISEE 1 and PVO

The region occupied by the ULF compressional foreshock of a planetary shock depends on the IMF direction. As the cone angle of the IMF, the angle theta -XB between the solar ecliptic coordinate theta-XF X-axis and the field B, increases, the cone angle of the foreshock boundary, the angle theta-XF between the X-axis and the leading envelope of the foreshock, also increases. A statistical examination of the Venus and earth foreshocks shows that the trends of theta-XF of the two foreshocks are parallel, and quite similar under joint solar wind conditions. So are the local field-normal angles and return ion velocities at the bases of the respective foreshocks.

Greenstadt, E. W.↗
NASA NTRS1987

Plasma wave evidence for reflected ions in front of subcritical shocks - ISEE 1 and 2 observations

Plasma wave profiles of bow shock crossings at ion acoustic frequencies exhibit 'feet' or 'pedestals', just as magnetic field profiles do. These ion-acoustic feet, consisting of increases in ion wave amplitude over background, are observed in front of virtually all quasi-perpendicular shocks, regardless of Mach number, but are closely associated with magnetic feet and reflected ions circulating around the ambient upstream field at supercritical shocks. Observed gyroradii of the reflected ions have been found to be commensurate with the thicknesses of the magnetic feet, which consist of increases in average field magnitude just outside the main shock ramps in front of supercritical shocks. Estimated scale lengths (gyroradii) of reflected protons are proportional to the thicknesses of acoustic wave feet in all cases, indicating that such protons are probably universally present at subcritical as well as supercritical shocks, although the protons are observed only sporadically because of instrumental limitations. The mere presence or absence of reflected ions in front of a shock may therefore be an insufficient diagnostic of the shock's status with respect to criticality and ion dissipation.

Greenstadt, E. W.↗
NASA NTRS1989

Analysis of ISEE-3/ICE solar wind data

Under the grant that ended November 11, 1988 work was accomplished in a number of areas, as follows: (1) Analysis of solar wind data; (2) Analysis of Giacobini/Zinner encounter data; (3) Investigation of solar wind and magnetospheric electron velocity distributions; and (4) Experimental investigation of the electronic structure of clusters. Reprints and preprints of publications resulting from this work are included in the appendices.

Coplan, Michael A.↗
NASA NTRS1988

Intercalibration of the hard X-ray spectrometers on the PVO and ICE (ISEE-3) spacecraft

The energetic photon spectrometers aboard the ICE and PVO (Pioneer Venus Orbiter) are described briefly, and the procedure for their in-flight calibrations is discussed. Successful intercalibration of these two instruments led to stereoscopic observations of 100 keV-2 MeV photon sources in solar flares and the study of the directivity and height structure of these sources. The impulsive hard X-ray source is found to extend from the chromosphere to the corona, the brightness of the source decreasing rapidly with increase in height above the chromosphere. The analysis so far indicates no systematic directivity for the hard X-ray source. The observations are consistent with energetic electrons accelerated in the corona propagating downward toward the chromosphere. However, when avaraged over the duration of an impulsive hard X-ray flare, the 'beaming' of electrons is found to be small in most flares.

Kane, S. R.↗
NASA NTRS1990

Description of SAFIRE for ISES

The SAFIRE (Spectroscopy of the Atmosphere using Far Infrared Emission) is a limb emission experiment using a far-IR Fourier transform spectrometer (FTS) and a mid-IR broadband multispectral radiometer covering the range 80 to 1600/cm. The purpose of this experiment is to obtain vertical distributions of temperature and key constituents of O(y), HO(y), NO(y), ClO(y), and BrO(y) families in the stratosphere, mesosphere, and thermosphere. The spectral channels and gases within each channel are summarized. The instrument includes a 48 element (6 x 8) Ge:GA detector array operating at 4 K in the far-IR and a 105 element (7 x 15) HgCdTe array operating at 80 K in the mid-IR. The SAFIRE uses four different scan modes for vertical coverage and resolution to address various scientific requirements. The SAFIRE data reduction will start with the retrieval of temperature profile as a function of pressure using two CO2 channel data. Constituent distributions then are obtained from other channel data using the retrieved temperature profile. The SAFIRE measurements are limited to the region above the tropopause because of radiance saturation by H2O and clouds. The computational capability necessary to process at the instrument data rate is estimated to be 19 MFLOPS for FTS data and 0.02 MFLOPS for radiometer data. It seems, therefore, that the real-time applications of SAFIRE data using an onboard processing device is not feasible. Although a temperature anomaly may be detected from the two CO2 radiometer channels using an onboard processor for the stratosphere, it is not possible to distinguish between CO2 outflux and temperature anomaly. Temperature anomaly does not, therefore, offer tropospheric information useful for real-time application.

Park, Jae H.↗
NASA NTRS1990

Brief state-of-the-art review on optical communications for the NASA ISES workshop

The current state of the art of optical communications is briefly reviewed. This review covers NASA programs, DOD and other government agency programs, commercial aerospace programs, and foreign programs. Included is a brief summary of a recent NASA workshop on optical communications. The basic conclusions from all the program reviews is that optical communications is a technology ready to be accepted but needed to be demonstrated. Probably the most advanced and sophisticated optical communications system is the Laser Intersatellite Transmission Experiment (LITE) system developed for flight on the Advanced Communications Technology Satellite (ACTS). Optical communications technology is available for the applications of data communications at data rates in the under 300 MBits/sec for nearly all applications under 2 times GEO distances. Applications for low-earth orbiter (LEO) to ground will allow data rates in the multi-GBits/sec range. Higher data rates are limited by currently available laser power. Phased array lasers offer technology which should eliminate this problem. The major problem of cloud coverage can probably be eliminated by look ahead pointing, multiple ground stations, and knowledge of weather conditions to control the pointing. Most certainly, optical communications offer a new spectral region to relieve the RF bands and very high data communications rates that will be required in less than 10 years to solve the communications problems on Earth.

Hendricks, Herbert D.↗
NASA NTRS1990

Applications of ISES for geology

The principal applications for onboard data processing and real-time data transmission in the geological sciences are the detection of early warning signs of potential catastrophic events and the rapid assessment of impact and damage following major events. Also, the opportunity for quick look and supporting data during field investigations should not be disregarded. The Eos platforms are ideal for these applications because of the variety of earth sensing instruments and their differing modes of operation. Further study is required to define the role for each instrument and to assess how they can aid each other in establishing an improved output product.

Bowker, David E.↗
NASA NTRS1990

Applications of ISES for the oceans

The need in oceanography for direct broadcast, why, and what type are discussed. Four reasons for support exist: need for real-time observations in support of field studies; need to back up point failures; need for experimentation with onboard processing and selection of data for direct broadcasting; and the need to develop future operational NOAA systems. Each of these areas is examined.

Esaias, W. E.↗
NASA NTRS1990

Applications of ISES for snow, ice, and sea state

There will be six facility instruments on the NASA NPOP-1 and NPOP-2 and additional instruments on the Japanese and European satellites. Also, there are the 24 selected NASA instruments that may be flown on one of the platforms. Many of these instruments can provide data that could be very useful for real-time data studies in the snow and ice area. Any one instrument is not addressed in particular, but emphasis is placed on what is potentially possible using the capabilities of some of these instruments.

Chang, Alfred T. C.↗
NASA NTRS1990

Applications of ISES for instrument science

It is often the case that some instruments being used for geophysical measurements cannot measure some parameters that are important for processing the data obtained using the instrument. However, the parameters of interest may be measured by other instruments and these data made available to the operators of the first instrument. Processing the data immediately after it is acquired is useful in directing the operation of the same or different instrument or in providing a quick look data set to users on the ground. The four applications which are considered are: the decision to acquire data due to some important occurrence detected by Eos instruments; the decision not to acquire data at a scheduled time and/or location; the decision to acquire additional data to improve data quality; and combining data from several sources to enhance data quality. General examples are presented, which may or may not apply directly to Eos instruments on the various platforms.

Grant, William B.↗
NASA NTRS1991

ISE advanced technology

Information on Space Station Freedom scheduling problems and techniques are presented in viewgraph form. Topics covered include automated scheduling systems, user interface standards, benefits of interactive scheduling systems, incremental scheduling, software engineering, computer graphics interface, distributed resource management, and advanced applications.

Fox, Barry R.↗
NASA NTRS1992

Plasma wave profiles of earth's bow shock at low Mach numbers - ISEE 3 observations on the far flank

A survey of selected crossings far downstream from the subsolar shock is presented in which the overall plasma wave (PW) behavior of a selected set of nearly perpendicular crossings and another set of limited Mach number but broad geometry are delinated. The result is a generalizable PW signature, or signatures, of low Mach number shocks and some likely implications of those signatures for the weak shock's plasma physical processes on the flank. The data are found to be consistent with the presence of ion beam interactions producing noise ahead of the shock in the ion acoustic frequency range. The presence or absence, and the amplitudes, of PW activity are explainable by the presence or absence of a population of upstream ions controlled by the component of the interplanetary magnetic field normal to the solar wind flow.

Greenstadt, E. W.↗
NASA NTRS1993

Bidirectional about 1 MeV/amu ion intervals in 1973-1991 observed by the Goddard Space Flight Center instruments on IMP 8 and ISEE 3/ICE

Bidirectional energetic ion flows (BIFs) in the solar wind at 1AU during 1973-1991 are examined on the basis of about 1 MeV/amu data from the Goddard Space Flight Center instruments on ISEE3/ICE and IMP 8. BIFs are observed more frequently around solar maximum, when they are observed about 12 percent of the time compared with about 5 percent at solar minimum. Intervals with durations greater than 4 hr are observed on average approximately every 3-4 d at solar maximum and every 2 wk at solar minimum, with about 33 percent of these intervals following within 2 d of an interplanetary shock. Various coronal mass ejection signatures and BIFs greater than 1 MeV/amu usually do not coincide exactly, and additional bidirectional ion events are identified.

Richardson, I. G.↗
NASA NTRS1993

The quasiperpendicular environment of large magnetic pulses in Earth's quasiparallel foreshock - ISEE 1 and 2 observations

ULF waves in Earth's foreshock cause the instantaneous angle theta-B(n) between the upstream magnetic field and the shock normal to deviate from its average value. Close to the quasi-parallel (Q-parallel) shock, the transverse components of the waves become so large that the orientation of the field to the normal becomes quasi-perpendicular (Q-perpendicular) during applicable phases of each wave cycle. Large upstream pulses of B were observed completely enclosed in excursions of Theta-B(n) into the Q-perpendicular range. A recent numerical simulation included Theta-B(n) among the parameters examined in Q-parallel runs, and described a similar coincidence as intrinsic to a stage in development of the reformation process of such shocks. Thus, the natural environment of the Q-perpendicular section of Earth's bow shock seems to include an identifiable class of enlarged magnetic pulses for which local Q-perpendicular geometry is a necessary association.

Greenstadt, E. W.↗
NASA NTRS1994

A detailed examination of a X-line region in the distant tail: ISEE-3 observations of jet flow and B(sub z) reversals and a pair of slow shocks

We report an observation of Petschek-type magnetic reconnection at a distant neutral line (X = -230 R(sub e)) with a full set of signatures of the magnetic merging process. These features include a reversal of plasma flows from earthward to tailward, a pair of slow shocks and the magnetic field X-type line. These two slow shocks are shown to satisfy the shock criteria used by Feldman et al. (1987). The spacecraft first crosses a slow shock to enter the earthward flowing plasmasheet with velocity of about 440 km/s. The embedded magnetic field has a positive B(sub z) component. The spacecraft next enters a region of tailward plasma flow with speed approximately 670 km/s and an embedded negative B(sub z), indicating entry into the plasmasheet tailward of the X-line. These observed velocities are comparable to calculated velocities based on Rankine-Hugoniot conservation relationships. The spacecraft subsequently returns into the south tail lobe by crossing another slow shock. Coplanarity analyses shows that the two slow shocks have orientations consistent with that predicted by the Petschek reconnection model. We note that this event occurs during northward interplanetary magnetic fields. Thus, a magnetic stress built-up in the distant tail may be responsible for this reconnection process.

Ho, C. M.↗