Corona discharge phenomenon is an important consideration when qualifying powered Orbital Replacement Units of the International Space Station U.S. Laboratory and Airlock elements as electromagnetically compatible. Corona degrades insulating materials and may cause electromagnetic interference. Therefore, it is desirable that powered Orbital Replacement Units do not produce corona discharge regardless of electrode configuration or ambient on-orbit conditions.
For the purpose of space station electromagnetic compatibility verification, determining whether corona will occur is accomplished by comparing the corona onset voltage to the Orbital Replacement Unit operating voltage for a given set of system operating parameters. At the corona onset voltage, the potential exceeds the minimum value needed to produce a self-sustaining ionization process. Corona may result if the operating voltage exceeds this threshold voltage.
To determine corona onset voltages for cathode-present configurations, empirical data is taken from the literature, and Paschen’s Law is used to approximate corona onset theoretically. For cathode-remote configurations, a computer model for burst pulse and continuous streamer inception is adapted. Dr. V. Schroeder developed this model to predict corona discharge formation on raindrops.
Given space station on-orbit conditions and conductor design requirements, corona discharge is not expected to occur on Orbital Replacement Units of the U.S. Laboratory and Airlock. The lowest corona onset voltage found for cathode-present configurations is ≈ 350 VD.C., while burst pulse initiation for cathode-remote configurations is not expected to occur for voltages lower than ≈ 700 VD.C. The operating voltages, including possible transients, of Orbital Replacement Units aboard the U.S. Laboratory and Airlock do not exceed these values.