Calculation of escape currents of electrons emitted from negatively charged spacecraft surfaces in a magnetic field

Details Calculation of escape currents of electrons emitted from negatively charged spacecraft surfaces in a magnetic field Calculation of escape currents of electrons emitted from negatively charged spacecraft surfaces in a magnetic field

Mar 1988

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1988jgr....93.1933l&link_type=abstract

Journal of Geophysical Research, Volume 93, Issue A3, p. 1933-1943

Physics

Plasma Physics

11

Space Plasma Physics: Spacecraft Sheaths, Wakes, Charging, Space Plasma Physics: Charged Particle Motion And Acceleration, Ionosphere: Auroral Ionosphere

Scientific paper

In low Earth orbit, the geomagnetic field B is strong enough that secondary electrons or photoelectrons emitted from spacecraft surfaces have an average gyroradius much smaller than typical dimensions of large spacecraft. This implies that escape of these electrons will be strongly inhibited on surfaces which are nearly parallel to B, even if a repelling electric field exists outside them. This effect is likely to make an important contribution to the current balance and hence the equilibrium potential of such surfaces, making high-voltage charging of them more likely. We present numerically-calculated escaping electron fluxes for these conditions, based on the approximations of uniform fields and Maxwellian emission-velocity distributions. We also present an analytic curve-fit to the results for the important case of normal electric field (uniformly-charged surfaces). For strong normal electric fields, escape is effectively suppressed only when a surface is parallel to B within a few degrees or less, and this leads to ``sensitivity effects'' in attempts to predict auroral-zone spacecraft charging. A nonzero tangential component in the surface electric field can greatly enlarge the range of surface orientations for which excape is suppressed, and can also produce large surface currents. We also propose a simple approximate method for calculating the space-charge-density distribution of escaping electrons. Our results imply that on a mostly dielectric large spacecraft such as a Shuttle, local charging, especially on surfaces nearly parallel to B, may occur in ionospheric conditions which do not produce overall charging.

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