Ion-thruster propellant utilization.

Maximum propellant utilization in a mercury electron-bombardment thrustor is evaluated. The primary-electron region in the ion chamber of a bombardment thrustor is analyzed at maximum utilization. Both the analysis and experimental data from a range of ion-chamber configurations show a nearly constant loss rate for un-ionized propellant at maximum utilization over a wide range of total propellant flow rate. The discharge loss level of 1000 eV/ion was used to define maximum utilization. The exact level of this definition has no effect on the qualitative results and little effect on the quantitative results. The results obtained are particularly significant whenever efficient throttled operation is required.