High‐voltage polar‐orbit and beam‐induced charging of a dielectric spacecraft: A wake‐induced barrier effect mechanism

We propose a mechanism which permits high‐voltage auroral zone charging to occur on a large enough mostly dielectric spacecraft, in situations where one would otherwise expect such charging to be suppressed by secondary‐electron or photoelectron escape from exposed surfaces. This extends, to lower equivalent temperatures, the range of auroral electron plasma conditions in which one can expect such a spacecraft to undergo high‐voltage charging. It should also permit such charging to occur in sunlight. Our results yield a tentative prediction that the Shuttle Orbiter is a large enough spacecraft for such charging, if one adopts the usual definition of “high‐voltage” charging as involving surface potentials at least 100 V different from space potential. The mechanism involves the suppression of electron emission by a potential barrier in the spacecraft wake. In contrast with barrier effect charging in geosynchronous orbit conditions, (1) this barrier is produced by unbalanced electron space charge and not by the presence of surfaces at larger negative potentials elsewhere on the spacecraft, (2) instead of limiting differential charging, this barrier produces it, and (3) instead of a saddle point, the potential distribution involves a minimum which migrates toward the spacecraft and almost reaches it as the spacecraft charges toward a steady state. We also apply this mechanism to propose an explanation for features of Shuttle Orbiter charging observed during the SEPAC (Space Experiments With Particle Accelerators) Spacelab 1 electron beam experiment.