Threshold for spacecraft charging in double‐Maxwellian plasma

Charging of geosynchronous satellites has been attracting much attention. The geosynchronous plasma is generally modeled by single‐Maxwellian distribution or better modeled by double‐Maxwellian distribution in disturbed environments. For single‐Maxwellian plasma, the critical temperature has been predicted theoretically for onset of negative surface charging. While for double‐Maxwellian plasma, in which charging determination becomes more complicated, there is not an analogous threshold condition developed so far. In this paper, the threshold condition for onset of negative charging in eclipse is developed theoretically, namely, the spacecraft charging can be triggered when the weighted average of the total averaged yields of secondary and backscattered electron for the two plasmas equals to unity. The threshold condition indicates that both temperatures and density ratio of the two components are decisive to onset of spacecraft charging. The charging behaviors for two typical cases are discussed; it is found that sudden potential jump at the threshold does not always occur, which is different from conventional understandings. Whether the potential jumps abruptly or transits smoothly to negative domain depends on the specific condition. The criterion for potential jump with a short form is acquired theoretically, and it predicts the necessary condition that a sudden potential jump or continuous transition occurs.