a. Contamination due to neutral and charged particles shall be below a level defined by the customer.
NOTE Acceptable levels of contamination vary and are established on a case by case basis. Optical surfaces and thermal control surfaces can have lower acceptable levels than other surfaces.
b. The level of contamination due to the contaminants shall be assessed through simulation or testing.
NOTE 1 A fraction of the neutral atoms that exit EP systems return to the spacecraft after ionization. These atoms include propellant and material eroded from the thruster itself (e.g. atoms from electrostatic grids).
NOTE 2 Propellant for thrusters and neutralizers and the materials used to construct the thrusters are selected with their effects as contaminants in mind. The use of noble gasses as propellant and neutralizer medium is a typical practice partly for this reason. An issue to be considered is the type of atoms emitted from the EP system and their spatial distribution.