Dependence of String Electron Current on Array Plasma Aspect Angle and Temperature

Abstract

In most cases, the incident aspect angle of a photovoltaic array to the local plasma continuously changes for a spacecraft in low Earth orbit. It is possible to simulate the combined effects of changing array ram aspect angle with respect to the plasma flow inside a vacuum chamber. On-orbit solar array collected current will significantly vary as a function of the angle between the spacecraft velocity vector and the solar array front surface normal vector. The purpose of this paper is to extract this angular dependence of electron current collection of UltraFlex solar array coupons, as well as to measure the dependence of string electron collection current on array temperature. It is found that collected current can be approximated by a cosine function with a 70% drop when the array coupon front surface normal vector is rotated to an angle from 15° to 90°. It was also determined in subsequent tests with two electron number densities of Ne = 0.5 · 106 cm-3 and 1.0 · 106 cm-3 that electron current collection does not depend on the sample temperature.