NASA Scientific and Technical Aerospace Reports

show too that the Maxwell Boltzmann distribution for the electron is not adapted to model the current flow between spacecraft
and GEO ambient plasma. In a second part, we will present the plasma contactor principle and the physical mechanisms which
generates charges exchange between spacecraft and ambient plasma. We will show that we can compare the physical
mechanisms of the expansion of high-density plasma (the plasma generated by the thruster) into another plasma (the GEO
ambient plasma) with the mechanism appearing in a PN junction. The region of high-density plasma is similar to the N region
(electrons majority) of the junction and the region of low density is similar to the P region (electron minority). So, with this
analogy we can understand how a current flow can circulate between the spacecraft and the ambient plasma through the plasma
of the thruster. Finally, we will present a model for electrons to take account of this current flow and its impact on spacecraft
charging.
Author
Plasmas (Physics); Spacecraft Charging; Electrostatics; Mathematical Models; Thrustors
20040111098 Science Applications International Corp., San Diego, CA, USA
Representation of the Geosynchronous Plasma Environment for Spacecraft Charging Calculations
Davis, V. A.; Mandell, M. J.; Thomsen, M. F.; 8th Spacecraft Charging Technology Conference; March 2004; 9 pp.; In
Afrikaans; See also 20040111031; No Copyright; Avail: CASI; A02, Hardcopy
Historically, our ability to predict and postdict surface charging has suffered from both a lack of reliable secondary
emission and backscattered electron yields and poor characterization of the plasma environment. One difficulty lies in the
common practice of fitting the plasma data to a Maxwellian or Double Maxwellian distribution function, which may not
represent the data well for charging purposes. For 13 years Los Alamos National Laboratory (LANL) has been accumulating
measurements of electron and proton spectra from Magnetospheric Plasma Analyzer (MPA) instruments aboard a series of
geosynchronous satellites. These data provide both a plasma characterization and the potential of the instrument ground. We
use electron and ion flux spectra measured by the LANL MPA to examine how the use of different spectral representations
of the charged particle environment in computations of spacecraft potentials during magnetospheric substorms affects the
accuracy of the results. We calculate the spacecraft potential using both the measured fluxes and several different fits to these
fluxes. These flux measurements and fits have been corrected for the difference between the measured and calculated potential.
The potentials computed using the measured fluxes, the best available material properties of graphite carbon, and a secondary
electron escape fraction of 81%, are within a factor of three of the measured potential for nearly all the data. Using a Kappa
fit to the electron distribution function and a Maxwellian fit to the ion distribution function gives agreement similar to the
calculations using the actual data. Alternative spectral representations, including Maxwellian and double Maxwellian for both
species, lead to less satisfactory agreement between predicted and measured potentials.
Author
Spacecraft Charging; Geosynchronous Orbits; Earth Orbital Environments; Space Plasmas
20040111099 Moscow State Univ., Russia
Computer Simulation of Radiation Charging Processes in Spacecraft Materials
Mileev, Valery; Novikov, L. S.; 8th Spacecraft Charging Technology Conference; March 2004; 6 pp.; In English; See also
20040111031; No Copyright; Avail: CASI; A02, Hardcopy
The problems of application of Monte-Carlo method to modeling of processes of internal charging of spacecrafts
dielectric materials of under impact of electrons with energies 0.1 - 10 MeV, appropriate to range of energy spectrums of the
Earth radiation belts electrons are considered. The dynamic model of internal charging including self-consistent calculation
of internal electrical field and its influence to motion of primary and secondary charged particles is shown. In terms of the
simulation results, the differences between processes of internal charging of dielectrics in space conditions and in laboratory
experiments in electron accelerators are explained.
Author
Monte Carlo Method; Dielectrics; Charged Particles; Radiation Belts; Dynamic Models
20040111103 NASA Glenn Research Center, Cleveland, OH, USA
On-Orbit Daytime Solar Heating Effects: A Comparison of Ground Chamber Arcing Results
Galofaro, J.; Vayner, B.; Ferguson, D.; 8th Spacecraft Charging Technology Conference; March 2004; 9 pp.; In English; See
also 20040111031; No Copyright; Avail: CASI; A02, Hardcopy
The purpose of the current experiment is to make direct comparisons between the arcing results obtained from the
diffusion pumped vertical chamber and our newly renovated Teney vacuum chamber which is equipped with a cryogenic
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