Cislunar passive potential sensing through nonmonotonic sheath and ion wake barriers

Knowledge of a neighboring spacecraft's potential in lunar orbit is critical for avoiding arc discharges during docking, accounting for electrostatic forces and torques, and evaluating lunar dust contamination risks. A servicing spacecraft can passively sense a target spacecraft's potential by measuring energies of naturally emitted electrons from the target. While this method has been explored for geosynchronous and cislunar applications, the effects of spacecraft ion wakes and nonmonotonic sheath formations have not been examined. These phenomena can create potential barriers that block emitted electrons, limiting the sensing signal. Barriers arise when the spacecraft width exceeds roughly half the electron Debye length. Wake-induced barriers persist for positive potentials while sheath-induced barriers persist for negative potentials. Large targets that generate such barriers produce lower detected current densities than smaller spacecraft under similar conditions. However, a positively charged servicer can still attract electrons, yielding a reduced but usable signal. The greatest limitation occurs when a target is in the wake of a highly positive servicer, leading to a highly negative target that repels ambient electrons and suppresses emissions. Mitigation strategies include avoiding this configuration or reducing the servicer's potential to shrink the wake.