Differential Charging in LEO, GEO, and Vacuum Chamber
Boris Vayner
Ohio Aerospace Institute and NASA/GRC
I graduated from Rostov State University in 1972 with MS in Theoretical Physics. In 1978 I received PhD in Astrophysics from Tartu University (Estonia), and in 1991 - ScD degree in Astrophysics and Radioastronomy from Moscow State University. Since 1994 I am working at NASA Glenn Research Center performing theoretical and experimental research in the field of spacecraft environmental interactions.
Abstract
Significant differential charging in LEO is caused by collection of electrons on part of solar array with positive potentials with respect to ambient plasma. Physically different mechanism of differential charging is... [ view full abstract ]
Significant differential charging in LEO is caused by collection of electrons on part of solar array with positive potentials with respect to ambient plasma. Physically different mechanism of differential charging is responsible for generation of strong electric field between coverglass and conductor in GEO. Both situations can be simulated in vacuum chamber but with considerable limitations. For example, LEO plasma consists of electrons and oxygen ions while simulated plasma contains electrons and xenon ions. Ion flux to spacecraft surface is determined by its orbital speed but ion flux in chamber depends on plasma source design-and these fluxes can differ by factor 2-4. Differential charging in GEO is caused by energetic electrons with temperatures of 5-20 keV and Maxwellian distribution function. Simulation of GEO differential charging in vacuum chamber is achieved by deploying practically monoenergetic electron beam with energy of 5-10 keV. Inverse gradient differential charging in the experiment is usually created by biasing underlying conductor to some negative potential and irradiating dielectric surface with electron beam of high energy. Typical numbers are the following: bias voltage of 5 kV negative, beam energy of 5.6-5.8 keV, and beam current density within the wide range of 0.1-10 nA/cm2. Steady state charging (zero net current) is reached when the energy of electrons at the dielectric surface is equal to the energy of second crossover(about 2 keV for glass ). For these particular numbers it means surface potential of 3.6-3.8 kV negative, and differential potential of 1.2-1.4 kV. These high potential differences my result in discharges (arcs) located on conductive surfaces (interconnectors or/and cell edges). Arcs may have detrimental effects on spacecraft operation such as power disruption, electromagnetic interference, and solar array output power degradation. Ground tests allow determining possible arc sites, voltage thresholds, current pulse wave forms, and solar cell efficiency degradation. Special actions can be offered to prevent arcing and then test prevention methods before implementing them on real spacecraft.
Authors
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Boris Vayner
(Ohio Aerospace Institute and NASA/GRC)
Topic Areas
Testing / Mitigation , Plasma , Spacecraft Charging
Session
Session 5c » Testing and Mitigation (15:10 - Tuesday, 16th May)
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