C.9.6 Secondary powered discharge

C.9.6.1. General

Electrostatic discharges can become sustained by being fed from power sources on the spacecraft. This leads to an important additional damage mechanism since the power source can become permanently short-circuited. Systems affected include high power solar arrays and motors such as those which drive solar arrays.

C.9.6.2. Primary discharge

The discharge which is called “primary discharge” is the initial phenomenon that leads to an arc by creating a temporary conductive path (generally it is an expanding plasma bubble) instead of vacuum between two electrodes (polarized conductive parts).

C.9.6.3. Secondary arc

The arc which leads to the term “secondary arcing” is the resulting phenomenon; the current which passes through the conductive path created by the primary discharge.

This secondary arc is powered by an external source (for instance an illuminated solar array). Each time a primary discharge occurs where a secondary arc can occur, this secondary arc forms (a current flow through the temporary conductive path). The secondary arc may have several possible forms:

• A non-sustained arc is a secondary arc that lasts only during the primary discharge including the flash-over. It extinguish when the primary discharge stops.

• A self sustained arc is a secondary arc that lasts longer than the primary discharge.

• A temporary self sustained arc is self sustained but it stops by itself even though the external power is still available.

• A permanent self sustained arc is an arc that does not stop while the external power is available. A possible outcome of this type of arc, if the external power is not quickly removed is that the intense current heat in the vicinity of the secondary arc creates a very highly conductive path by pyrolizing materials around the discharge site. When this conductive path is created, power is diverted from the arc and the arcing site cools. A stable permanent short circuit may remain through the pyrolized material.