Appendix E

Test Methods

Tests that can be performed to validate some aspects of charging problems are described conceptually below. The focus here is largely on materials with limited descriptions of component, subsystem, and system tests. Details such as test levels, test conditions, instrumentation ranges, bakeout time, and pass/fail criteria should be considered for any tests. Vacuum bakeout/aging of materials before testing is important because apparent surface properties, especially resistivity, quite often increase with aging in space, as adsorbed water and other conductive contaminants depart because of outgasing.

E.1 Electron-Beam Tests

Electron-beam test facilities are to be used to test smaller elements of the spacecraft. This test can be used to determine whether a material sample will arc in a given electron environment and can measure the size of the resulting ESD, if any. Electron-beam tests have the advantage that they are real: The electrons can be accelerated to energies that will penetrate and deposit more or less to the depth desired by the experimenter. They have the disadvantage that the beam is usually monoenergetic rather than a spectrum—the electrons will be deposited initially in a diffuse layer depending on their energy rather than being distributed throughout the exposed material. Usually, the illuminated area is less than 103 cm2 in size. The real area may not be testable, in which case scaling should be applied to the measured results to estimate the ...

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