An overview of electron and ion beam effects in charging and discharging to spacecraft

The charging and discharging of the SCATHA satellite by means of electro- and ion-beam emissions in the geosynchronous environment were investigated. It was found that during electron beam emissions in sunlight the photoelectrons from nearby surfaces isolated from the satellite body tend to return to the body, thus affecting its potential. It was also found that attempts to discharge a spacecraft by means of electron-beam emission can result in differential charging between dielectric surfaces and spacecraft ground. At low ion-beam currents, the level of spacecraft charging increases as the current increases. Beyond a critical current, the level decreases with a nonmonotonic current-voltage behavior. Abundant neutrals are present in the ion beam. Low-energy ions generated by charge exchange return to the spacecraft and reduce the charging level. It was also shown that discharging by means of low-energy plasma-beam emission is more efficient than using an electron or ion beam alone. This conclusion is important for spacecraft engineers designing automatic discharge systems for future spacecraft. >