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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 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
NASA NTRS1996

Doppler Measurements of the Suns Meridional Flow

Doppler velocity data obtained with the Global Oscillation Network Group (GONG) instruments in Tucson from 1992 August through 1995 April were analyzed to determine the structure and evolution of the Sun's meridional flow. Individual measurements of the flow were derived from line-of-sight velocity images averaged over 17 minutes to remove the p-mode oscillation signal. Typical flow velocities are poleward at approximately 20 m/s, but the results suggest that episodes may occur with much stronger flows. Such variations may help to explain some of the many disparate reports on the strength and structure of the Sun's meridional flow.

Hathaway, David H.↗
NASA NTRS1997

The Ambient and Perturbed Solar Wind: From the Sun to 1 AU

The overall objective of the proposed research was to use numerical solutions of the magnetohydrodynamic (MHD) equations along with comparisons of the computed results with observations to study the following topics: (1) ambient solar wind solutions that extend from the solar surface to 1 astronomical unit (AU), contain closed magnetic structures near the Sun, and are consistent with observed values; (2) magnetic and plasma structures in coronal mass ejections (CMES) as they propagate to the interplanetary medium; (3) relation of MHD shocks to CMEs in the interplanetary medium; (4) interaction of MHD shocks with structures (such as other shocks, corotating interaction regions, current sheets) in the interplanetary plasma; and (5) simulations of observed interplanetary structures. A planned close collaboration with data analysts served to make the model more relevant to the data. The outcome of this research program is an improved understanding of the physical processes occurring in solar-generated disturbances in the interplanetary medium between the Sun and 1 AU.

Steinolfson, R. S.↗
NASA NTRS1997

Understanding the He II 304A resonance line in the sun

The data acquired by the coronal diagnostic spectrometer (CDS) and the solar ultraviolet measurement of emitted radiation (SUMER) instrument onboard the Solar and Heliospheric Observatory (SOHO) are discussed. The hypothesis that the 304 A line is formed by collisional excitation in the quiet sun is analyzed. The SOHO data allowed a better evaluation of both the transition-region condition and of photoionizing coronal flux to be performed. Recent quiet sun series of coordinated observations taken during May 1997 are summarized.

Jordan, S.↗
NASA NTRS1997

A spacecraft going behind the Sun will support SOHO

The problems that can be solved by combining the Solar and Heliospheric Observatory (SOHO) and the magnetic structures on and around the sun (MagSonas) observations are discussed. A magneto-Doppler imager and X and Ka band linearly polarized radio signals sent to the other side of the sun can support extended SOHO mission. This is the purpose of the MagSonas mission. The MagSonas radio system, designed to serve as spacecraft communications and a sounding coronal magnetic field, is described.

Ruzmaikin, A.↗
NASA NTRS1998

The Sun in Time

Using a grant from NASA's Initiative to Develop Education through Astronomy and Space Science (IDEAS) program, we have developed an inter-disciplinary curriculum for middle-school students which targets both history and astronomy. Our curriculum explores the attitudes and techniques of ancient spiritual leaders, specifically those of the Maya and Inca cultures, who observed and tried to control the Sun. We wish students to understand the probable importance of astronomical observations to these ancient peoples. In addition, using the experience of an archaeologist, we show how modern techniques of viewing the Earth through satellite imagery, has allowed the re-discovery of ancient sites where solar observations and attempted manipulation of the universe took place. To contrast ancient observations of the Sun with modern ones, we use the experience of a solar astronomer and bring to the classroom up-to-date information about solar astronomy and the impact of solar activity on the Earth's environment. In this presentation, we will present fragments of our curriculum as well as results from pre- and post-tests given to participating groups of students. Finally, we will discuss comments from local middle-school teachers who were asked to evaluate our curriculum.

Adams, Mitzi L.↗
NASA NTRS2000

Turbulent Eddy Viscosity and Large-Scale Convection in the Sun

It is suggested here that the laminar character of the large-scale deep convective flows appearing in numerical simulations of the Sun's convective envelope arises from the effect of turbulent eddy viscosity. Previously, M. Schwarzchild suggested the same idea to explain the observed surface granulation in the Sun.

Stothers, Richard B.↗
NASA NTRS2001

Two-Component Fitting of Coronal-Hole and Quiet-Sun He I 1083 Spectra

We present reduction techniques and first results for detailed fitting of solar spectra obtained with the NASA/National Solar Observatory Spectromagnetograph (NASA/NSO SPM over a 2 nm bandpass centered on the He 1 1083 nm line. The observation for this analysis was a spectra-spectroheliogram obtained at the NSO/Kitt Peak Vacuum Telescope (KPVT) on 00 Apr 17 at 21:46 UT spanning an area of 512 x 900 arc-seconds; the field of view included a coronal hole near disk center as well as surrounding quiet sun. Since the He I line is very weak and blended with nearby solar and telluric lines, accurate determination of the continuum intensity as a function of wavelength is crucial. We have modified the technique of Malanushenko {\it et al.) (1992; {\it AA) (\bf 259), 567) to tie regions of continuua and the wings of spectral lines which show little variation over the image to standard reference spectra such as the NSO Fourier Transform Spectrometer atlas (Wallace {\it et al). 1993; NSO Tech Report \#93-001). We performed detailed least-squares fits of spectra from selected areas, accounting for all the known telluric and solar absorbers in the spectral bandpass. The best physically consistent fits to the Helium lines were obtained with Gaussian profiles from two components (one ''cool'', characteristic of the upper chromosphere; one ''hot'', representing the cool transition region at 2-3 x 10$^{4)$ K). In the coronal hole, the transition-region component, shifted by 6-7 km/s to the blue, is mildly dominant, consistent with mass outflow as suggested by Dupree {\it et all. (1996; {\it Ap. J.}-{\bf 467), 121). In quiet-sun spectra there is less evidence of outward flow, and the chromospheric component is more important. All our fitted spectra show a very weak unidentified absorption feature at 1082.880 nm in the red wing of the nearby Si I line.

Jones, Harrison P.↗
NASA NTRS2001

Teaching About the Sun-Earth Connection

This talk will be about the Sun: how it changes with time, its magnetic cycle, flares, and the solar wind. The solar wind and what space is like between the Sun and Earth will be presented. Also, the Earth, its magnetic field, how the solar wind interacts with the Earth, Aurora, and how these affect human systems will be discussed. These interactions dictate how we build our systems in space (communications satellites, GPS, etc), and some of our ground systems (power grids). Some simple classroom activities will be presented that can be done using new data from space that is available daily on the internet, and how you can use the internet to get space questions answered within about 1 day. Finally, some career opportunities for jobs related to space for the future will be discussed.

Poland, Arthur I.↗
NASA NTRS2002

Fine Sun Sensor Field of View Calibration

The fine Sun sensor (FSS) used on many spacecraft consists of two independent single-axis sensors, nominally mounted perpendicularly, that detect Sun angle across a typical field of view of +/- 32 degrees. The nonlinear function that maps the measured counts into an observed angle is called the transfer function. The FSS transfer function provided by the manufacturer consists of nine parameters for each of the two sensitive axes. An improved transfer function has been previously reported that achieves a significant accuracy improvement across the entire field of view. This new function expands the parameter set to 12 coefficients per axis and includes cross terms combining counts from both axes. To make best use of the FSS for spacecraft attitude determination, it must be calibrated after launch. We are interested in simplifying the postlaunch calibration procedure for estimating improvements to the 24 parameters in the transfer function. This paper discusses how to recombine the terms of the transfer function to reduce their redundancy without decreasing its accuracy and then presents an attitude dependent procedure for estimating the parameters. The end result is a calibration algorithm that is easier to use and does not sacrifice accuracy. Results of calibration using on-orbit data are presented.

Sedlak, Joseph E.↗
NASA NTRS2002

The Sun: Our Nearest Star

We have in our celestial backyard, a prime example of a variable star. The Sun, long thought to be "perfect" and unvarying, began to reveal its cycles in the early 1600s as Galileo Galilei and Christoph Scheiner used a telescope to study sunspots. For the past four hundred years, scientists have accumulated data, showing a magnetic cycle that repeats, on average, every eleven (or twenty-two) years. In addition, modern satellites have shown that the energy output at radio and x-ray wavelengths also varies with this cycle. This talk will showcase the Sun as a star and discuss how solar studies may be used to understand other stars.

Adams, M. L.↗
NASA NTRS2002

Solar Wind Characteristics from SOHO-Sun-Ulysses Quadrature Observations

Over the past few years, we have been running SOHO (Solar and Heliospheric Observatory)-Sun-Ulysses quadrature campaigns, aimed at comparing the plasma properties at coronal altitudes with plasma properties at interplanetary distances. Coronal plasma has been observed by SOHO experiments: mainly, we used LASCO (Large Angle and Spectrometric Coronagraph Experiment) data to understand the overall coronal configuration at the time of quadratures and analyzed SUMER (Solar Ultraviolet Measurements of Emitted Radiation), CDS (Coronal Diagnostic Spectrometer) and UVCS (Ultraviolet Coronagraph Spectrometer) data to derive its physical characteristics. At interplanetary distances, SWICS (Solar Wind Ion Composition Spectrometer) and SWOOPS (Solar Wind Observation over the Poles of the Sun) aboard Ulysses provided us with interplanetary plasma data. Here we report on results from some of the campaigns. We notice that, depending on the geometry of the quadrature, i.e. on whether the radial to Ulysses traverses the corona at high or low latitudes, we are able to study different kinds of solar wind. In particular, a comparison between low-latitude and high-latitude wind, allowed us to provide evidence for differences in the acceleration of polar, fast plasma and equatorial, slow plasma: the latter occurring at higher levels and through a more extended region than fast wind. These properties are shared by both the proton and heavy ions outflows. Quadrature observations may provide useful information also on coronal vs. in situ elemental composition. To this end, we analyzed spectra taken in the corona, at altitudes ranging between approx. 1.02 and 2.2 solar radii, and derived the abundances of a number of ions, including oxygen and iron. Values of the O/Fe ratio, at coronal levels, have been compared with measurements of this ratio made by SWICS at interplanetary distances. Our results are compared with previous findings and predictions from modeling efforts.

Poletto, Giannina↗
NASA NTRS2002

The Sun's Impact on Climate

We provide an overview of the impact of the Sun on the Earth atmosphere and climate system, focused on heating of Earth's atmosphere and oceans. We emphasize the importance of the spectral measurements of SIM and SOLSTICE- that we must know how solar variations are distributed over ultraviolet, visible, and infrared wavelengths, since these have separate characteristic influences on Earth's ozone layer, clouds, and upper layers of the oceans. Emphasis is also given to understanding both direct and indirect influences of the Sun on the Earth, which involve feedbacks between Earth's stratosphere, troposphere, and oceans, each with unique time scales, dynamics, chemistry, and biology, interacting non-linearly. Especially crucial is the role of all three phases of water on Earth, water vapor being the primary greenhouse gas in the atmosphere, the importance of trace gases such as CO2 arising from their absorption in the "water vapor window" at 800 - 1250/cm (12.5 to 8 microns). Melting of polar ice is one major response to the post-industrial global warming, enhanced due to "ice-albedo" feedback. Finally, water in liquid form has a major influence due to cloud albedo feedback, and also due to the oceans' absorption of solar radiation, particularly at visible wavelengths, through the visible "liquid water window" that allows penetration of visible light deep into the mixed layer, while nearby ultraviolet and infrared wavelengths do not penetrate past the upper centimeter ocean surface skin layer. A large fraction of solar energy absorbed by the oceans goes into the latent heat of evaporation. Thus the solar heating of the atmosphere-ocean system is strongly coupled through the water cycle of evaporation, cloud formation, precipitation, surface runoff and ice formation, to Earth's energy budget and climate, each different climate component responding to variations in different solar spectral bands, at ultraviolet, visible and infrared wavelengths.

Cahalan, Robert↗
NASA NTRS2002

Servicing and Deployment of National Resources in Sun-Earth Libration Point Orbits

Spacecraft travel between the Sun-Earth system, the Earth-Moon system, and beyond has received extensive attention recently. The existence of a connection between unstable regions enables mission designers to envision scenarios of multiple spacecraft traveling cheaply from system to system, rendezvousing, servicing, and refueling along the way. This paper presents examples of transfers between the Sun-Earth and Earth-Moon systems using a true ephemeris and perturbation model. It shows the (Delta)V costs associated with these transfers, including the costs to reach the staging region from the Earth. It explores both impulsive and low thrust transfer trajectories. Additionally, analysis that looks specifically at the use of nuclear power in libration point orbits and the issues associated with them such as inadvertent Earth return is addressed. Statistical analysis of Earth returns and the design of biased orbits to prevent any possible return are discussed. Lastly, the idea of rendezvous between spacecraft in libration point orbits using impulsive maneuvers is addressed.

Folta, David C.↗
NASA NTRS2003

Living with a Star: New Opportunities in Sun-Climate Research

Enormous advances have been made in the last quarter century in all of these needed areas, covering the two essential halves of the Sun-Climate question: in what we know of solar variations and, equally important, in what we know of the climate system and of climatic changes. These research achievements allow us to examine all aspects of the question more directly and quantitatively than was ever possible before, and in the brighter light and more objective context of other known or suspected climate change mechanisms, including human-induced global greenhouse warming. Brief summaries of present status and current understanding are given below for nine facets of Sun-Climate science in which major progress has been made in recent years. At the same time it will be seen that in every instance, significant elements of uncertainty still remain, Some of the most important of these unanswered questions are considered later, in Section IV.

Eddy, John Allen↗
NASA NTRS2004

Zonal Flows Below the Sun's Convection: Analytic Approximation

We have derived a simple analytic solution showing how the Sun's global oscillations (g-modes) can drive east-west flows at low latitude deep inside the Sun. This flow is analogous to the Quasi Biennial Oscillation in the Earth s upper atmosphere. It has an observed period of 1.3 years in the solar case but its cause was not known until we published an explanation in a Letter to the Editor a few months ago. Now we give full details of the model and show how it can be used to limit the range of g-modes that can be actively driving the reversing flows. A nonlinear feedback feature of the model is that the flow itself creates the turbulent dissipation that extracts momentum from the g-modes that, in turn, drives the flow.

Wolff, Charles L.↗
NASA NTRS2004

Ulysses Observations of the Magnetic Connectivity between CMEs and the Sun

We have investigated the magnetic connectivity of coronal mass ejections (CMEs) to the Sun using Ulysses observations of suprathermal electrons at various distances between 1 AU and 5.2 AU. Drawing on ideas concerning the eruption and evolution of CMEs, we had anticipated that there might be a tendency for CMEs to contain progressively more open field lines, as reconnection back at the Sun either opened or completely disconnected previously closed field lines threading the CMEs. Our results, however, did not yield any discernible trend. By combining the potential contribution of CMEs to the heliospheric flux with the observed build-up of flux during the course of the solar cycle we also derive a lower limit for the reconnection rate of CMEs that is sufficient to avoid the "flux catastrophe" paradox. This rate is well below our threshold of detectability.

Riley, Pete↗
NASA NTRS2005

Safety Ellipse Motion with Coarse Sun Angle Optimization

The Hubble Space Telescope Robotic Servicing and De-orbit Mission (HRSDM) was t o be performed by the unmanned Hubble Robotic Vehicle (HRV) consisting of a Deorbit Module (DM), responsible for the ultimate disposal of Hubble Space Telescope (HST) at the end of science operations, and an Ejection Module (EM), responsible for robotically servicing the HST to extend its useful operational lifetime. HRSDM consisted of eight distinct phases, including: launch, pursuit, proximity operations, capture, servicing, EM jettison and disposal, science operations, and deorbit. The scope of this paper is limited to the Proximity Operations phase of HRSDM. It introduces a relative motion strategy useful for Autonomous Rendezvous and Docking (AR&D) or Formation Flying missions where safe circumnavigation trajectories, or close proximity operations (tens or hundreds of meters) are required for extended periods of time. Parameters and algorithms used to model the relative motion of HRV with respect to HST during the Proximity Operations phase of the HRSDM are described. Specifically, the Safety Ellipse (SE) concept, convenient parameters for describing SE motion, and a concept for initializing SE motion around a target vehicle to coarsely optimize sun and relative navigation sensor angles are presented. The effects of solar incidence angle variations on sun angle optimization, and the effects of orbital perturbations and navigation uncertainty on long term SE motion are discussed.

Naasz, Bo↗
NASA NTRS2006

The Mysterious Origins of Solar Flares: New observations are beginning to reveal what triggers these hughes explosions of the sun's atmosphere

Solar flares can release the energy equivalent of billions of atomic bombs in the span of just a few minutes. These explosions give off a burst of x-rays and charged particles, some of which may later hit Earth, endangering satellites and causing power outages. The sun's tumultuous magnetic fields provide the fuel of flares. The sudden release of energy in a flare results from a process called reconnection, whereby oppositely directed magnetic field lines come together and partially annihilate each other. Although theoretical studies of magnetic reconnection on the sun have been carried out for decades, only recently have space probes uncovered observational evidence for this phenomenon. The telltale signs include pointed magnetic loops located below the spot where magnetic reconnection is taking place.

Holman, Gordon D.↗