a. If the requirements of 6.3.3 and 6.4 are not satisfied, tests in accordance with 6.6.1b shall be performed on a representative sample of the concerned surface material or assembly.
c. The tests shall either:
¾ reproduce the physical process of concern, i.e. charging, in a worst-case environment, or
¾ yield electrostatic material properties enabling the materials response to such an environment to be assessed.
d. The tests shall be performed under vacuum (i.e. < 1 mPa) and electron irradiation.
e. The tests shall be performed after outgassing of the material.
NOTE Changes to material conductivity can occur as volatile substances are lost by outgassing.
f. The effect of dose-rate shall be included via irradiation by electrons that have energy sufficient to pass right through the sample
g. A mono-energetic spectrum with energy from 20 keV to 40 keV shall be used to deliver the surface charging current.
h. The flux intensity shall be 1 nA/cm2 except for LEO where it shall be 10 nA/cm2.
i. For LEO, the current shall be delivered in pulses representative of auroral crossing durations, typically 2 minutes for circular LEO orbits with inclination above 50º.
j. Tests shall be performed at temperature of use in space.
NOTE This is because temperature has a large effect on conductivity in dielectric materials. As temperature falls, resistivity rises.
k. Qualification tests for materials shall:
¾ be performed with multi-energetic electron beams, and
¾ reproduce the dose-rate and charging current of the environment.
NOTE This is because of the radiation and electric field induced conductivity. These effects influence the surface voltage and consequently the risk of discharge.
l. The number of samples to be tested shall be agreed with the customer.
NOTE Because of microscopic differences between samples, several samples are normally tested to allow for sample variability.