Dependence of orion UltraFlex™ 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 as the array progress through its path about the low Earth orbital plane. 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 vary greatly as a function of the angle between spacecraft velocity vector and the solar array front surface normal vector to the plasma. The purpose of the present work is to extract array/plasma angular dependence of electron current collection of UltraFlex™ solar array coupons, as well as to verify that string electron collection current increases with increasing array temperature. It was found that the array aspect angle to the plasma flow closely approximates a cosine function with a 50% drop in array string electron collected current when the array coupon front surface normal vector is rotated to an angle of ∼54 degrees. It was also confirmed in subsequent independent high density (N e = 1.0×106 cm−3) low earth orbit plasma tests that electron current collection at room temperature (20°C) increased by a nominal ∼2.5% compared with one at cold (−83.4°C) temperature.