Control and Monitoring Techniques
Charge control devices are a means of controlling spacecraft potential. Various active charged-particle emitters have been and are being developed and show promise of controlling spacecraft potential in the space plasma environment. At this time, only neutral plasma devices (both ion and electron emitters) have demonstrated the ability to control spacecraft potential in geomagnetic substorms. These devices are sometimes recommended for charge control purposes (1, 2). Plasma contactors are currently the most widely used charge control devices.
Emitted particles constitute an additional term in the current balance of a spacecraft. Because the ambient current densities at geosynchronous altitude are quite small, emitting small currents from a spacecraft can have a strong effect on its potential, as has been demonstrated on ATS-5, ATS-6, SCATHA, and other spacecraft. However, devices that emit particles of only one electric charge (e.g., electrons) are not suitable for active potential control applications unless all spacecraft surfaces are conducting. Activation of such a device will result in a rapid change of spacecraft potential. Differential charging of any insulating surfaces will occur, however, and cause potential barrier formation near the emitter. Emission of low-energy particles can then be suppressed. Higher-energy particles can escape, but their emission could result in the buildup of large ...