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NASA NTRS2013

Science Opportunity Analyzer (SOA) Version 8

SOA allows scientists to plan spacecraft observations. It facilitates the identification of geometrically interesting times in a spacecraft s orbit that a user can use to plan observations or instrument-driven spacecraft maneuvers. These observations can then be visualized multiple ways in both two- and three-dimensional views. When observations have been optimized within a spacecraft's flight rules, the resulting plans can be output for use by other JPL uplink tools. Now in its eighth major version, SOA improves on these capabilities in a modern and integrated fashion. SOA consists of five major functions: Opportunity Search, Visualization, Observation Design, Constraint Checking, and Data Output. Opportunity Search is a GUI-driven interface to existing search engines that can be used to identify times when a spacecraft is in a specific geometrical relationship with other bodies in the solar system. This function can be used for advanced mission planning as well as for making last-minute adjustments to mission sequences in response to trajectory modifications. Visualization is a key aspect of SOA. The user can view observation opportunities in either a 3D representation or as a 2D map projection. Observation Design allows the user to orient the spacecraft and visualize the projection of the instrument field of view for that orientation using the same views as Opportunity Search. Constraint Checking is provided to validate various geometrical and physical aspects of an observation design. The user has the ability to easily create custom rules or to use official project-generated flight rules. This capability may also allow scientists to easily assess the cost to science if flight rule changes occur. Data Output allows the user to compute ancillary data related to an observation or to a given position of the spacecraft along its trajectory. The data can be saved as a tab-delimited text file or viewed as a graph. SOA combines science planning functionality unique to both JPL and the sponsoring spacecraft. SOA is able to ingest JPL SPICE Kernels that are used to drive the tool and its computations. A Percy search engine is then included that identifies interesting time periods for the user to build observations. When observations are then built, flight-like orientation algorithms replicate spacecraft dynamics to closely simulate the flight spacecraft s dynamics. SOA v8 represents large steps forward from SOA v7 in terms of quality, reliability, maintainability, efficiency, and user experience. A tailored agile development environment has been built around SOA that provides automated unit testing, continuous build and integration, a consolidated Web-based code and documentation storage environment, modern Java enhancements, and a focus on usability

Witoff, Robert J.↗
NASA NTRS1999

Kelvin Helmholtz Instability at the Equatorial Magnetotail Boundary: MHD Simulation and Comparison with Geotail Observations

On March 24, 1995 the Geotail spacecraft observed large fluctuations of the magnetic field and plasma properties in the Low Latitude Boundary Layer (LLBL) about 15 R(sub E) tailward of the dusk meridian. Although the magnetospheric and the magnetosheath field were strongly northward, the B(sub z) component showed strong short duration fluctuations in which B(sub z) could even reach negative values. We have used two-dimensional magnetohydrodynamic simulations with magnetospheric and magnetosheath input parameters specifically chosen for this. Geotail event to identify the processes which cause the observed boundary properties. It is shown that these fluctuations can be explained by the Kelvin-Helmholtz instability if the k vector of the instability has a component along the magnetic field direction. The simulation results show many of the characteristic properties of the Geotail observations. In particular, the quasi-periodic strong fluctuations are well explained by satellite crossings through the Kelvin-Helmholtz vortices. It is illustrated how the interior structure of the Kelvin-Helmholtz vortices leads to the rapid fluctuations in the Geotail observations. Our results suggest an average Kelvin-Helmholtz wavelength of about 5 R(sub E) with a vortex size of close to 2 R(sub E) for an average repetition time of 2.5 minutes. The growth time for these waves implies a source region of about 10 to 16 R(sub E) upstream from the location of the Geotail spacecraft (i.e., near the dusk meridian). The results also indicate a considerable mass transport of magnetosheath material into the magnetosphere by magnetic reconnection in the Kelvin-Helmholtz vortices.

Fairfield, Donald H.↗
NASA NTRS1998

Radio Emissions Observed by Galileo near Io

The Galileo spacecraft observed spin modulation of radio wave emissions near Io in the frequency range from about 600 kHz to about 1.2 MHz. Assuming transverse EM radiation, we have used the modulation of the high-frequency sweep-frequency receiver signals of the electric dipole antenna over many spins to estimate the plane through the source. The emission has a range of frequencies close to the local upper hybrid frequency of the plasma near Io. We conclude that the emission may be associated with either the plasma torus or magnetic flux tubes in the wake of Io (the Alfven current system). We postulate this emission may be associated with a free-energy source such as density gradients, energetic plasma beams and/or an electron distribution with a temperature anisotropy. All of these free-energy sources are observed or expected in the torus near Io. The observations are the first in the hectometric frequency range that have a source associated with Io or in the Io torus.

Menietti, J. D.↗
NASA NTRS1986

Solar radio emission

For this review, a selection has been made of a number of topics which are current active areas of both observational and theoretical research. Observations of Type III bursts are examined, taking into account ground-based observations (above approximately 8 MHz), spacecraft observations (below 1 MHz), and Langmuir waves and electron streams. Microwave bursts are considered along with Type II bursts, moving Type IV bursts, and Type I noise storms. The theory of Type III radio bursts (radio emission from electron streams) is discussed, giving attention to quasi-linear theory, induced scatter of ions, wave-wave effects of the nonlinear refractive and self-focusing variety, the second harmonic emission from Langmuir waves, fundamental emission from Langmuir waves, and density irregularities and ion-acoustic waves. Aspects of radio emission from shock waves and current sheets are also studied.

Goldman, M. V.↗
NASA NTRS1987

Evolution of the solar wind structure in the outer heliosphere

Shocks and interaction regions play very important roles in the evolution of large-scale solar wind structure in the outer heliosphere. This study is based on (1) plasma and magnetic field data observed from Voyager and Pioneer spacecraft, and (2) a quantitative magnetohydrodynamic simulation model. Interaction regions bounded by a forward and a reverse shock begin to form near 1 AU at the leading edges of a large-scale stream. The total pressure in the region is greater than the ambient pressure by a factor of ten or more. Large jumps in pressure remain as a prominant feature of the interplanetary structure even as the jumps in flow speed become less visible in the outer heliosphere. The propagation of the forward and reverse shocks widens the dimension of an interaction region. As a result, two interaction regions belonging to neighboring streams coalesce to form a merged interaction region (MIR). Collision and merging of shocks take place during the coalescence process. Two MIRs can themselves merge again at greater heliocentric distances. Simulation results agree well with spacecraft observations, and they explain major restructuring of the solar wind in the outer heliosphere.

Whang, Y. C.↗
NASA NTRS1992

Technical needs and research opportunities provided by projected aeronautical and space systems

The overall goal of the present task is to identify the enabling and supporting technologies for projected aeronautical and space systems. A detailed examination was made of the technical needs in the structures, dynamics and materials areas required for the realization of these systems. Also, the level of integration required with other disciplines was identified. The aeronautical systems considered cover the broad spectrum of rotorcraft; subsonic, supersonic and hypersonic aircraft; extremely high-altitude aircraft; and transatmospheric vehicles. The space systems considered include space transportation systems; spacecrafts for near-earth observation; spacecrafts for planetary and solar exploration; and large space systems. A monograph is being compiled which summarizes the results of this study. The different chapters of the monograph are being written by leading experts from governmental laboratories, industry and universities.

Noor, Ahmed K.↗
NASA NTRS1996

A matched filter method for ground-based sub-noise detection of terrestrial extrasolar planets in eclipsing binaries: application to CM Draconis

The photometric detection of extrasolar planets by transits in eclipsing binary systems can be significantly improved by cross-correlating the observational light curves with synthetic models of possible planetary transit features, essentially a matched filter approach. We demonstrate the utility and application of this transit detection algorithm for ground-based detections of terrestrial-sized (Earth-to-Neptune radii) extrasolar planets in the dwarf M-star eclipsing binary system CM Draconis. Preliminary photometric observational data of this system demonstrate that the observational noise is well characterized as white and Gaussian at the observational time steps required for precision photometric measurements. Depending on planet formation scenarios, terrestrial-sized planets may form quite close to this low-luminosity system. We demonstrate, for example, that planets as small as 1.4 Earth radii with periods on the order of a few months in the CM Draconis system could be detected at the 99.9% confidence level in less than a year using 1-m class telescopes from the ground. This result contradicts commonly held assumptions limiting present ground-based efforts to, at best, detections of gas giant planets after several years of observation. This method can be readily extended to a number of other larger star systems with the utilization of larger telescopes and longer observing times. Its extension to spacecraft observations should also allow the determination of the presence of terrestrial-sized planets in nearly 100 other known eclipsing binary systems.

NASA Discipline Number 52-10↗
NASA NTRS2010

Impact of Magnetic Draping, Convection, and Field Line Tying on Magnetopause Reconnection Under Northward IMF

We simulate a northward IMF cusp reconnection event at the magnetopause using the OpenGGCM resistive MHD code. The ACE input data, solar wind parameters, and dipole tilt belong to a 2002 reconnection event observed by IMAGE and Cluster. Based on a fully three-dimensional skeleton separators, nulls, and parallel electric fields, we show magnetic draping, convection, ionospheric field line tying play a role in producing a series of locally reconnecting nulls with flux ropes. The flux ropes in the cusp along the global separator line of symmetry. In 2D projection, the flux ropes the appearance of a tearing mode with a series of 'x's' and 'o's' but bearing a kind of 'guide field' that exists only within the magnetopause. The reconnecting field lines in the string of ropes involve IMF and both open and closed Earth magnetic field lines. The observed magnetic geometry reproduces the findings of a superposed epoch impact parameter study derived from the Cluster magnetometer data for the same event. The observed geometry has repercussions for spacecraft observations of cusp reconnection and for the imposed boundary conditions reconnection simulations.

Wendel, Deirdre E.↗
NASA NTRS2022

Dayside Transient Phenomena and Their Impact on the Magnetosphere and Ionosphere

Dayside transients, such as hot flow anomalies, foreshock bubbles, magnetosheath jets, flux transfer events, and surface waves, are frequently observed upstream from the bow shock, in the magnetosheath, and at the magnetopause. They play a significant role in the solar wind-magnetosphere-ionosphere coupling. Foreshock transient phenomena, associated with variations in the solar wind dynamic pressure, deform the magnetopause, and in turn generates field-aligned currents (FACs) connected to the auroral ionosphere. Solar wind dynamic pressure variations and transient phenomena at the dayside magnetopause drive magnetospheric ultra low frequency (ULF) waves, which can play an important role in the dynamics of Earth’s radiation belts. These transient phenomena and their geoeffects have been investigated using coordinated in-situ spacecraft observations, spacecraft-borne imagers, ground-based observations, and numerical simulations. Cluster, THEMIS, Geotail, and MMS multi-mission observations allow us to track the motion and time evolution of transient phenomena at different spatial and temporal scales in detail, whereas ground-based experiments can observe the ionospheric projections of transient magnetopause phenomena such as waves on the magnetopause driven by hot flow anomalies or flux transfer events produced by bursty reconnection across their full longitudinal and latitudinal extent. Magnetohydrodynamics (MHD), hybrid, and particle-in-cell (PIC) simulations are powerful tools to simulate the dayside transient phenomena. This paper provides a comprehensive review of the present understanding of dayside transient phenomena at Earth and other planets, their geoeffects, and outstanding questions.

Bow shock↗
NASA NTRS1990

Numerical simulations of the decay of Martian global dust storms

The decay of Martian global (great) dust storms is investigated. One-dimensional (vertical, static atmosphere) and two-dimensional (latitude-height, steady state circulation) simulations carried out with an aerosol transport-microphysical model indicate that atmospheric motions play a significant role in the observed decay of global dust storms. Spacecraft observations (Mariner 9, Viking) of the 1971 and the two 1977 planet-encircling dust storms have provided suggestions about some characteristics of storm decay. Specifically, the dust particle size distribution is inferred to have remained essentially unchanged for particles with radii between 1 and 10 microns during decay of the 1971 storm, and surface visible opacity declined quasi-exponentially with time in northern midlatitudes during the decay of the two 1977 storms. The results from this investigation indicate that two- and three-dimensional dynamical processes play a significant role the observed decay features of Martian global dust storms. The most important processes are the lofting of dust by vertical motions in the dust source region of the Southern Hemisphere subtropics and a continuing advective resupply of atmospheric dust into the dust sink regions of the Northern Hemisphere. This work has implications for Viking data analyses and future Mars observer observations and requires that the particle size distribution be treated as a time and latitude dependent quantity.

Murphy, James R.↗
NASA NTRS2003

Early Results from the Odyssey THEMIS Investigation

The Thermal Emission Imaging System (THEMIS) began studying the surface and atmosphere of Mars in February, 2002 using thermal infrared (IR) multi-spectral imaging between 6.5 and 15 m, and visible/near-IR images from 450 to 850 nm. The infrared observations continue a long series of spacecraft observations of Mars, including the Mariner 6/7 Infrared Spectrometer, the Mariner 9 Infrared Interferometer Spectrometer (IRIS), the Viking Infrared Thermal Mapper (IRTM) investigations, the Phobos Termoscan, and the Mars Global Surveyor Thermal Emission Spectrometer (MGS TES). The THEMIS investigation's specific objectives are to: (1) determine the mineralogy of localized deposits associated with hydrothermal or sub-aqueous environments, and to identify future landing sites likely to represent these environments; (2) search for thermal anomalies associated with active sub-surface hydrothermal systems; (3) study small-scale geologic processes and landing site characteristics using morphologic and thermophysical properties; (4) investigate polar cap processes at all seasons; and (5) provide a high spatial resolution link to the global hyperspectral mineral mapping from the TES investigation. THEMIS provides substantially higher spatial resolution IR multi-spectral images to complement TES hyperspectral (143-band) global mapping, and regional visible imaging at scales intermediate between the Viking and MGS cameras.

Christensen, Philip R.↗
NASA NTRS1997

Solar disturbances and correlated geospace responses: Relativistic magnetospheric electron acceleration

The role of high-speed solar wind streams in driving relativistic electron acceleration within the earth's magnetosphere is discussed based on International Solar-Terrestrial Physics (ISTP) Observatory and related spacecraft observations. A 'recirculation' mechanism for electron acceleration and redistribution was invoked. Recently, an increase in the number of coronal mass ejections (CMEs) and related 'magnetic clouds' was seen at 1 AU. As these CME/cloud systems interact with the earth's magnetosphere, they are able to produce rapid enhancements in the magnetospheric electron population. The relativistic electron signatures observed by the POLAR, SAMPEX, and other spacecraft during recent magnetic cloud events, especially January 1997 and May 1997, were compared and contrasted. In these cases, there were large solar wind and IMF changes during the cloud passages and very rapid energetic electron acceleration was observed. The relative geoeffectiveness of these events is examined and 'space weather' predicatability is assessed.

Baker, D. N.↗
NASA NTRS1988

Multipoint observations of the magnetopause - Results from ISEE and AMPTE

Multiple spacecraft observations of the magnetopause have made it possible to infer boundary motion and structure, and to compare these with theoretical expectations. the results of the ISEE mission indicate the magnetopause is thicker than expected, often ten magnetosheath ion gyroradii or more, and that its characteristic radial motion is usually sub-Alfvenic. With small spacecraft separations it is possible to infer considerable small-scale magnetic structure within the current layer, suggesting filamentary currents much smaller than an ion gyroradius. Such a microstructure may be important in particle diffusion and, hence, reconnection. There are also phenomena on much larger scales, the highly variable boundary layer, flux transfer events and surface waves due to dynamic pressure variations, the structure of which can be best determined when spacecraft separations are large.

Elphic, R. C.↗
NASA NTRS1995

Limits on Deceleration and Asymmetry of Solar Wind Speed

It has been suggested by Richardson et al. [1995] that the solar wind shows signs of deceleration due to mass-loading by interstellar pickup ions. They based their conclusion on observations from the Voyager 2 and IMP 8 spacecraft. Observations from the Pioneer Venus Orbiter (PVO), Voyager 2, and Pioneer 10 spacecraft are compared to look for this deceleration. While these comparisons suggests the possibility of deceleration at Voyager 2, the magnitude of this deceleration appears to be significantly less than the deceleration reported by Richardson et al. [1995]. Some of this difference could be explained by a north-south asymmetry in solar wind speed. The implications of these results are discussed, along with possibilities for further investigations.

Gazis, P. R.↗
NASA NTRS1977

Interplanetary baseline observations of type III solar radio bursts

Simultaneous observations of type III radio bursts from spacecraft separated by 0.43 AU have been made using the solar orbiters Helios-A and Helios-B. The burst beginning at 19:22 UT on March 28, 1976, has been located from the intersection of the source directions measured at each spacecraft and from burst arrival-time differences. The source positions range from 0.03 AU from the sun at 3000 kHz to 0.08 AU at 585 kHz. The electron density along the burst trajectory and the exciter velocity (0.13c) were determined directly without the need to assume a density model, as has been done with single-spacecraft observations. The separation of Helios-A and -B has also provided measurements of burst directivity at low frequencies. For the March 28 burst the intensity observed from near the source longitude (Helios-B) was 3-10dB greater than that from 60 deg west of the source (Helios-A)

Weber, R. R.↗
NASA NTRS1993

Multiple spacecraft survey of the north-south asymmetry of the interplanetary magnetic field

Spacecraft observations spanning 22 AU of heliocentric distance performed over 23 years have been used to examine the N-S asymmetry of the interplanetary magnetic field. The winding of the Parker spiral both north and south of the heliospheric current sheet as observed by the Pioneer-Venus Orbiter and numerous near-earth spacecraft is examined using the observed sector structure of the solar wind. It is concluded that a significant and persistent asymmetry exists between the two hemispheres at 0.7 and 1 AU.

Smith, Charles W.↗
NASA NTRS1992

Venus surface mineralogy - Observational and theoretical constraints

Earth-based, earth-orbital, and spacecraft observations of the atmosphere and surface of Venus, thermodynamic models of atmosphere-lithosphere interactions, and where available kinetic data on relevant gas-solid reactions to place constraints on the mineralogy of the surface of Venus are used. Which minerals and mineral assemblages are stable on the surface of Venus and which, if any, of these minerals are involved in controlling the abundances of reactive gases in the atmosphere of Venus. It is concluded by identifying key issues facing us today about the mineralogy and geochemistry of the surface of Venus and suggest experimental, observational, and theoretical studies that can improve knowledge of these important questions are discussed.

Fegley, Bruce, Jr.↗
NASA NTRS1990

Study of planetary atmospheres by absorptive occultations

The absorption spectrum of the upper atmosphere can be observed as a function of height as a spacecraft observes the setting or rising of the sun or a star behind the limb of a planet. Data reduction methodology for absorptive occultations are described. Emphasis is placed on occultations by atmospheres other than the earth's in which the observed effects are dominated by absorption. Observations of the other planets by ultraviolet spectrometers able to look at the sun as well as stars are presented. Most of the instruments utilized the extreme ultraviolet wavelength region between 500 and 1600 A, which includes strong absorptions by nearly all gases and is consequently very useful for an initial exploration of a little known atmosphere. A closely related development is the utilization of stellar occultations seen from the earth's surface or airborne platforms, to obtain geometrical information on planets, rings, and asteroids, including density profiles of atmospheres. Voyager instruments defined the upper atmospheres of all four Jovian planets and the satellites Titan and Triton. Tight upper limits on the atmosphere of Mercury were established by Mariner 10.

Smith, Gerald R.↗