6.3.1 Grounding of surface metallic parts

a. All structural and mechanical parts shall be electrically bonded to each other, ensuring that, in order to control differential charging, there is a resistance of less than 10⁶ W at each bond.

NOTE 1 For example, for electrical boxes.

NOTE 2 EMC requirements can be more restrictive than this.
For EMC requirements, see ECSS-E-ST-20-07.

b. Ground shall be carried across an articulating joint or hinge using a ground strap.

c. Where structural ground is carried across slip-rings on a rotating joint, at least two slip-rings shall be dedicated to the structural ground path, some at each end of the slip-ring set.

NOTE This is to provide redundancy.

d. Floating surface conductors shall not be used unless they are less than 1 cm² and 10 pF and not part of a multi-conductor elements structure.

NOTE Multi-conductor structures exist where at least two conductive elements are separated by a dielectric surface of less than 100 cm².

e. A risk assessment of the potential discharges due to sharp edges and tips shall be performed

f. Circuits and conductive elements shall remain grounded in all possible situations

NOTE E.g. contacts and cables in switched circuits and moveable conductors.

g. The grounding of surface conductors shall be implemented in one of the following two ways:

¾ Make the grounding to the main spacecraft of external and internal metallic parts and intrinsically conductive parts (like carbon) by a resistance as defined in ECSS-E-ST-20 clause 6.6.3a.

¾ Select the resistance to spacecraft ground not to be exceeded, such that it ensures that metal parts do not float by over V_MAX absolute potential with respect to spacecraft ground.

NOTE This normally leads to a requirement that the product of the resistance R and the area exposed to the environment A, is such that

For a V_MAX of 100 V and J = 10 nA cm^-2,
W m²

For example:

• For a one square metre MLI, the maximum resistance is 5 MW

• For a scientific mission where V_MAX=10 V, W m²