Deep Space One investigations of ion propulsion plasma environment

Deep Space One (DSI) is the first interplanetary spacecraft operated on sol ar electric propulsion. One of the primary investigations of DSI is to char acterize ion propulsion-induced plasma interactions and their effects on sp acecraft and solar wind measurements based on two plasma diagnostic package s. The first in situ measurements of an ion propulsion-induced plasma envir onment obtained from an interplanetary spacecraft are reported. Analysis of the measurements reveals interesting correlations between the induced char ge-exchange plasma environment and thruster operating conditions. Sensors n ear the thruster exit measured charge-exchange ions with a number density o f similar to 10(6) cm(-3) and a current density of similar to 10(-7) A/cm(- 2) under typical thruster operating conditions, a result in good agreement with preflight predictions based on computer particle simulations. Observat ions on the opposite side from the thruster suggest that the dominant facto r for charge-exchange ion backflow is the potential distribution surroundin g the spacecraft rather than the charge-exchange ion production rate.