Relevance of Gas-Surface Interactions for Thermospheric Science and Monitoring

Abstract

Accurate estimates of neutral mass densities obtained from measurements of satellite drag acceleration are vital to NASA science objectives, including the construction of atmospheric models, the understanding of thermospheric physics and its influence on other regions of geospace, the investigation of long-term behavior in the thermosphere, and the monitoring of space weather impacts on operational assets. The interpretation of drag measurements depends strongly on the assumptions made about molecular interactions with a satellite's surfaces, which vary with altitude and local time, with changes in the thermosphere resulting from space-weather, as well as with long-term (multi-decadal) variations in the atmosphere. Through the modification of the aerodynamic drag coefficient (CD), such assumptions introduce errors into atmospheric models and limit our ability to assimilate diverse datasets into operational models.Though recent progress has been made in the area of gas-surface interactions (GSI), there is still much that is unknown about this topic, especially above the Oxygen/Helium transition where most low Earth orbiting satellites reside. In order to take full advantage of data derived from measurements of satellite drag, it is necessary to quantify GSI parameters throughout the thermospheric column. A successful approach to addressing questions in GSI and drag coefficient modeling will include a combination of techniques. These multiple approaches will require satellite constellations flying now and in the near future, state-of-the-art laboratory experiments, and comprehensive multi-instrument analyses from single satellites that are made possible by upcoming missions such as GDC.