In this question, there is discussion of charge buildup on a spacecraft.
Is it possible for a spacecraft to measure its own charge?
Space Exploration Stack Exchange is a question and answer site for spacecraft operators, scientists, engineers, and enthusiasts. It only takes a minute to sign up.Sign up to join this community
The ISS has a device called the Floating Potential Measurement Unit that handles this task. The linked page has a link to a pdf that describes it in more detail.