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Flight Simulation of Orbital and Reentry Vehicles Part II - A Modified Flight Path Axis System for Solving the Six-Degree-of-Freedom Flight Equations

Report Number: ASD TR 61-171 Volume 2
Author(s): L. E. Fogarty; R. H. Howe
Corporate Author: University of Michigan
Laboratory: Behavioral Sciences Laboratory
Date of Publication: 1961-10
Pages: 41
Contract: AF 33(616)-5644
Project: 8(7-114)
Task: 611407
AD Number: AD0269283

Three translational and three rotational equilirium equations for an orbital vehicle subject to aerodynamic and jet reaction forces are derived using a modified flight-path axis system for the translational eqations. Dependent variables of the system are horizontal velocity component, vertical velocity component, and flight-path heading angle. Resulting equations are shown to have advantages for computer mechanization over alternative axis systems for the translational equations. Complete equations for determining vehicle orientation, instantaneous latitude and longitude, angle of attack, angle of sideslip, aerodynamic forces and moments, etc., are presented. Modifications in the translational equations which allow direct solution by an analog computer are also given. Analog computer mechanization of these equations in both real and fast time is described, including a novel technique for division which preserves favorable multiplier scaling. Specific machine results are presented which demonstrate accurate solution of close-satellite trajectories, including re-entry from satellite altitudes to sea level.

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