Bimetallic Compatible Couples
In the construction of a satellite, two metals that form a compatible couple may have to be placed in close proximity to one another. Although this may not cause anomalies or malfunctions in the space environment, it has to be borne in mind that equipment on board the manned habitats of the International Space Station experience humidity levels are up to 70% RH and also that spacecraft and equipment often have to be stored on earth for considerable periods of time and that during storage they may inadvertently be exposed to environments where galvanic corrosion can take place. In fact, this is known to have taken place on several occasions and it is for this reason that the European Space Agency has been studying the dangers involved.

The galvanic corrosion table given in ECSS-Q-70-71 distinguishes four levels.
Level 0 means that the combination can be used at all times, also in immersion in salt water.
Level 1 means that the combination can be used in a non-controlled environment such as assembly area or workshop but not in immersion
Level 2 means that the combination can only be used in a clean room environment, but not outside this area, unless adequately protected
Level 3 means that this combination can not be used unless specific measures to avoid galvanic corrosion are taken.