Charging characteristics of construction materials of spacecraft irradiated by an electron beam

Abstract

Composite materials like carbon fiber-reinforced plastics (CFRP) or fiber-reinforced plastics (FRP) are used for construction materials of spacecraft. When FRP are used for construction materials of spacecraft, germanium (Ge)-sputtered FRP is used because of its thermal control ability. In an orbit at high altitude, charging of polymer materials can hinder measurements on spacecraft. To investigate the charging of these kinds of materials in a vacuum, electron beams were used to irradiate test pieces of FRP, Ge-sputtered FRP, and CFRP. The experiments were conducted in a high-vacuum chamber with an electron beam gun. The results show that the absolute surface potential of Ge-sputtered FRP remains lower than that of FRP. The irradiation of negatively charged Ge-sputtered FRP decreases the surface potential. Ge-sputtered FRP with a thicker layer of Ge shows a similar and pronounced tendency. Irradiation with higher current density also causes more rapid decrease of the potential. The results for CFRP also show low values of the saturated surface potential. These characteristics are different from those of simple polymer test pieces such as fluoroethylenepropylene (FEP) film. Although the penetration depth of electrons is confined to the Ge layer, the surface potential of Ge-sputtered FRP is lower than the potential expected for single materials. The mechanism of this phenomenon seems to be related to secondary electron emission. © 1999 Scripta Technica, Electr Eng Jpn, 127(2): 1–7, 1999