AAS 97-634
NEUTRAL AND ION DRAG EFFECTS NEAR THE EXOBASE: MSX SATELLITE MEASUREMENTS OF He AND O+
O.M. Uy, R.C. Benson and R.E. Erlandson - The Johns Hopkins University Applied Physics Laboratory; G.M. Keating and J.C. Leary - The George Washington University
Abstract
The winter helium bulge near the exobase was first discovered from measurements in the helium regime by a series of spherical drag satellites, Explorers 9, 19, 24, and 39 (Keating and Prior, 1967). The DOD's Midcourse Space Experiment (MSX) satellite, launched in 1996 during solar minimum, flies in a near polar circular orbit at approximately 900 km in the helium regime of the terrestrial upper atmosphere. Near 900 km, the MSX neutral mass spectrometer indicates that the winter helium bulge has a winter to summer pole amplitude near 10 at solar minimum. These are the highest circular orbit mass spectrometer measurements of the helium bulge. The very low helium densities detected near the summer pole increases the required drag effects of atomic oxygen in order to be in accord with drag measurements of total atmospheric densities. It is found that atomic oxygen drag effects near the summer pole estimated by the MSIS and J71 models are an order of magnitude less than what is require