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At least 1,225 records · Page 68
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Properties of an impulsive compact solar flare determined from Solar Maximum Mission X-ray measurements

Soft X-ray, hard X-ray magnetogram, and H-alpha data have been analyzed for an impulsive compact solar flare which occurred on May 21, 1985. The derived flare loop dimensions are about 20,000 km length and about 150 km diameter. Measurements of line ratios from the Mg XI ion indicate that the plasma density varied from about 4 x 10 to the 12th/cu cm early in the flare to about 10 to the 12th/cu cm during the flare decay. The initial temperature of this plasma was about 8 x 10 to the 6th K and dropped to about 5 x 10 to the 6th K during the decay phase. The simplest interpretation of the event is one in which the source of the soft X-ray flare emission is confined to a thin loop of very high density.

Linford, G. A.↗
NASA NTRS1988

Collaborative analysis of solar maximum mission, Venera and Prognoz solar X-ray bursts

Efforts centered on cross-calibrating the Solar Maximum Mission (SMM) HXRBS detector with the Venera 13/14 cosmic ray burst detectors. The event was divided into six time intervals, and the best fitting SMM and Venera 13 spectra were calculated for each interval, using the individual fitting routines for the two instruments. The results are presented and discussed.

Hurley, Kevin C.↗
NASA NTRS1988

Solar neutron observations and their relation to solar flare acceleration problems

The current observational knowledge on the production of neutrons in association with solar flares is reviewed. From a study of the observations, it is shown that unique information can be obtained on the spectral properties of accelerated ions produced during the flare. Also, the abundance of He-3/H in the photosphere can be directly determined. The current interpretations of all available neutron observations and in particular highlight the uncertainties are also reviewed.

Chupp, E. L.↗
NASA NTRS1989

Conceptual design study of a 5 kilowatt solar dynamic Brayton power system using a dome Fresnel lens solar concentrator

The primary project objective was to generate a conceptual design for a nominal 5 kW solar dynamic space power system, which uses a unique, patented, transmittance-optimized, dome-shaped, point-focus Fresnel lens as the optical concentrator. Compared to reflective concentrators, the dome lens allows 200 times larger slope errors for the same image displacement. Additionally, the dome lens allows the energy receiver, the power conversion unit (PCU), and the heat rejection radiator to be independently optimized in configuration and orientation, since none of these elements causes any aperture blockage. Based on optical and thermal trade studies, a 6.6 m diameter lens with a focal length of 7.2 m was selected. This lens should provide 87 percent net optical efficienty at 800X geometric concentration ratio. The large lens is comprised of 24 gores, which compactly stow together during launch, and automatically deploy on orbit. The total mass of the microglass lens panels, the graphite/epoxy support structure, and miscellaneous hardware is about 1.2 kg per square meter of aperture. The key problem for the dome lens approach relates to the selection of a space-durable lens material. For the first time, all-glass Fresnel lens samples were successfully made by a sol-gel casting process.

Oneill, Mark J.↗
NASA NTRS1988

Data catalog series for space science and applications flight missions. Volume 5A: Descriptions of astronomy, astrophysics, and solar physics spacecraft and investigations. Volume 5B: Descriptions of data sets from astronomy, astrophysics, and solar physics spacecraft and investigations

The main purpose of the data catalog series is to provide descriptive references to data generated by space science flight missions. The data sets described include all of the actual holdings of the Space Science Data Center (NSSDC), all data sets for which direct contact information is available, and some data collections held and serviced by foreign investigators, NASA and other U.S. government agencies. This volume contains narrative descriptions of data sets of astronomy, astrophysics, solar physics spacecraft and investigations. The following spacecraft series are included: Mariner, Pioneer, Pioneer Venus, Venera, Viking, Voyager, and Helios. Separate indexes to the planetary and interplanetary missions are also provided.

Kim, Sang J.↗
NASA NTRS1992

Comparison of high-resolution solar irradiance spectra and the solar luminosity in the period 1980-1989

In this research, we aim to determine to what extent the solar irradiance changes measured through the 1980's from orbiting vehicles are accompanied by spectroscopic irradiance changes observable from the ground. We describe fractional changes in line absorption as 'blanketing'. In section 2, we briefly review results obtained in an earlier project and which have been published. Section 3 describes the data of this investigation; section 4 describes the data reduction; section 5 describes the observational results in terms of blanketing; and section 6 describes the interpretation of the measured changes. Section 7 contains an outline of possible uses for Doppler-shift data that emerges with the measurements of the blanketing variations. Section 8 is an outline for future research suggested by our results in this project.

Mitchell, Walter E., Jr.↗
NASA NTRS1992

The cause of the coronal temperature inversion of the solar atmosphere and the implications for the solar wind

The energy contained in suprathermal tails at the base of the transition region is shown to be transformed into the rarefied, but hotter, transition region and low corona without any further addition of energy to the gas above the base of the transition region. Possible critical point location and asymptotic wind speed are shown to be controlled by the suprathermal tail strength parameter used to model possible suprathermal velocity distribution functions at the base of the transition region. This process shows promise for producing temperature profiles that peak near, but outside of, the fluid critical point without ad hoc energy deposition. The coronal temperature inversion above the solar photosphere is argued to be a generic feature around all stars with nonthermal distributions at the heights where the atmosphere last becomes mostly ionized.

Scudder, J. D.↗
NASA NTRS1992

Solar-wind/magnetospheric dynamos: MHD-scale collective entry of the solar wind energy, momentum and mass into the magnetosphere

A quasi open MHD (Magnetohydrodynamic) scale anomalous transport controlled boundary layer model is proposed, where the MHD collective behavior of magnetofluids (direct dynamo effect, anomalous viscous interaction and anomalous diffusion of the mass and the magnetic field) plays the main role in the conversion of the Solar Wind (SW) kinetic and magnetic energy into electromagnetic energy in the Magnetosphere (MSp). The so called direct and indirect dynamo effects are based on inductive and purely dissipative energy conversion, respectively. The self organization ability of vector fields in turbulent magnetofluids implies an inductive response of the plasma, which leads to the direct dynamo effect. The direct dynamo effect describes the direct formation of localized field aligned currents and the transverse Alfven waves and provides a source for MHD scale anomalous diffusivity and viscosity. The SW/MSp coupling depends on the dynamo efficiency.

Song, Yan↗
NASA NTRS1993

Biological effects and physics of solar and galactic cosmic radiation, Part B; Proceedings of a NATO Advanced Study Institute on Biological Effects and Physics of Solar and Galactic Cosmic Radiation, Algarve, Portugal, Oct. 13-23, 1991

Since there is an increasing interest in establishing lunar bases and exploring Mars by manned missions, it is important to develop appropriate risk estimates and radiation protection guidelines. The biological effects and physics of solar and galactic cosmic radiation are examined with respect to the following: the radiation environment of interplanetary space, the biological responses to radiation in space, and the risk estimates for deep space missions. There is a need for a long-term program where ground-based studies can be augmented by flight experiments and an international standardization with respect to data collection, protocol comparison, and formulation of guidelines for future missions.

Swenberg, Charles E.↗
NASA NTRS1996

Solar cycle dynamics of solar, magnetospheric, and heliospheric particles, and long-term atmospheric coupling: SAMPLEX

This report summarizes science analysis activities by the SAMPEX mission science team during the period during the period July 1, 1995 through July 1, 1996. Bibliographic entries for 1995 and 1996 to date (July 1996) are included. The SAMPEX science team was extremely active, with 20 articles published or submitted to refereed journals, 18 papers published in their entirety in Conference Proceedings, and 53 contributed papers, seminars, and miscellaneous presentations. The bibliography at the end of this report constitutes the primary description of the research activity. Science highlights are given under the major activity headings of anomalous cosmic rays, solar energetic particles, magnetospheric precipitating electrons, trapped H and He isotopes, and data analysis activities.

Mason, G. M.↗
NASA NTRS1996

Energetics of impulsive solar flares: Correlating BATSE hard x-ray bursts and the solar atmosphere's soft x-ray response

This investigation has involved the correlation of BATSE-observed solar hard X-ray emission with the characteristics of soft X-ray emitting plasma observed by the Yohkoh Bragg Crystal Spectrometers. The goal was to test the hypothesis that localized electron beam heating is the dominant energy transport mechanism in impulsive flares, as formulated in the thick-target electron-heated model of Brown.

Newton, Elizabeth↗
NASA NTRS1999

The Influence of Extremely Large Solar Proton Events in a Changing Stratosphere. Stratospheric Influence of Solar Proton Events

Two periods of extremely large solar proton events (SPEs) occurred in the past thirty years, which forced significant long-term polar stratospheric changes. The August 2-10, 1972 and October 19-27, 1989 SPEs happened in stratospheres that were quite different chemically. The stratospheric chlorine levels were relatively small in 1972 (approximately 1.2 ppbv) and were fairly substantial in 1989 at about (approximately 3 ppbv). Although these SPEs produced both HO(x) and NO(y) constituents in the mesosphere and stratosphere, only the NO(y) constituents had lifetimes long enough to affect ozone for several months to years past the events. Our recently improved two-dimensional chemistry and transport atmospheric model was used to compute the effects of these gigantic SPEs in a changing stratosphere. Significant upper stratospheric ozone depletions > 10% are computed to last for a few months past these SPEs. The long-lived SPE-produced NO(y) constituents were transported to lower levels during winter after these huge SPEs and caused impacts in the middle and lower stratosphere. During periods of high halogen loading these impacts resulted in interference with the chlorine and bromine loss cycles for ozone destruction. The chemical state of the atmosphere, including the stratospheric sulfate aerosol density, substantially affected the predicted stratospheric influence of these extremely large SPEs.

Jackman, Charles H.↗
NASA NTRS2001

Formation and Early Evolution of Solar and Extra-Solar Giant Planets

This project investigates the origin of giant planets, both in the Solar System and around other stars. It is assumed that the planets form by the core accretion process: small solid particles in a disk surrounding a young star gradually coagulate into objects of a few kilometers in size, known as planetesimals, which then accumulate into solid protoplanetary cores. Once the cores have become large enough, they are able to attract gas from the surrounding disk to form the deep gaseous envelope of the giant planet. Our code simulates giant planet growth in a spherical approximation, and it has been quite successful in addressing a number of basic planetary properties. Further improvements to the code have been made to achieve a more realistic understanding of planetary formation. The computations of the models were based on an earlier version of our code and were stopped at the onset of runaway gas accretion. Now, improved boundary conditions have been incorporated into the code to allow for hydrodynamic inflow of gas and to handle the late stages of evolution when the planet evolves at constant mass. These changes were made to the version of the code that uses a constant accretion rate and to the version that uses a self-consistent method for calculating both the solid and gas accretion rates. The equation of state has been updated to incorporate the detailed tables of Saumon, Chabrier, and Van Horn. The opacities were updated to include the results of Alexander and Ferguson. The outer boundary conditions were modified. During the accretion phase when the planet's radius is between the accretion radius and the tidal radius, we set the outer boundary at a 'modified' accretion radius, which is the point where thermal energy is enough to bring gas to the edge of the Hill sphere.

Bodenheimer, P. H.↗
NASA NTRS2004

The Development of Solar Sail Propulsion for NASA Science Missions to the Inner Solar System

This paper examines recent assessments of the technology challenges facing solar sails, identifies the systems and technologies needing development, and the approach employed by NASA's In-space Propulsion Program in NASA to achieve near term products that move this important technology from low technology readiness level (TRL) toward the goal of application to science missions in near earth space and beyond. The status of on-going efforts to design, build, and test ground demonstrators of alternate approaches to structures (inflatable versus rigid), membrane materials, optical shape sensing, and attitude control will be presented along with planned future investments.

Montgomery, Edward E, IV↗
NASA NTRS2004

Development of Solar Sail Propulsion for Inner Solar System NASA Science Missions

This paper examines recent assessments of the technology challenges facing solar sails, identifies the systems and technologies needing development, and the approach employed by NASA's In-Space Propulsion program in NASA to achieve near-term products that move this important technology from low technology readiness level toward the goal of application to science missions in near-Earth space and beyond.

Montgomery, Edward E., IV↗