George P. Newton

Atmospheric density and temperature variations from the explorer XVII satellite and a further comparison with satellite drag

Abstract Hundreds of direct, in situ atmospheric density measurements were made at satellite altitudes during the three month interval from April to June 1963. At northern mid-latitudes the density varied by at least a factor of four at 270 km and a factor of ten at 450 altitude. At 360 km altitude the average density had a diurnal variation of a factor of five with a maximum value between 1200 and 1500 hr. The diurnal temperature varied between a maximum of 1000°K and a minimum near 500°K. A large variation in density scale height was observed for altitudes above 400 km near the time of local sunrise. A greater degree of heating of the atmosphere occurred for small variations in the planetary geomagnetic index than was previously expected. For example, an increase of 70°K would result from a variation of Ap, from two to eight ; this change correlates with a solar wind speed change from 350 to 430 km/sec. The drag-determined densities were found to be a factor of two greater than the averaged gauge densities. It was concluded that a latitude dependence of the density in the interval 35°N to 55°N must be less than a factor of two. An indication was found of a significant amount of hydrogen in the atmosphere above 800 km altitude. Fluctuations of a factor of two in the density were observed which do not correlate with known activity indices such as 10.7 cm solar index or daily geomagnetic planetary index. One such fluctuation correlates with a reported increased intensity of the day airglow 6300 A oxygen line. These fluctuations suggest that caution should be used in interpreting results obtained by combining measured quantities with model atmosphere values.

Pressure Conversion Constants for Magnetron Ionization Gauges

The gas calibrations of the Explorer 32 satellite atmospheric density experiment provided comparisons of the operation of the following five kinds of ionization gauges: (1) flight type, glass enveloped, cold cathode, magnetron gauge (model NRC-528), (2) flight type, metal enveloped, cold cathode, magnetron gauge (model GCA-R5), (3) commercially available, glass enveloped, “Redhead gauge” (model NRC-552), (4) flight type, metal enveloped, warm cathode, magnetron gauge (WCM), and (5) commercially available, metal enveloped, Penning-type gauge (model GE-22GT210).The nitrogen pressure responses of these gauges are compared in terms of the conversion constant (C). C is the ratio of the cathode current to the pressure and is related to the number of ions produced per neutral particle in the gauge. The 552 and R5 gauges exhibit values of C which axe maximum between 10−10 and 10−9 Torr and decrease at higher pressures. In contrast to this behavior the 528 and 22GT210 gauges exhibit primarily increasing C values w...

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

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).