Solar and Space Physics Space Science in the Twenty-First Century -- Imperatives for the Decades 1995 to 2015 (1988) / Chapter Skim
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4. New Initiatives: 1995 to 2015
4. New Initiatives: 1995 to 2015
Pages 33-53
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From page 33... ...
SOLAR AND HE[IO SPHERIC PHYSICS Local Measurements in the Solar Atmosphere At present, our understanding of the origin of the solar wind is based entirely on theory and remote sensing. Direct measurements of the solar wind plasma, the interplanetary magnetic field, the energetic particle population, and associated wave-particle interactions are available, but only at distances greater than the 0.3 AU perihelion distances of Helios ~ and 2.
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From page 34... ...
A perihelion distance of 4 solar radii is anticipated, with a local wind speed of about 50 km/s, electron and ion plasma temperatures of about 106K, and plasma density and magnetic field strength of less than 106 electrons/cm3 and 105 gamma, respectively. A drawing of the Solar Probe trajectory is shown in Figure 4.1.
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From page 35... ...
characterization of coronal streamers, the place of origin and the boundaries of high-speed and low-speed flows close to the Sun, the extent of heavy element fractionation and elemental abundance variations, and the scale sizes of inhomogeneities and the development of the magnetohydrodynamic turbulence that characterizes the solar wind near ~ AU and beyond. The Solar Probe mission can also study the solar spin down rate through measurements of solar wind angular momentum flux.
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From page 36... ...
Coronal holes, one of the sources of high-speed solar wind, are expected to produce quasi-steady high-speed flows over the solar poles during much of the solar cycle, whereas at low latitudes interacting high- and low-speed flows predominate. To understand heliospheric conditions at low solar latitudes has required numerous missions, e.g., Explorers, Pioneers, Mariners, and Voyagers.
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From page 37... ...
The SPO spacecraft should carry a full complement of plasma, energetic particle, magnetic field, and radio wave instruments, similar to what is to be flown on ISPM. In addition, SPO should have pointing capability, through the use of a despun platform on a spinning spacecraft, or as a three-axis stabilized spacecraft, for detailed solar observations using a coronagraph, x-ray telescope, and similar photon observing instruments.
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From page 38... ...
Outer Coronal Physics The Heliosynchronous Orbiter (HSO) , as described in the ESA document Horizon 2000, is an instrumented probe orbiting the Sun at about 30 solar radii with a 26-day period, synchronous with the rotation of the Sun (see Figure 4.3~.
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From page 39... ...
In addition) , simultaneous observations at different positions inside the heliosphere provide three-dimensional snapshots of the magnetic field and the solar wind, important oh servations that will give new insight into the mechanisms that govern the wind generation, acceleration, and propagation.
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From page 40... ...
The 1-AU spacecraft near Earth could be at Ll; the Space Station could service an Ll platform essentially as well as a geosynchronous one. Additional Solar and Helio~heric Studies There is now a considerable body of evidence to suggest that all scales of structure on the Sun, as well as other astrophysically interesting objects, are ultimately governed by small-scale processes associated with interrn~ttent magnetic fields and turbulent stresses.
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From page 41... ...
Several possible schemes, including Jupiter gravity assist and swingby of the Sun at 4 solar radii (see Figure 4.4) as well as use of megawatt nuclear electric propulsion, could provide the necessary acceleration for spacecraft velocities varying from about 50 to 100 km/s (11 to 21 AU/yr)
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From page 42... ...
Key measurements to be made include magnetic field, plasma properties (density, velocity, temperature, composition, plasma waves) , and electric field.
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From page 43... ...
Atmospheric density, temperature, and composition should be measured, along with charged particles and magnetic fields. Surface temperature and composition should also be observed.
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From page 44... ...
by observing energetic neutrals produced by charge exchange. Plasmas et Interactions Cosmic plasmas are often "dusty," by which it is meant that they contain solid particles, some of which are very small dust grains.
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From page 45... ...
Several technology advances will be needed to study plasmadust interactions. These include methods for manufacturing dust with the desired properties; methods for injecting dust clouds with the desired space, velocity, and charge distributions; methods for measuring the velocity, ma - , and charge distributions of dust particles; and methods for the remote sensing of dust clouds.
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From page 46... ...
Ejections of Plasma Waves and Particle Beame All astrophysical plasma systems stellar coronae and winds, planetary magnetospheres, interstellar media—support plasma waves and nonthermal particle beam. The frequencies of the plasma waves range from the Alfven (hydromagnetic)
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From page 47... ...
The physical interpretation of the plasma waves and nonthermal particle beamm measured by spacecraft in situ in solar shy tem plasmas requires thorough diagnostics of the existing plasma environment. interpretations of the electromagnetic plasma radiations measured from remote astrophysical sources rely heavily upon the physical understanding achieved from detailed studies of solar system plasmas.
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From page 48... ...
Large numerical models of the general circulation, energetice, and chemistry of the thermosphere, mesosphere, and ionosphere will be used in the analysis and interpretation of data. Space Station Atmospheric Studies The Space Station and the co-orbiting and polar-orbiting platform~ provide opportunities for extensive probing of the upper atmosphere and ionosphere.
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From page 49... ...
Global Current Minions In a laboratory plasma the electric and magnetic fields are usually generated by circuits external to the plasma. A space plasma differs from a laboratory plasma in that the magnetic and electric fields and currents in the space plasma are self-consistently determined by the Attribution of charged particles in the plasma.
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From page 50... ...
PLANETARY SCIENCE Mare's Aeronomy and Magnetosphere At present we have explored the solar wind interaction with each of the planets out to Saturn, with the single exception of Mars. Thus, the magnitude of any intrinsic martian magnetic field remains uncertain, and the nature of the solar wind interaction is not known because the solar wind could be deflected by either a weak planetary magnetic field or the planetary ionosphere.
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From page 51... ...
Comparative studies of Mercury's magnetosphere are crucial to understanding the role of the terrestrial ionosphere in magnetospheric processes and to bridging the gap between the solar wind interaction with the Moon, which has weak, localizes] magnetization and has no atmosphere, and with the Earth, which has a strong magnetic field.
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From page 52... ...
Furthermore, no direct information is available on the chemistry, energetics, and dynamics of the ionosphere and upper atmosphere. Meaningful advances in understanding the chemical and physical processes in a hydrogen/hydrocarbon-dominated upper atmosphere have to await such measurements.
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From page 53... ...
SUMMARY OF TECHNOLOGY DEVELOPMENT NEEDS The technology development needs identified by this task group can be summarized as follows: . Low-thrust propulsion (Solar Probe, Solar Polar Orbiter, Heliosynchronous Spacecraft, possibly Interstellar Probe)
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