Relation of Measured Outgassing Pressures to Surface Adsorption in Satellite Borne Pressure Gauges

Abstract

Two different pressure gauges were mounted in the Explorer 32, a spin stabilized, aeronomy satellite, in such a way that they were alternately exposed to a beam of atmospheric gas and to a nearly total vacuum. During exposure to the nearly total vacuum, it was possible to measure the pressure in the gauge enclosure produced by gas desorbed from the gauge surfaces. This outgassing pressure was found to depend in a fixed way upon the ambient atmospheric density and the elapsed time since the satellite was last at perigee. The main features of the variation of outgassing pressure with time near perigee were reproduced using a Langmuir model of surface adsorption, with an adsorption probability near 10−4 and a desorption rate from a surface covered with one monolayer of gas near 1013 particles per sq cm per sec. The results of this study show that the adsorption-desorption phenomena have a component that occurs during times comparable to an orbit period (100 min).