Satellite charge control with lithium ion source and electron emission

Abstract

A lithium ion source using thermal emission from a Beta-eucryptite structure has been investigated as a possible control device for spacecraft charging. This source can be used for control of positively charged spacecraft potentials in sunlight and differentially charged spacecraft surfaces in shadow. This thesis investigates the emission characteristics of lithium ion sources in conjunction with two kinds of electron sources and simulates spacecraft charge control. A 0.6-in. lithium ion source produced currents up to 33 micro Amps at a bias voltage of 100 V on the surface (strips) of the simulation body with extraction potentials of 200 V to the screen. Differential charging simulations produced currents up to 21 micro Amps on the rear strip of the simulation structure at a bias voltage of 250 V. A directly heated tungsten dispenser cathode and filament-type electron source were used to overcome space charge limiting effects. Space charge effects were studied with a 0.25-in. lithium ion source in conjunction with the tungsten dispenser cathode. The average increase in current was approximately 50%. Larger increases were found with the 0.6 in. lithium ion source, using the filament electron source. The greatest effects occurred for low extraction voltages (some what 20V). A typical increase was 400 % at 10 V. The vacuum chamber system and geometries for the simulation and investigation were very simple. However, the combined ion and electron sources could be used as a device for controlling a spacecraft potential in geosynchronous orbit.