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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 181 records · Page 10
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NASA NTRS1980

Spacecraft measurements of the elemental and isotopic composition of solar energetic particles

Within the past few years, instruments flown on satellites and space probes have made significant progress in measuring the elemental and isotopic composition of energetic heavy nuclei accelerated in solar flares. These new observations are discussed, focusing on: (1) the energy dependence of the elemental composition at energies not greater than 1 MeV/nucleon; (2) flare to flare variations in the composition; and (3) comparisons of the average solar particle abundances (Z not less than 2 and not greater than 28) with other measures of the solar composition, including photospheric, coronal, and solar wind observations. These comparisons have led to the suggestion that solar flares sample the composition of the corona. Isotopic measurements of heavy solar flare nuclei have recently added a new dimension to these studies. In particular, the isotopic composition of solar flare neon has been found to be significantly different from that measured in the solar wind, but consistent with the meteoritic component neon-A.

Mewaldt, R. A.↗
NASA NTRS2018

The Probability of False Go/No-Go Determined by GOES Proton Flux: Proposed Launch Constraints for Avoiding Damaging Solar Energetic Particle Events

Most space-bound hardware needs to be designed to withstand space weather events to some degree. Long-term predictability of space weather events, such as solar flares or coronal mass ejections, are still a matter of theory so designers should assume a worst case event for their specific environment. In our analysis, we show preliminary results of the probability of encountering a false/true go/no-go based on a threshold launch and design proton environment. The goal in choosing a threshold launch environment is to avoid the chance of exceeding the design environment during vulnerable parts of the mission. Operationally, this method cannot predict damaging space weather but can aid in avoiding space weather events that are already occurring. The GOES (Geostationary Operational Environmental Satellite) proton flux database is used as a proxy for the heavy ion fluxes, which impart a greater threat because of larger single event upsets and effects. Our use of protons as a proxy for heavy ions is justified on the basis of the correlation between their fluxes shown by a qualitative comparison of GOES proton integral fluxes at greater than 10 megaelectronvolts and ACE/SIS (Advanced Composition Explorer / Solar Isotope Spectrometer) heavy ion integral fluxes.

DeStefano, Anthony M.↗
NASA NTRS1980

Elemental composition of solar energetic particles in 1977 and 1978

Measurements of the elemental composition of energetic nuclei with atomic numbers between 2 and 28 from seven major solar flares from September 1977 to May 1978 are presented. The abundance observations were made with the Low Energy Telescope systems of the cosmic ray detector systems on board the Voyager 1 and 2 spacecraft between 1 and 3 AU. Examination of the abundance ratios of the flare nuclei relative to oxygen reveals significant variations from event to event and between energetic nuclei and photospheric abundances, with an average composition, except for C and N, very similar to that of the galactic cosmic ray source. For the four flare events for which the elemental abundances exhibit no significant energy dependence in the energy range observed, it is found that the enhancement of energetic nuclei relative to their photospheric abundance are similar and not monotonic with atomic number, with the metallic nuclei showing an enhancement factor of approximately 5 and the volatiles showing one closer to 1.

Cook, W. R.↗
NASA NTRS2001

Correlation of Upper-Atmospheric Be-7 With Solar Energetic Particle Events

Surprisingly large concentrations of radioactive Be-7 have been found in the upper atmosphere at levels of one to three orders of magnitude greater than observed in the stratosphere. This phenomenon was originally observed on the LDEF satellite which was recovered in January 1990 following a period of extremely high solar activity in the fall of 1989. We report on follow-up measurements on the Russian COSMOS and RESURS F1 spacecraft during the period of 1996 to 1999 which was a period of minimal to moderate solar activity. The Be-7 concentrations observed on these flights were down substantially from the LDEF observations but were still one to two orders of magnitude higher than stratospheric levels. A significant correlation is observed between the Be-7 activity and the combined fluence of solar energetic protons (SEP) and galactic cosmic-ray (GCR) protons. The Be-7 activity is not correlated with overall solar activity as represented by the solar x-ray flux. We discuss possible mechanisms for the solar proton correlation. However, it is likely that the Be-7 is ionized and it is unknown how this will affect the calculations. There were several large solar flares in the fall of 1989 that produced extraordinarily intense solar particle events at the Earth and record geophysical disturbances. These may have acted to increase production of Be-7 from spallation in the stratosphere and also to enhance transport to higher altitudes from the effects of heating and expansion of the upper atmosphere. Be-7 in the upper atmosphere may also have been produced directly at the Sun. Be-7 and Li-7 are produced in solar flares when accelerated alpha-particles fuse with He-4 in the solar atmosphere. Under optimistic assumptions for Sun to Earth transport and subsequent insertion into low Earth orbit, a Be-7 density of about 10(exp -7) atom/cubic cm at 310 km is estimated.

Phillips, G. W.↗
NASA NTRS1988

The role of interplanetary shocks in the longitude distribution of solar energetic particles

Data from the Goddard particle experiments on IMPs 4, 5, 7, and 8, and ISEE 3 are used to model particle intensity profiles including prompt solar particles and the effects of shocks. It is shown that the intensity profiles of solar protons depend on the heliolongitude, and it is suggested that the major controlling agent is the existence of an interplanetary (IP) shock. Shocks are strongest when observed along the radial from the source region, with the highest shock-associated intensities generally observed from central meridian flares. Using a recently derived model for the large-scale structure of IP shocks, the change in shape as a function of heliolongitude is explained.

Cane, H. V.↗
NASA NTRS1991

Radial propagation of solar energetic particles assuming large scattering mean free paths in the interplanetary medium

Observations of two flares which fit the diffusive model by Beeck et al. (1987) are employed to determine whether large solar-particle events can be explained by the mechanisms of small impulsive events. It is shown that the injection of particles at the source is extended in time and lasts more than approximately 10 hours. The extended injection at the sun is hypothesized to be the reason that large solar particles do not demonstrate the 'pulse/wake' behavior associated with the small impulsive events.

Mason, G. M.↗
NASA NTRS1983

Elemental and isotopic composition of solar energetic particles - Preliminary results from the Phoenix I telescope

The Phoenix I instrument on the S81-1 mission was designed to resolve isotopes in the charge range He to Ni. Analysis of four periods of moderate flare activity shows no strong evidence for mass dependent acceleration in the range C to Si; indeed, the mass abundance ratios are consistent with 'solar system' composition. However, the average Ne-22/Ne-20 ratio for these periods is 0.060 (+0.045, -0.023), i.e. about one standard deviation below ratios reported earlier for solar energetic neon.

Simpson, J. A.↗
NASA NTRS1974

Variability of intensity ratios of H to He and He to ions with Z not smaller than 3 in solar energetic particle events

Data from the solid-state detector on Explorer 35 are applied to a study of two intensity ratios in the sub-MeV per nucleon specific kinetic energy range for several energetic particle events. It is found that the intensity ratios vary markedly from event to event, particularly during the time history of the individual events. This implies that the ratios have no simple relationship to 'solar abundances' in the usual sense of the term. The pattern of the variability of each ratio is established; the ratio of He to ions with Z not smaller than 3 starts with a low value and increases as the event proceeds. The H/He ratio exhibits a qualitatively similar time history with marked relative enhancement of He early in an event. Differential diffusion of the various ionic species with differing magnetic rigidities is seen to be the dominant physical cause for the variabilities observed.

Van Allen, J. A.↗
NASA NTRS1991

Abundance variations in solar energetic particles

Abundance variations are examined in a large number of events including smaller nonimpulsive events not previously considered. Whereas a comparison at equal energy per nucleon is appropriate for heavy ions this is not the case when including H. The best representation is either in terms of rigidity or energy per charge depending on the type of event under consideration. For the majority of large events, where particles are primarily accelerated at interplanetary shocks, if abundances relative to H are evaluated at equal energy per charge then abundance ratios are compatible with solar wind values and spectral shapes agree. Furthermore the behavior of H is then compatible with that of other high FIP elements.

Cane, H. V.↗
NASA NTRS1985

Pitch Angle Distributions of Solar Energetic Particles and the Local Scattering Properties of the Interplanetary Magnetic Field

An approximate solution of the Fokker-Planck equation containing pitch angle scattering and adiabatic focusing is discussed. For modest focusing effects the omnidirectional density obeys an ordinary diffusion equation with a modified diffusion coefficient. The anisotropic part of the distribution function is properly normalized and split into an even and an odd part. The even part is determined by the ratio between the scattering mean free path and the focusing length and by the degree of polarization of the magnetic field fluctuations. The odd part is determined by the deviation of the pitch angle scattering from isotropic scattering. The method supplies a powerful tool to obtain the local characteristics of pitch angle scattering. It is insensitive to long lasting solar injections and to moderate radial variations of the mean free path. The method is applied to solar particle events observed on Helio-1 and -2.

Beeck, J.↗
NASA NTRS2011

Probabilistic Solar Energetic Particle Models

To plan and design safe and reliable space missions, it is necessary to take into account the effects of the space radiation environment. This is done by setting the goal of achieving safety and reliability with some desired level of confidence. To achieve this goal, a worst-case space radiation environment at the required confidence level must be obtained. Planning and designing then proceeds, taking into account the effects of this worst-case environment. The result will be a mission that is reliable against the effects of the space radiation environment at the desired confidence level. In this paper we will describe progress toward developing a model that provides worst-case space radiation environments at user-specified confidence levels. We will present a model for worst-case event-integrated solar proton environments that provide the worst-case differential proton spectrum. This model is based on data from IMP-8 and GOES spacecraft that provide a data base extending from 1974 to the present. We will discuss extending this work to create worst-case models for peak flux and mission-integrated fluence for protons. We will also describe plans for similar models for helium and heavier ions.

Adams, James H., Jr.↗