FREE MOLECULE FLOW THEORY AND ITS APPLICATION TO THE DETERMINATION OF AERODYNAMIC FORCES

The purpose of this analysis is twofold. It is designed as an introduction to free molecule flow theory for those with no background in rarefied gas dynamics or kinetic theory, and it presents an exact method for the determination of the forces and moments on bodies in a free molecule flow. Approximate methods are evaluated. Comparison with the exact method of this analysis shows that for molecular speed ratios AT SATELLITE ALTITUDES THE APPROXIMATE THEORIES, WHICH DO NOT COMPLETELY ACCOUNT FOR THE RANDOM MOTION OF THE IMPINGING MOLECULES, ARE SATISFACTORY FOR THE PREDICTION OF C sub N and C sub M. For elongated bodies at small angles of attack, the approximate methods are shown to be inadequate for the prediction of C sub A. Tables of certain functions requisite to the determination of free molecule aerodynamic coefficients are presented.