Drag and Aero‐Torque for Convex Shells of Revolution in Low Earth Orbit

Abstract

A numerical procedure is described in which the aerodynamic drag and torque are calculated for convex shells of revolution for any given angle of attack based on free molecular flow theory. Assumptions are that the center of gravity lies on the axis of revolution and that there are no significant appendages. The contours of the shells are considered to consist of strictly concave ascending and descending portions connecting smoothly to an optional horizontal middle section. Each portion is described by a series of parametric equations. The drag profile, that is, the projection of the entire shell, is approximated by the convex envelope of finitely many ellipses. The area of the drag profile and its center of area moment are then calculated and permit determination of drag force and aerodynamic torque. For a given shell, the functional dependence of drag area and aerodynamic eccentricity on the angle of attack can be expressed to a high degree of accuracy in the least‐squares sense by polynomials of low degree suitable for processing in real time.