Improved satellite drag coefficient calculations from orbital measurements of energy accommodation

Significant discoveries about gas-surface interactions that have been made in 90 years of laboratory experiments and 30 years of orbital measurements are reviewed. This information is used to improve the calculation of drag coefficients for satellites in low Earth orbit for several different satellite shapes and orientations by inserting the appropriate parameters in theoretical models of the drag coefficient. The drag coefficients so calculated provide increased consistency in orbital measurements of astmospheric density by satellites of different shapes near 200 km, where adsorbed atomic oxygen dominates the interaction and causes the energy accommodation coefficient to approach unity. It is essential to improve the numerical value of the drag coefficient so that the density of the neutral thermosphere can Ire inferred from satellite drag to better than the present 15% uncertainty. The key to this improvement is the calculation of drag coefficients from parameters measured in space, rather than from those measured in the laboratory under conditions very different from the space environment.