<h2>AAS  96-126</h2><h2>DRAG COEFFICIENTS OF SPHERES IN FREE-MOLECULAR FLOW</h2><h4>K. Moe, Space and Missle Systems Center; M. M. Moe and S. D. Wallace, University of California - Irvine</h4><h2> Abstract </h2>Satellite drag measurements in low-earth orbit usually yield information on the product of air density and drag coefficient (Cd).  In astrodynamics, Cd is used in two different senses:  (1) as a fitting parameter that constrains a thermospheric model to agree with the observed orbital decay, and (2) as a physical quantity that defines the in-track component of the force of interaction of air molecules with the satellite.  In the present paper, we calculate physical drag coefficients from the models of Sentman and Schamberg, using  orbital measurements of gas-surface interactions to infer the appropriate parameters in the models.<br><br>