Internal charging (for example, see [19]) refers to the build-up of electric charge, due to particles from the external space environment, anywhere within the spacecraft structure except on its surface. In many cases, this occurs inside dielectrics and is often called deep-dielectric charging. However, internal charging can also occur on electrically isolated conductors within the spacecraft. As with surface charging, this is principally a hazard when high electric fields lead to electrostatic discharge.
As is shown schematically in
Figure C-5, electrons from the external environment can be substantially
attenuated by spacecraft radiation shielding, if present, before a portion is
stopped within a dielectric to produce a current of deposited charge, Jdeposited. This current
leads to an accumulation of charge in the material. This gradually builds up an
electric field between the area of deposition and the ground plane. This
electric field drives a conducted current,
Jconducted, which can be calculated from Ohm’s Law, i.e. 
. Here E is the
electric field and 
is the conductivity.
The conducted current is initially small but eventually an equilibrium is established
in which the conducted current equals the deposited current, i.e. 
. This equilibrium electric field is the maximum i.e.
worst-case achievable by the structure in that environment. The magnitude of
the equilibrium field depends on both the amount of deposited current and on
the conductivity which can be non-uniform throughout the material.
Figure C-5: Schematic diagram of internal charging in a planar dielectric